Volume 19 (No. 1) - Nigerian Institution of Agricultural Engineers

Transcription

Journal of Agricultural Engineering and Technology (JAET), Volume 19 (No. 1) June, 2011
JOURNAL OF AGRICULTURAL ENGINEERING AND TECHNOLOGY (JAET)
EDITORIAL BOARD
Editor-In-Chief
Professor A. P. Onwualu, FAS
Raw Materials Research and Development Council (RMRDC)
17 Aguiyi Ironsi Street, Maitama District, PMB 232 Garki, Abuja, Nigeria.
aponwualu@niae.net; ponwualu@yahoo.com Phone: 08037432497
Prof. B. Umar – Editor, Power and Machinery
Adamawa State Polytechnic, Yola, Adamawa State, Nigeria.
E-mail: bobboiumar@yahoo.co.uk
Phone: 08023825894
Prof. A. A. Olufayo – Editor, Soil and Water Engineering
Agricultural Engineering Department, Federal University of Technology, Akure, Nigeria.
E-mail: ayo_olufayo@yahoo.com
Phone: 08034708846
Prof. A. Ajisegiri – Editor, Food Engineering
College of Engineering, University of Agriculture, Abeokuta, Ogun State, Nigeria.
E-mail: ajisegiri@yahoo.com
Phone: 08072766472
Prof. K. Oje – Editor, Processing and Post Harvest Engineering
Agric. and Bio-resources Engineering Department, University of Ilorin, Nigeria.
E-mail: kayodeoje2@yahoo.com
Phone: 08033853895
Dr. A. El-Okene - Editor, Structures and Environmental Control Engineering
Agricultural Engineering Department, Ahmadu Bello University, Zaria, Nigeria.
E-mail: abdullahielokene@yahoo.com Phone: 08023633464
Prof. D. S. Zibokere – Editor, Environmental Engineering
Agric. and Environmental Engineering Dept., Niger Delta University, Wilberforce Island, Yenegoa.
E-mail: zibokere@yahoo.co.uk
Phone: 08037079321
Prof. C. C. Mbajiorgu – Editor, Emerging Technologies
Agricultural and Bioresources Engineering Department, University of Nigeria, Nsukka, Nigeria.
E-mail: const.c.mbajiorgu@talk21.com Phone: 07038680071
Prof. (Mrs) Z. D. Osunde – Editor, Processing and Post Harvest Engineering
Agricultural Engineering Department, Federal University of Technology, Minna, Nigeria.
E-mail: zinashdo@yahoo.com
Phone: 08034537068
Mr. Y. Kasali – Business Manager
National Centre for Agricultural Mechanization, PMB 1525, Ilorin, Nigeria.
E-mail: ncam@skannet.com
Phone: 08033964055
Mr. J. C. Adama – Editorial Assistant
Agricultural Engineering Department, University of Agriculture, Umudike, Nigeria.
E-mail: josephadama@yahoo.com
Phone: 08052806052
Dr. B. O. Ugwuishiwu – Editorial Assistant
Agricultural and Bioresource Engineering Department, University of Nigeria, Nsukka, Nigeria.
E-mail: ugwuishiwubo@yahoo.com
Phone: 08043119327
Miss I. C. Olife – Technical Assistant to Editor-In-Chief
Raw Materials Research and Development Council, Abuja
E-mail: ifeeolife@yahoo.com
Phone: 08033916555
Nigerian Institution of Agricultural Engineers © www.niae.net
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Aims and Scope
The main aim of the Journal of Agricultural Engineering and Technology (JAET) is to provide a medium
for dissemination of high quality Technical and Scientific information emanating from research on
Engineering for Agriculture. This, it is hoped will encourage researchers in the area to continue to
develop cutting edge technologies for solving the numerous engineering problems facing agriculture in
the third world in particular and the world in general.
The Journal publishes original research papers, review articles, technical notes and book reviews in
Agricultural Engineering and related subjects. Key areas covered by the journal are: Agricultural Power
and Machinery; Agricultural Process Engineering; Food Engineering; Post-Harvest Engineering; Soil and
Water Engineering; Environmental Engineering; Agricultural Structures and Environmental Control;
Waste Management; Aquacultural Engineering; Animal Production Engineering and the Emerging
Technology Areas of Information and Communications Technology (ICT) Applications, Computer Based
Simulation, Instrumentation and Process Control, CAD/CAM Systems, Biotechnology, Biological
Engineering, Biosystems Engineering, Bioresources Engineering, Nanotechnology and Renewable
Energy. The journal also considers relevant manuscripts from related disciplines such as other fields of
Engineering, Food Science and Technology, Physical Sciences, Agriculture and Environmental Sciences.
The journal is published by the Nigerian Institution of Agricultural Engineers (NIAE), A Division of
Nigerian Society of Engineers (NSE). The Editorial Board and NIAE wish to make it clear that statements
or views expressed in papers published in this journal are those of the authors and no responsibility is
assumed for the accuracy of such statements or views. In the interest of factual recording, occasional
reference to manufacturers, trade names and proprietary products may be inevitable. No endorsement of
a named product is intended nor is any criticism implied of similar products that are not mentioned.
Submission of an article for publication implies that it has not been previously published and is not being
considered for publication elsewhere. The Journal’s peer review policy demands that at least two
reviewers give positive recommendations before the paper is accepted for publication. Prospective
authors are advised to consult the Guide for Authors which is available in each volume of the Journal.
Four copies of the manuscript should be sent to:
The Editor-In-Chief
Journal of Agricultural Engineering and Technology (JAET)
℅ The Editorial Office
National Centre for Agricultural Mechanization (NCAM)
P.M.B. 1525
Ilorin, Kwara State,
Nigeria.
Papers can also be submitted directly to the Editor-In-Chief or any of the Sectional Editors. Those who
have access to the internet can submit electronically as an attached file in MS Word to
aponwualu@niae.nt; ponwualu@yahoo.com. All correspondence with respect to status of manuscript
should be sent to the Technical Assistant to the Editor In Chief at ifeeolife@yahoo.com.
ii
TABLE OF CONTENTS
Editorial Board
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Aims and Scope
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Table of Contents
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Development of Outdoor Soil Bin Facility for Soil Tillage Dynamics Research
S. I. Manuwa, O. C. Ademosun, L. A. S. Agbetoye and A. Adesina
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The Effect of Different Tillage Treatments on the Performance of Okra
(Abelmoschusesculentus)
S. O. Nkakini and I. Fubara-Manuel
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Design of a Low-cost Cocoa Oil Expeller
O. S. Ogundipe, S. I. Obiakor, F. B. Olotu, O. A. Oyelade and J. A. Aransiola
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Development and Performance Evaluation of a Dough Kneading Machine with
Adjustable Nip
U. N. Onwuka, O.A.U. Okafor-Yadi, and N. P. Njiuwaogu
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Development of Metal-in-Wall Evaporative Cooling System for Storing Perishable
Agricultural Produce in a Tropical Environment
F. R. Falayi and A. O. Jongbo
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Modeling Incubation Temperature: the Effects of Incubator Design, Embryonic
Development and Egg Size
M. M. Jibrin, F. I. Idike, K. Ahmad and U. Ibrahim
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Modification and Performance Evaluation of African Bush Mango
(Irvingia Gabomensis) Cracker
E. A. Ajav and R. A. Busari
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Development of a Digital Densitometer
S. L. Ezeoha, C. C. Mbajiorgu and V. U. Obi
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Development and Testing of a Bambara Groundnut Pod Shelling Machine
N. I. Nwagugu and C. O. Akubuo
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Status of Aquacultural Mechanization in South Eastern Nigeria
C. C. Anyadike, S. C. Duru and O. A. Nwoke …
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Modeling Hot Air Drying Characteristics of Red Bell Pepper (Capsicum Annum. L)
A. L. Musa-Makama and Mohammed Abdullahi
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Biogas Production in Nigeria – Potentials and Problems
L. C. Orakwe, E. C. Chukwuma and C. B. Emeka-Orakwe
Guide for Authors
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DEVELOPMENT OF OUTDOOR SOIL BIN FACILITY FOR SOIL
TILLAGE DYNAMICS RESEARCH
S. I. Manuwa, O. C. Ademosun, L. A. S. Agbetoye and A. Adesina
Department of Agricultural Engineering, The Federal University of Technology,
PMB 704 Akure, Nigeria
E-mail: sethimanuwa@yahoo.com
ABSTRACT
Outdoor soil bin is sine qua non for soil/tool interaction studies especially for the testing and evaluation
of commercial, full scale tools and implements. However, such facilities are not common in Nigeria. This
paper describes aspects of the development of outdoor soil bin test facility at The Federal University of
Technology, Akure (FUTA), Nigeria. The facility consists of the following: a stationary 48 m long by 1.5
m wide and 1.2 m deep soil bin; an implement carriage system and implement carriage sub system with a
tool bar; two compaction rollers- one smooth and the other spiked; a leveling blade; instrumentation
devices and controls. The instrumentation system was developed with load cells and load cell amplifiers
for the measurement of soil/tool interaction forces and moments. The load cell was connected to load cell
amplifier and also data logger and laptop in order to boost resulting voltages, data acquisition, storage and
processing. Preliminary tests were conducted with the test facility with a standard mouldboard plough.
The outdoor soil bin test facility is adequate for the testing and evaluation of commercially produced soil
engaging tools and implements.
KEYWORDS: Outdoor soil bin, instrumentation system, tillage tools, implements, soil dynamics.
1. INTRODUCTION
Soil mechanics and its applications have been identified as very important aspects for tillage and the
design and development of soil engaging implements. It has been enhanced by the theories developed by
Coulomb in 1779, Rankine in 1857 and Mohr in 1873 (Soehne, 1985). Most of the early studies on
different soils were done in the field using full scale or commercial implements. It has also been reported
(Al-Janobi and Eldin, 1997) that due to the wide variation of soil types and conditions in the field, the
results obtained were sometimes meaningless. Also the chance of getting the same soil at the same
condition for repeating the experiment was very rare. Such problems are largely overcome use of soil bin
facility in soil-tillage –tool interaction studies. Controlled studies are possible in soil bins where the
operating parameters can be controlled and the experiments closely observed and monitored. In that case
many field difficulties could be avoided. Soil bin facilities vary in scope from small indoor bins to large
outdoor soil bins, depending on the main objectives of development, space available, and financial
constrains (Wismer, 1984).
The soil bin described was designed to meet the following requirements.
(i) To provide consistent homogenous and isotropic soil conditions for studies concerned with the
testing of model and full scale soil engaging implements and the validation of force predicting
models.
(ii) To utilize where possible commercially available equipment and instrumentation for the purpose
of studies in soil-tool interaction.
(iii) To minimize capital costs and moderate the manual labour requirements
Existing designs of soil bin range from the large scale bins of the National Tillage Machinery Laboratory
(USDA, 1974) where full scale implement testing is carried out to small automated soil bins similar to
that described by Siemens and Weber (1964). Other researchers have also reported on soil bins and
facility developed by them (Mamman and Oni, 2005; Ademosun et al., 2006; Manuwa, 2002; Wood and
Wells, 1983; Onwualu et al., 1998). At the Department of Agricultural Engineering, The Federal
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University of Technology, Akure (FUTA), Nigeria, when the existing indoor soil bin could not permit the
testing of full size equipment, the need arose to develop an outdoor soil bin.
The main objective of this paper therefore is to describe aspects of the development of outdoor soil bin
test facility at FUTA, Nigeria.
2. MATERIALS AND METHODS
2.1 Development of Outdoor Soil Bin Facility
The soil bin facility consists of the following major components: the soil bin; the soil fitting equipmentcompaction roller, leveling blade; tool carriage and tool carriage sub frame, load cells. Figure 1 gives the
general overview of the soil bin facility.
(a)
(b)
(c)
(d)
(e)
(f)
Figure 1. General overview of the soil bin facility - (a) Smooth compaction roller (b) Spiked compaction
roller (c) Implement carriage system (d) Implement carriage subsystem (e) Instrumentation system (f)
Soil bin (unloaded with soil)
2.2 Design Considerations
In planning the new soil bin facility, the following design considerations were taken into account: 1) the
goals of the research programme- long range or short term; 2) the technical nature and the degree of
difficulty of carrying out the programme-research, development, or testing; 3) the type and volume of the
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programme to be carried out; 4) the personnel and funds available to be dedicated to support the
programme in general, to maintain and adapt test devices to dynamometers, and to redesign or remodel
the facility; 5) potential cooperators, their possible contributions and their possible demands; 6) the
personnel, funds and equipment available to be dedicated to the planning of the work, analysis, and
evaluation of project data, preparation of project report and overall management of the programme; 7) the
space available for the soil bin and its support facilities; 8) the size and weight of the machine or machine
components that are to be used in the programme; and 9) the operating speeds, power, and force
requirements needed to fulfill the research programme requirements.
2.3 Soil Bin and Soil Fitting Equipment
Soil fitting is defined as the process used to prepare the bin soils to provide desired soil conditions. The
soil fitting sequence usually begins with the leveling of the soil surface with a blade to refill irregularities,
pits and furrows, and to make sure there is an even distribution of soil side-to-side and end-to-end of the
bin.
2.3.1 Soil Bin
The soil bin facility is equipped with a soil bin with dimensions 48.0 x 1.5 x 1.2 m (length, width and
height, respectively). The walls of the soil bin were constructed with concrete blocks. The blocks were
clad with bin wall panels for better reinforcement, rigidity, and efficient and effective behavior of bin
walls in service. The bin wall panel was fabricated from mild steel plate 8 mm thick, inverted L-section
150 x 1050 x 2400 mm, with drilled holes for installation.
The steel rails (two in number) run parallel to each other along the whole length of the bin. They are made
from steel angle sections 150 x 150 x 10 mm and installed on concrete shoulder of the bin by means of
drilled holes (on the railings) 12 mm diameter countersunk at 60 degrees at 1.0 m intervals. The
implement carriage was designed to run on the railings which horizontal surface width was compatible
with the running wheels of the implement carriage.
2.3.2 Soil Leveling Blade
The leveling blade consisted essentially of a plane steel board with light curvature, 1400 mm wide and
350 mm height, It was reinforced at the to provide sufficient strength and rigidity. Provision was made by
means of slot-pinning device to attach it to the tool bar (Fig. 2). The preparation of the soil was normally
done by compaction of the soil in layers while the roller was towed by the tractor. Water was normally
sprayed on the soil using a sprinkler device to vary (increase) the moisture content. The state of
compactness of the soil was monitored by the use of a Bush recording penetrometer (CP 20 Ultrasonic).
Figure 2. Leveling blade
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2.3.3 Smooth Compaction Roller
The soil compaction roller consisted mainly of a cylindrical drum, the roller axle and bearing and ballast
weights (Fig. 3). The diameter and length of the roller drum were 700 and 1350 mm, respectively. The
coupling frame width and length were 1700 and 400 mm, respectively. The weight of the roller without
the ballast weights was 85 kg. Ten weights each of 5 kg were provided for ballasting. The axle of the
compaction roller was supported in two bearing housing. Provision was made for the roller to be moved
in the vertical direction or be suspended in space through the position adjustment device. The vertical
adjustment was accomplished by raising or lowering the roller through the vertical adjustment. The roller
was designed to be coupled to the implement carriage and its major function is to compact the bin soil in
layers as desired for testing.
Figure 3. Smooth compaction roller
2.3.4 Spiked roller
The spiked roller is similar to the smooth roller and has the same dimension. However, it has spikes
welded to the surface along the periphery (Figure 4). The spikes are of length 20 mm and diameter 20
mm. The function of the spiked roller was to ensure a satisfactory bond between successive soil layers,
the surface of each freshly compacted layer is scored to a depth of 10 mm before placing the next layer.
Figure 4. Spiked tooth compaction roller
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2.4 Implement Carriage System
The implement carriage was fabricated using rectangular hollow section steel (RHS) of dimension 100 x
100 mm and is supported on four wheels mounted on the main frame by four wheel mounting brackets
(Figure 5). The arrangement of the wheels was designed to run on the side railings of the soil bin. The
carriage has a 3-point linkage and also an implement coupling recess to enhance the rigid coupling of the
tool carriage sub system. The carriage dimension is 1.623 m x 0.70 m x 1.117 m of length, width and
height, respectively. The main function of the carriage is twofold: firstly to mount the carriage subsystem
which in turn carries the toolbar in place; secondly, for mounting any tillage or traction devices such as
traction or towed wheels for testing or for transportation. The carriage can be coupled to the power source
through the 3-point linkage.
Figure 5. Implement carriage system
The implement carriage subsystem consisted basically of a rectangular main frame designed to stand on
four detachable steel legs (Figure 6). In the middle of the frame was welded a rake meter for varying the
angle of approach of mounted tool or implement. Also, at that point below the rake meter is a mounting
device to hold the tool bar rigidly in place. The carriage subsystem has dimension of 1.395 mm x 600 mm
x 667 mm of length, width and height, respectively. Two mounting studs were also welded in place to
secure rigidity with the implement carriage.
Figure 6. Implement carriage subsystem
The tool bar was fabricated from 57 mm square section solid bar of length 1.372 m equipped with tool bar
clamp devices for tool/ implement coupling.
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2.5 Prime Mover
The power unit is an MF 415 tractor with the following specifications: power, 31.6 kW; 2WD; Diesel
engine; water cool; oil bath air cleaner with PTO drive shaft and 3-point linkage; a good range of forward
speeds (2.59 – 34.21 km/h); a slow and fast reverse speeds of 3.5 and 14.2 km/h, respectively.
2.6 Instrumentation and Data Acquisition System
The instrumentation system consists of load cells, strain gauge amplifiers, data acquisition system
including data logger. The data acquisition system of the test facility is located somewhere on the power
unit (Figure 7). This dedicated system is made up of some sensor (load cell) outputs interfaced to a
computer (lap top) system and a data logger. The computer system can receive, monitor, display and store
the measured signals from the respective load cells. Details can be found in Manuwa (2002).
Figure 7. Data acquisition system located on the power unit
2.7
Preliminary Tests
Draught is an important parameter for measuring and evaluating implement performance for energy
requirements (Grisso et al., 1996). The availability of draught requirement data of tillage implements is an
important factor in selecting suitable tillage implements for a particular farming situation (Al-Janobi and
Al-Suhaibani, 1998). Farm managers and consultants use draught and power requirement data of tillage
implements in specific soil types to determine correctly the proper size of tractor required. Preliminary
tests were carried out to evaluate the effects of forward speed and depth of operation on the draught
requirement of a standard one-bottom mould board plough in the outdoor soil bin filled with a clay loam
soil.
The soil was a clay loam (35% sand, 26% silt and 39% clay). Atterberg limits were 44.1% for liquid limit
and 22.4% for plastic limit. The soil fitting equipments were used to prepare the soil to desired
conditions. After each experimental run, the soil was leveled and re-compacted with rollers to desired
condition of bulk density and cone index. Soil penetration resistance (cone index) was measured with a
Rimik Penetrometer (model CP 20 ultrasonic, Agridy Rimik Pty Ltd, Toowoomba, Australia). The
penetrometer had in-built data logger, 500 mm long shank, cone with a base area of 129 mm2 and an apex
angle of 300. The penetrometer was pushed into the soil by hand at a speed of approximately 0-2 mm/s
according to ASAE standards. Implement working depth was measured by a steel rule and tractor forward
speed was determined from the measurement of the distance travelled along the soil bin during the
operation and the time taken. During the tests, moisture content ranged from 7.5 to 11.6 (%db), bulk
density (1.26 to 1.65 Mg/m3), cone penetration resistance (350 to 800 kPa).
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The tillage implement used was a standard mouldboard plough (one body 360 mm wide). The parameters
investigated for the draught measurements were forward speed and tillage depth. Four speeds and two
depths were used in combination for 8 treatments. The selected speeds used for the tillage experiment
were 0.8, 1.4, 2.0 and 2.5 m/s. The operating depths were 10 and 15 cm. Depth was measured as the
vertical distance from the top of the undisturbed soil surface to the implements deepest penetration. The
instrumentation described above (section 2.6) measured and recorded implement draft.
3. RESULTS AND DISCUSSION
The mean values of draught of the mouldboard plough at different speeds and depths are presented in
Table 1. The results showed an increasing response in draught in all the treatments with an increase in
forward speed and depth of operation. Similarly, draught also increased with increase in forward speed.
These observations agree well with reports of other researchers (Grisso et al., 1996; Al-Janobi and AlSuhaibani, 1998; Manuwa, 2009).
Table 1. Mean draft and standard deviation of mouldboard plough at various speeds and depths of
operation
Speed
Mean Draught Stdev
Mean Draught Stdev
m/s
kN
kN
kN
kN
Depth 1(100 mm)
Depth 2 (150 mm)
0.8
5.72
0.132
8.43
0.215
1.4
6.26
0.116
9.37
0.179
2.0
7.24
0.272
12.06
0.114
2.5
9.37
0.190
13.95
0.207
Draught, N
Stdev = standard deviation
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14
12
10
8
6
4
2
0
d1(100mm)
y = 1.0672x2 - 0.1486x + 7.7732
R² = 0.9893
y = 1.4002x2 - 2.5465x + 6.9147
R² = 0.9912
0
1
2
3
Speed, m/s
Figure 7. Effect of speed and depth on draught acting on a standard mouldboard plough
Figure 7 shows the variation of draught of the mould board plough with forward speed at different depths
of operation. At greater depth of operation, the draught was higher, as it is expected. The best fit
regression equation was a polynomial equation of the second order degree with high coefficient of
determination. More tests were required to generate more data for more extensive multiple regression
analysis for predictive purposes.
The following tests can be performed using the soil bin facility and associated equipment described in this
paper: (i) Performance evaluation of tillage tools including indigenous tools on Nigerian soils (ii) Studies
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in land application of biosolids to effectively and efficiently utilize organic manure for sustainable crop
production (iii) performance evaluation of traction and tractive devices that are utilizable with tillage
implements and vehicle mobility on Nigerian soils.
4. CONCLUSIONS
An outdoor soil bin facility has been developed for fundamental research on soil/tool interaction with full
scale tillage implements or traction devices. The facility consists of a large size soil bin, power unit,
implement carriage and carriage sub system, soil fitting equipment and an instrumentation system for
measuring forces. Results of preliminary tests showed that the outdoor soil bin facility can be used to
obtain reliable results from soil bin experimentation of tillage tools.
ACKNOWLEDGEMENT
The authors are grateful to the World Bank for the Research Grant which provided financial support for
this study through the FUTA STEP-B Project.
REFERENCES
Ademosun, O. C., Manuwa, S. I. and Ogunlowo, A. S. 2006. Development of an in-door Soil Bin Facility
for Soil Tillage Dynamics Research. FUTA Journal of Engineering and Engineering Technology
Research. Vol. 5 (1): 31-36.
Al-Janobi, A. and A. M. Eldin, 1997. Development of a soil bin test facility for soil tillage tool interaction
studies. Res. Bult., No. 72, Agric Res Center, King Saud University, pp (5- 26).
Al-Janobi, A. A. and S. A. Al-Suhaibani. 1998. Draft of Primary Tillage Implements in Sandy Loam
Soil. Applied Engineering in Agriculture, Vol. 14(4):343-348.
Grisso, R. D.; Yasin, M. and Kocher, M. F. 1996.Tillage Implement Forces Operating in Silty Clay
Loam. Transactions of the American Society of Agricultural Engineers. Vol. 39 (6): 1977 – 1982.
Siemens J. C. and Weber J. A. 1964. Soil bin and model studies on tillage tests and traction devices.
Journal of Terramechanics, 1 (2): 56- 67.
Mamman, E. and K. C. Oni. 2005. Draught performance of a range of model chisel furrowers.
Agricultural Engineering International: the CIGR Ejournal. PM 05 003.Vol. VII. November 2005.
Manuwa, S. I. 2002. Development of an equipment for soil tillage dynamics and evaluation of tillage
parameters. Unpublished PhD Thesis in the Department of Agricultural Engineering, The Federal
University of Technology, Akure, Nigeria.
Manuwa, S. I. 2009. Performance evaluation of tillage tines operating under different depths in a sandy
clay loam soil. Soil and tillage research, 103: 399- 405.
Onwualu A. P. and K. C. Watts, 1989. Development of a soil bin test facility. ASAE Paper No. 89- 1106,
ASAE, St Joseph: Michigan.
Onwualu, A. P. and Watts, R.C. 1998. Draught and vertical forces obtained from dynamic soil cutting by
plane tillage tools. Soil Tillage Research, 48: 239-253.
USDA 1974. The National Tillage Machinery Laboratory, U.S. Department of Agriculture, Agricultural
Research Service.
Wismer R. D. 1984. Soil bin facilities: characteristics and utilization. In Proc. 8th International conference,
International society for terrain- vehicle systems, Vol. III: 1201- 1216. 6 10 August, Cambridge,
England.
Wood, R. K. and Wells, 1983. A soil bin to study compaction. ASAE Paper No. 83- 1044. ASAE, St
Joseph: Michigan.
8
THE EFFECT OF DIFFERENT TILLAGE TREATMENTS ON THE
PERFORMANCE OF OKRA (Abelmoschusesculentus)
S. O. Nkakini and I. Fubara-Manuel
Department of Agricultural and Environmental Engineering,
Rivers State University of Science and Technology, Port Harcourt, Nigeria
nkakini@yahoo.com
ABSTRACT
The performance of okra (Abelmosehus esculentus) on soil bulk desity and different tillage treatments in a
sandy loam soil was investigated. Tillage treatments applied were zero tillage (To), ploughing only (T 1),
ploughing and harrowing (T2), ploughing and double harrowing (T3) and ridging (T4). The treatments
were assigned into a randomized complete block design with three replications. Two tillage depths of 0150mm and 150-300mm were considered. Bulk densities were also measured at each tillage treatment and
depth. Crop parameters considered were number of plants per plot, number of fruits per plant, plant
height, number of leaves per plant, fruit length and diameter, and yield. Statistical analysis revealed that at
the 5% level of significance, there was no significant difference (p≥0.05) in bulk density, including
growth parameters such as plant height and number of leaves in treatments, while there was significant
difference (p≤0.05) in depth. Results indicated that except for plant height and number of leaves,
ploughing and double harrowing (T3), gave the maximum values of plant parameters at an average bulk
density of 1.79g/cm3.The highest values of plant height and number of leaves were obtained from
ploughing and harrowing (T2) at an average bulk density of 1.90g/cm3, and ridging (T4) at an average bulk
density of 1.78g/cm3 respectively. However, the lowest yield was obtained from ridging (T4), while the
lowest except plant height, were obtained from zero tillage (To) at an average bulk density of 1.96g/cm3.
Result from this study therefore suggested that the best growth performance of okra in a sandy loam soil
can be obtained from a combination of ploughing and double harrowing. This conventional tillage is
recommended for Okra production, for this soil and location.
KEYWORDS: Tillage operation, bulk density, okra performance, tillage, plough.
1. INTRODUCTION
Okra is a vegetable crop that belongs to the genus Abelmoschus, family of Malvaceae and has two main
species: Abelmosechus esculentus and Abelmoschus Caillei (Siemonsma, 1982). Okra, (Abelmosehus
esculentus) is one of the most popular vegetable crops. The fruits are mucilaginous and are commonly
used as a soup thickener in Nigeria. It is used in the making of fish lines, salad dressings, ice-creams,
cheese and candies. Okra contains carbohydrates, proteins and vitamin c in large quantities (Adeboye and
Oputa, 1996). It plays a vital role in human diet. The dried seeds are nutritious material and may be used
to prepare vegetable curds or roasted and ground coffee additives or substitute (Markose and Peter, 1990).
Soil tillage is among the important factors that affect crop yield. According to Khurshid et al., (2006),
tillage operations contribute up to 20% of Okra production factors. Tillage is mechanical manipulation of
soil to develop a desirable soil structure for a seedbed and good surface configuration for crop planting
(Aluko and Lasisi, 2009; Nkakini et al., 2008). Proper tillage practices can be used to improve soil related
constraints, while improper tillage may cause a range of undesirable processes, such as destruction of soil
structure, accelerated erosion, depletion of organic matter, disruption of water cycle, organic carbon and
plant nutrient (Lal, 1993). Hakimi and Kachru, (1976) reported that the physical properties of soil are
influenced by tillage operations. Conservation tillage methods often results in decrease in soil pores and
increase in soil strength (Hill, 1990, Bauder et al., 1981). This tillage method modifies soil structure by
changing its physical property such as soil bulk density (Khan et al., 1999). According to Nkakini et al.,
(2008), no- tillage operation produced the highest value of bulk density of 1.43g/cm3, closely followed by
9
1.24g/cm3 in ploughed operation and 1,18g/cm3 in ploughed plus harrowed operations at the depths of 050mm, 50-100mm and 100-150mm respectively in sandy loam soil.
This study showed that soil bulk density increased with tillage depths under all tillage treatments. Rashid
and keshavarzpour (2007) in their reports indicated that the annual soil disturbance and pulverizing
caused by conventional tillage method produced a finer and loose soil structure which in turn affects the
seedling emergence, plant population density and consequently crop yield. The statistical results of the
study indicated that tillage methods significantly affected crop yield, fruit weight, fruit length, fruit
diameter and total soluble solid.
Thus, there has come to be the need to develop tillage operation standards for different soil types and
conditions to solve specific problems of soil treatment and crop production. This is so since the
understanding of all the factors and soil interactions are not yet fully known.
The objective of this research is to ascertain how various tillage operations will affect the growth and
yield of Okra in the location under study.
2.1 Experimental Site
The research was initiated in 2008 and the field experiments were for a period of one growing season at
the Research Farm of the Rivers State University of Science and Technology, Port Harcourt, Nigeria.
Port-Harcourt is on latitude 0.50 0.1.N, longitude 0.60 57E with an altitude of 274mm. The study area is
characterized by tropical rainforest vegetation, with a rainfall depth ranging from 2000-2484mm per
annum, of which 70% occur between the months of May and August. The rest of the year is relatively
dry. Mean temperature varies from 24 to 30oc.The soil type is ultisol (USDA classification) and its texture
is sandy loam (Ayotamuno et al., 2007).These are quite suited for Okra production.
2.2 Experimental Field Design and Treatment Applications
The experiment was laid out in a randomized complete block design (RCBD) having three replications.
The area of the field was 16m by 22m. The field was cleared and stumped manually. The field was
divided into twelve (12) plots of 4m by 4m each, besides an alley of 10m separating the plots on opposite
sides. Treatment plots were thus 2m apart from each other. Disc plough and harrow implements were
used for initial soil preparation of the plots at a ploughing depth of 150mm. The tillage treatments used
were designated as To (Zero tillage), T1 (ploughing only), T2 (ploughing and harrowing), T3 (ploughing
and double harrowing), and T4 (ridging).
2.3 Soil Bulk Density Measurement
Core samplers were used to collect samples from the site for two different depths 0-150mm and 150300mm. For this test six undisturbed samples were taken from the plot with the core samplers and dried
24hrs at 105oc in an oven (ASAE Standards 1965). The soil samples were collected the same day for
accuracy in their results. This was done for bulk density. The soil bulk density on dry basis was
determined for each treatment.
2.4 Evaluation of Plant Parameters
Seed emergence rates were monitored and evaluated 5 days after planting starting from 1st to 5th of June
2008. Two (2) weeks after complete emergence, that is on 21st of June 2008, the height of the plants were
taken. After another 2 weeks, that is on 5th of July, 2008, plant heights were also taken. Alongside with
the plant heights, number of leaves per plant were also noted as stated above. The number of flowers per
10
plot was monitored. Plant flowering started on 25th of July, 2008 until the final flowering was recorded on
30th of August 2008. At harvest, number of fruits per plant, weight of fruit (kg), fruit length (mm) and
fruit diameter (mm) were measured.
2.6 Data Analysis
The statistical models used to analyze the data were ANOVA and regression analysis. Analysis of
variance was carried out on the data to test for the significance of the treatment effects. The treatment
means were compared using 95% confidence intervals at a probability of type one error of 0.05.
Sieve analysis showed that the soil was a sandy loam with composition of 71% sand, 8.47% silt and
17.94% clay using the textural triangle reading.
Table 1. Mean values for Okra performance and yield
Treatments Mean bulk Number
Number
Plant
density
of plants of fruits
height
(0-300mm) per plot
per plant (mm)
g/cm3
To
1.96
18.49
3.01
72.8
T1
1.92
22.52
3.40
82.7
T2
1.90
27.24
4.35
86.0
T3
1.79
30.26
5.27
66.7
T4
1.78
19.12
3.04
52.3
Plant
leaf
count
Fruit
length
(mm)
Fruit
diameter
(mm)
Yields
kg/ha
4.48
5.22
5.33
5.33
5.77
41.8
52.8
61.7
68.2
53.7
11.0
29.2
30.0
31.5
22.8
3.92
4.53
7.50
17.69
3.47
Table 1 shows that for zero tillage (To) with an average bulk density of 1.96g/cm3, the average number of
plants per plot was 18.49, the number of fruits per plant was 3.01 while the yield was 3.92kg/ha. For
ploughing alone (T1) with an average bulk density of 1.92g/cm3, the corresponding values were 22.52,
3.40 and 4.53 kg/ha. On the whole, ploughing and double harrowing (T3) with an average bulk density of
1.79g/cm3 gave the highest values of 30.26, 5.27, and 17.69 kg/ha for number of plants per plot, number
of fruits per plant, and yield respectively. The least values except for yield and plant height were obtained
from zero tillage (To). Ridging alone (T4) gave the minimum plant height and yield.
Figure 1 shows the effect of tillage treatments on bulk density. There was an increased bulk density in
Zero tillage than others. The highest mean bulk density of 1.93g/cm3 at depth of 0-150mm and 1.98g/cm3
at the depth of 150-300mm were recorded in Zero tillage. This was closely followed by ploughing
operation with mean bulk density of 1.89g/cm3 at 0-150mm depth and 1.94g/cm3 at 150-300mm depth.
Ploughing and harrowing plot with mean bulk density of 1.88g/cm3 at 0-150mm depth and 1.91g/cm3 at
150-300mm depth. Ploughing and double harrowing plot recorded bulk density of 1.74g/cm3 at depth of
0-150mm and 1.84g/cm3 at depth of 150-300mm. The ridged plots had the lowest bulk density of
1.68g/cm3 at 0-150mm depths and 1.88g/cm3 at 150-300mm depth. It is clear that the bulk densities
increased with tillage depths in all tillage treatments. These findings which refer to the bulk densities at a
given depth agree with those of kayombo et al., (2002) who reported that soil bulk density increased with
depth under each tillage treatment as the growing season progressed. The findings also agree with the
results of Nkakini et al., (2008), Aluko and Lasisi (2009), Lampulanes and Cantero-Martines (2003).
Rashidi and Keshavarzpour (2007) similarly reported that different tillage treatments affected soil bulk
density. They found that the highest soil bulk density of 1.52g/cm3 was obtained for the No-tillage
treatment and lowest of 1.41g/cm3 for conventional tillage treatment.
11
Bulk densityg/cm3
2
1.95
1.9
1.85
1.8
1.75
1.7
1.65
1.6
1.55
1.5
1.98
1.93
1.94
1.91
1.89
1.88
1.84
1.74
1.88
0-150mm Tillage
Depth
1.68
150-200mm
Tillage Depth
Types of Tillages
Figure 1. Effect of tillage on Bulk density
Table 2: Summary of Analysis of variance (ANOVA)
Parameters
Sources of
Degree of Sum of
variance/s.v
freedom df square SS
Mean square
Calf
Soil Bulk density
Table f
Total variance 8
7
-0.02
-00032
0.100
Treatment
Depth
5
2
4
1
-0.05
-0.06
-0.017
-0.06
0.567
2.00
6.94NS
6.94NS
Block
Error total
3
2
3
0.03
-0.09
0.03
-0.03
0.05
1.000
6.94NS
144.3
13.12
4.13
7.24
100.31
0.03
3.18
1.10
0.18
9.58
0.03
0.28
2.28
31.54
0.05
1.00
3.93
0.64
34.21
0.05
1.00
Plant Height
Total variance 12
11
Plant Leaf count
Treatment
5
Depth
2
Block
3
Error total
Total variance 12
Treatment
5
Depth
2
Block
3
Error total
4
1
2
7
11
4
1
2
7
21.73
100.31
0.03
22.26
12.07
0.54
9.58
0.03
1.95
6.94 NS
6.94 SS
6.94 NS
6.94 NS
6.94 SS
6.94 NS
NS: Not significant at (p≥0.05)
SS: Significant difference at (p≤0.05)
The analysis of variance for soil bulk density, plant heights and plant leaf counts is given in Table 2. All
the interaction effects showed that there were no significant different (p≥0.05) in soil bulk density at 5%
level of significance. This result was in conformity with the findings of Franzen et al., (1994) who report
that in shallow soil with greater gravel content than deep soil, no differences were found in bulk density
among tillage operations. The analysis of variance for plant heights and plant leaf counts showed that
there were no significant different (p≥0.05) in treatments and blocks, while there were significant
different (p≤0.05) in depths at 5% level of significance.
12
Pant height cm
Figure 2 shows that plant height increased at an increasing rate with increasing bulk density, and then
increased at a reducing rate with increasing bulk density. However, from a bulk density of 1.90g/cm3,
there was a decline in plant height. The maximum Okra plant height of 860mm was obtained with
ploughed plus harrowed plot corresponding to bulk density of 1.90g/cm3.The regression equation
describing the relationship between the plant height and bulk density is given by y  19 .813 x  29 .411 .
The value of coefficient of determination R2 is 0.858. Increasing bulk density g/cm3, may lead to
compacting the soil which reduces growth of crop.
10
9
8
7
6
5
4
3
2
1
0
y = 19.813x - 29.411
R² = 0.8576
Series1
Linear (Series1)
1.75
1.8
1.85
1.9
1.95
Bulk density g/cm3
Figure 2. Effect of bulk density on okra plant height
Bulk Density g/cm3
The effect of bulk density on Okra plant leaf count at different tillage operations is shown in Figure 3.
There was decrease in bulk density with increasing plant leaf count. When the plant leaf count was 5, the
bulk density was 1.90g/cm3 and 1.78g/cm3 when the plant leaf count was 6. The plant leaf count is related
to the bulk density using linear regression equation given by Y  0.2111x  2.99. The coefficient of
determination R 2 is 0.501. The increasing plant leaf count as a result of decrease in bulk density may be
due to the fact that a low soil bulk density enhances the infiltration rate of the soil and hence an increase
in the water holding capacity of the soil. This, therefore, encourages better plant growth resulting in an
increase in plant leaf count.
1.94
1.92
1.9
1.88
1.86
1.84
1.82
1.8
1.78
1.76
y = -0.2111x + 2.99
R² = 0.501
5
5.2
5.4
5.6
5.8
Pant Leaf Count
Figure 3: Effect of bulk density on okra plant leaf count
13
The effects of tillage on Okra plant yield is shown in Figure 4. The highest number of seeds per plot,
number of fruits per plant, fruit weight , fruit length and fruit diameter were obtained in ploughed and
double harrowed treatments. This agrees with the finding of Rashidi and Keshavorzpour (2007) who
reported that the highest number of plants per hectare was obtained from conventional tillage, and notillage was the lowest.
30
Okra yields
25
20
15
Zero plot
10
5
0
Ploughed
plot
Ploughed +
harrowed
plot
Okra yields Performances
Figure 4. Effect of tillage treatments on okra yields
In the study of Kayombo et al., (2002) it was also reported that mouldboard and disc ploughing with three
harrowing produced the highest grain yields for both varieties of bean planted. Similar results were
reported elsewhere for maize (Gumbs and Summers, 1985).
The overall analysis for crop yield showed that conventional treatment had the highest values in all the
yield parameter which is therefore the best treatment for okra production. Ridged treatment, on the other
hand, had the lowest value of yield characteristics with poor or rather low yield performance.
The constants obtained for tillage operations and yield relationships in the regression equations of tillage
operations are given in Table 3.
Table 3. Regression equation parameters between various tillage operations and okra yield performance
Treatments
a
b
r2
Y (kg/ha)
To Zero plot
3.40
0.40
0.81
3.92
T1 ploughed plot
3.43
0.17
0.82
4.53
T2 Ploughed +
4.88
0.04
0.87
7.50
harrowed plot
T3 Ploughed +
5.97
0.23
0.96
17.69
harrowed +
harrowed plot
T4 Ridged plot
2.77
0.20
0.80
4.77
In zero tillage treatment, the regression coefficient b is 0.40 and is positive, while the correlation
coefficient (r2) is 0.81 and Okra yield is 3.92kg/ha. For the ploughed treatment, b value of 0.17, which is
regression coefficient, is positive and correlation coefficient (r2) is 0.82. There is a direct positive
14
correlation between plant height and number of leaf per plant, which means that as height of plant
increases, number of leaf per plant also increases.
Furthermore, when a is 3.43, it means that in ploughed treatment number of leaf per plant increases by
3.43 with height of plant, yielding to 4.53kg/ha value. For the ploughed and harrowed treatment, the, b
value of 0.04, indicates that the regression coefficient is positive, while correlation relationship (r2) is 0.87
and Okra yield (y) is 7.50kg/ha. This is a direct correlation relationship between plant height and number
of leaf per plant, which means that as height of plant increases, number of leaf per plant also increase in
ploughed and harrowed treatment. The value of a is 4.88 when yield is 7.50kg/ha. This indicates that
under ploughed plus harrowed plot treatment, number of leaf per plant increases by 4.88 with the height
of plant, yielding 7.50kg/ha for Okra performances.
Similarly, for the ploughed and double harrowed treatment, the b value of 0.23 shows that the regression
coefficient is positive, while coefficient of correlation (r2) is 0.96 and Okra yield is 17.69kg/ha. This is a
direct correlation relationship between plant height and number of leaf per plant, indicates that as height
of plant increases, number of leaf per plant also increases in ploughed and double harrowed treatments.
The a value of 5.97 when yield is 17.69kg/ha depicts increase of number of leaf per plant by 5.97 value
with the height of plant, yielding 17.69kg/ha of Okra under ploughed and double harrowed treatment.
Finally, for the ridged treatment, the b value of 0.20 shows that the regression coefficient is positive,
while correlation coefficient (r2) is 0.80 and Okra yield is 4.77kg/ha. This is a direct correlation
relationship between plant height and number of leaf per plant, which means that as height of plant
increases, number of leaf per plant also increase in ridged treatment. The value of a is 2.77 when yield is
4.77kg/ha. This depicts that under ridged treatment, number of leaf per plant increases by 2.77 with the
height of plant, yielding 4.77kg/ha for Okra yield.
From the regression and correlation analysis it was observed that the ploughed and double harrowed
treatment had the highest yield properties, while the ploughed and ridged treatments had relatively the
low yields for Okra production. This might be as a result of the fact that ploughed and ridged seedbeds are
not appropriate for Okra production, despite high level of soil pulverization involved in ridged treatment.
4. CONCLUSION
The research study evaluated the effect of no-tillage (zero), primary (ploughed), secondary (ploughed and
harrowed), conventional (ploughed and double harrowed), and ridged treatments on soil bulk density and
yields performance of okra. The different tillage treatments had no significant effect on soil bulk density.
The general results showed that conventional tillage treatment (ploughed and double harrowed) had the
highest yield of 17.69kg/ha thus indicating that it is the best treatment for Okra production. And zero
tillage had the lowest yield of 3.92kg/ha from regression analysis. This might be due to high level of bulk
density in the operation. This agreed with the results of Rashidi and Keshavarzpour (2007) that reported
crop yield of watermelon in the order of CT (Conventional tillage)> RT (Reduced tillage)> MT
(Minimum tillage)> NT (No-tillage). In the case of RT, MT and NT methods, the lower amounts of crop
yield obtained may be due to significantly greater soil bulk density which adversely affected ,root growth
and plant population density. On the whole, it was observed that soil bulk density property under
conventional tillage operation offered the best condition for Okra production.
REFERENCES
ASAE 30-22 ASAE standard 1965. Methods of soil analysis. Bulk density, Madison WI: ASA.
Aluko O. B. and Lassis D. 2009. Effect of tillage methods on some properties of tropical sandy loam soil
under Soybean cultivation. Proceedings of 3rd International conference of WASAE and 9th
International Conference of NIAE. Jan. 25-29, 2009, Ile- Ife, Nigeria.
15
Adeboye, O. C. and Oputa, C. O. 1996. Effects of galex on growth and fruit nutrient composition of Okra
(Abelmoschus esculentus). Ife Journal of Agricultural Engineering and Technology. Vol. 18(1&2) 19.
Ayotamuno, M. J., Zuofa, K., Ofori, A. S., and Kogbara, B. R. 2007. Response of maize and cucumber
intercrop to soil moisture control through irrigation and mulching during the dry season in Nigeria.
African Journal of Biotechnology vol. 6(5), pp 509-515.
Bauder, J. W., Randall G. W. and Swan J. B. 1981. Effects of four continue tillage systems on mechanical
impedance of a clay-loan soil sci. soc. Amer., 45 802-806.
Franzen, H., Lal, R and Ehlers, W 1994. Tillage and mulching effects on physical properties of a tropical
Alfisol. Soil Tillage Res. 28: 329-346 (ISI).
Gumbs, F. A. and Summers, D 1985.Effect of different tillage methods on fuel consumption and yield of
maize. Trop. Agric. (Trin), 62: 185-189.
Hakimi A. H. and Kachru R. P. 1976. Response of Barley Crop to different tillage treatments on
Calcareous Soil. J. Agric. Engng. Res (1976) 21, 299-403.
Hill, R. L. 1990. Long-term conventional and no-tillage effects on selected soil physical properties. Soil
Sci. Soc. Am. J. 54: 161-166 (ISI)
Kayombo B., Simalennga, T. E. and Hatibu, N. 2002. Effects of tillage methods on soil physical
conditions and yield of Beans in a Sandy Loam Soil.Journal of AMA, Vol. 33 No.4, 15-22
Khan F. U. H., Tahir A. R. and Yule I. J. 1999. Impact of different tillage practices and temporal factor
on soil moisture content and soil bulk density Int. J. Agri. Biol., 3: 163-166.
Khurshid K., Igbal M., Arif M. S. and Nwaz, A. 2006. Effect of tillage and mulch on soil physical
properties and growth of maize. Int. J. Agri. Biol. 5:593-596.
Lampurlanes, J. and Cantero-Martinez, C. 2003. Soil bulk density and penetration resistance under
different tillage and crop management systems and their relationship with Barley root growth.
Agronomy Journal 95: 526-536 American Society of Agronomy.
Lal R. 1993. Tillage effects on soil degradation, soil resilience, soil, quality and sustainability. Soil and
Tillage Res 51:61-70.
Markose, B. L. and Peter, K. V. 1990. Okra review of research on vegetable and tuber crops. Technical
Bulletin 16. Kerala Agricultural University press Mannutly, Kerala, 109pp.
Nkakini S. O., Akor, A.J., Fila I. J. and Chukwumati, J. 2008. Investigation of soil physical property and
Okra emergence rate potential in Sandy Loam soil for three tillage practices. Journal of Agricultural
Engineering and Technology (JAET), volume 16 (No.2) December, 200.
Nwagu A. N. and Oluka S. I. 2006. Optimum tillage system for Okra production in all ultisol of South
Eastern Nigeria. Journal of Agricultural Engineering and Technology (JAET) vol, 14, 79-85.
Rashidi M. and keshavarzpour F. 2007. Effect of different tillage methods on grain yield and yield
components of maize (zea mays L.) Int. J. Agri. Biol. 2/; 274-277. Sci soc. A J.57:1586-1595.
Siemonsma, J. S. 1982. The cultivation of okra (Abelmoschus SPP), tropical fruit vegetable (with special
reference to the Ivory Coast) D.H.O. Thesis Wagemingen Agricultural Wagemingen, the Netherlands.
16
DESIGN OF A LOW-COST COCOA OIL EXPELLER
O. S. Ogundipe, S. I. Obiakor, F. B. Olotu, O. A. Oyelade and J. A. Aransiola
National Centre for Agricultural Mechanization (NCAM), Ilorin, Nigeria.
ogundipeolusanya@yahoo.com
ABSTRACT
At the National Centre for Agricultural Mechanization (NCAM), Ilorin, the design of a locally made lowcost cocoa oil expeller has been conceived. In order to design this low-cost cocoa oil expeller, some
design criteria such as capacity (processing 1.5 tons of cocoa bean per day), low maintenance cost, ease of
operation, easy of fabrication, use of locally available material, ease of assembly and disassembly of
component parts, rigidity, durability and portability were considered. The machine consists of hopper,
body frames, screw worm shaft, barrel, cake adjustable out-let, oil discharge outlet, belt and pulley drive,
speed reduction gear and 40 hp electric motor. The processing of cocoa bean through local means is seen
as a means of reducing importation bills obtained from the importation of cocoa oil expeller into the
country. For this reason, there is need to encourage the development of locally made cocoa oil expeller in
Nigeria.
KEYWORDS: Cocoa, butter, expeller, oil, cake
1. INTRODUCTION
Raw, fermented and dried cocoa bean was a major foreign exchange earner for Nigeria in the olden days
before the advent of petroleum exploitation. The quantity of oil and butter derived from the processing of
1 ton of cocoa bean alone is more than the total quantity obtained from raw cocoa bean that is exported.
Cocoa in the world market refers to the cocoa tree (theobroma cacao lin) that have been fermented and
properly dried. Nigeria used to be the biggest producers of cocoa in the world with a production of
200,000 – 300,000 tons per year (Ogutuga and Williams, 1975).
Nigeria like most cocoa producing countries exports most of the cocoa bean to the United State and other
European countries where it is processed into cocoa oil, butter, chocolate, cocoa powder and other cocoa
confectionaries. Cocoa is native of the humid low lands of Tropical America. Wild types have been
reported in the Amazon and Orinoco rivers (Backer and Hard, 1975).
In the production of cocoa oil/butter and other cocoa products, cocoa nib which is the inner part of cocoa
bean is the most valuable portion which is of commercial importance. The initial process in the
production of the cocoa beans are the grinding of the dehulled cocoa beans with the cocoa nibs into a
thick paste which can be further pressed to remove most of the oil called “cocoa oil”. The resultant cake
could be pulverized and grind to give “cocoa powder”. Oil can be extracted, from nuts and seeds by heat,
solvents or pressure. Extraction by heat is not used commercially for vegetable oils (Casten and Snyder,
2001). Pressure extraction separates the oil from the solid particles by simply squeezing the oil out of the
crushed mass of ground seeds.
The simplest method is to fill a cloth bag with the ground seed pulp and hang the bag so that it can drain.
Some of the oil, called free oil flows out, the rest must be pressed out mechanically. The simplest way is
by placing heavy rocks on the materials or bags of oil seed pulp can be placed on top of each other in a
box or cylinder, and great pressure can be slowly applied on the whole mass. A long lever can exert up to
4.58kN. Since great pressure provides greater oil recovery, heavy and strong mechanical jacks of several
designs (screw jacks, ratchet jacks and hydraulic jacks) have often replaced the lever (Casten and Snyder,
2001). Use of hydraulic jack pressure developing system can also be used in the place of placing heavy
mass on the bags. There are wet rendering processes as well as the cage methods of extracting the oil. The
other two main methods of oil extraction are solvent and mechanical screw press methods (Mrema and
17
McNulty, 1985). The first two methods are more labourious, time consuming and less effective, while the
last two methods expel oil more efficiently. Therefore, most of the commercial oil extraction is done with
mechanical screw press known as expeller.
Oil expeller has been described by UNIFEM (1987) as an equipment consisting of a horizontal rotating
metal worm screw, which feed oil bearing raw materials into a conical barrel-shape with perforated wall
and as a result of the pressure developed in the barrel, oil is extracted. The solvent extraction method
involves milling of the kernel, pressing the meal and dissolving the cake in some appropriate solvent e.g.
Hexane. The oil-solvent mixture is filtered off, while the cake and the solvent are later evaporated to
recover the oil.
The screw press method involved the feeding of the pre-heated kernels into the screw mechanism made of
an interrupted helical thread (worm), which revolves within a stationary perforated cylinder called the
cage or barrel. The fed kernels are ferried through the barrel by the action of the revolving worms. The
volume axially displaced by the worm diminishes from the feeding end to the discharge end, thus
compressing the meal as it passes through the perforation of the lining bars of barrel, while the de-oiled
cake is discharged through an annular orifice. Mechanical oil expression (rig) equipment is designed for
optimum performance in order to meet specific usage.
Ogutuga and Williams (1975) reported that Nigeria cocoa industries processed 23,000 tons of cocoa into
the cocoa oil for export. This process produced sizeable quantity of cocoa powder, some of which were
used locally in the manufacture of beverages like bournvita, ovaltine, cake con-food, cocoa bread etc.
Nigeria will prefer consuming more cocoa products that are locally produced. Among such products is
cocoa bread, biscuit, cocoa portage, cocoa wine, cocoa butter and cocoa powders. Moreover, cocoa jelly
has also been synthesized from cocoa bean (Mensah, 1975). Figure 1 shows the flow chart of cocoa bean
processing. The cocoa processing industries that were established in Nigeria in the past such as Cadbury
Nigeria Limited produced all the aforementioned cocoa products. Most of these established cocoa
processing industries in Nigeria went out of production due to the change in government policy.
However, during Obasanjo’s administration, the policy on agricultural development shifted back to cocoa
production and several efforts have been made towards revamping cocoa production compared with
previous years when cocoa contributed to the country’s foreign exchange earnings in the non oil sector.
18
Harvesting of Cocoa Pods
Breaking of Cocoa Pods
Key
Operation
Product
Fermentation
Washing
Fermentation
entation
Drying
Cleaning
Extraction of Cocoa Juice
Roasting
Dehulling of the Cocoa beans
Addition of Preservative
/Addictive
Grinding of dehulled Cocoa beans
(To facilitate easy
removal of Oil)
Alkalinization
Pressing
Wine Cocoa Wine
Cake
Crude Cocoa Oil
Pulverize
Filtering
Milling
Cocoa Powder
Cocoa Oil
Figure 1. Flow chat of cocoa beans processing (Source: CRIN (1985))
19
The processing of cocoa locally is seen as a means of reducing the import bills on these products and thus
saves the country lots of money obtained through foreign exchange for use into other cogent needs of the
Nigerian economy. In view of the economic value of cocoa products to the people, there is urgent need to
improve and develop a prototype cocoa oil expeller for processing cocoa bean to cocoa oil which is
generally called cocoa butter after solidification. The cocoa oil expellers available in Nigeria today are of
the imported type equipped with sophisticated technology for handling. These features of this machine
alone make the machine very expensive for an average individual to purchase. Therefore, there is need for
the design of a low-cost locally made cocoa oil expeller for use in the country which every single
household in Nigeria could afford.
This paper describes the design and operation of a new cocoa seed oil expeller.
2. DESCRIPTION OF COCOA OIL EXPELLER
The cocoa oil expeller consists of three main units, namely, feeding, milling and discharge units (Figs. 2,
3, 4). Other component parts of the oil expeller are hopper, frame, belt and pulley drive, screw worm
shaft, barrel, perforated sieve, oil discharge outlet, cake discharge outlet. The frame of the designed cocoa
oil expeller is made of mild steel H-channel bar. The expeller is powered by a 40 hp electric motor via
speed reduction gear.
2.1 Hopper Capacity
The hopper is a frustum of pyramid (a pyramid with a portion of the head cut off parallel to the base).
The volumetric capacity is given as
=
+
+
+
ℎ
(1)
where,
= Areas of top and bottom base of the hopper
,
1
= 0.146 + 0.090 + √0.146 + 0.090 0.380
3
V = 0.091 m3
2.2 Force Imposed at the Seed Net Point
Maximum mass of the seed to be processed at a time is 25 kg.
Using the force equation =
(2)
where,
F = Force (N), m = Mass (kg), g = Acceleration due to gravity (m/s2)
F = 25 x 9.81
F = 245.25 N
This implies that in addition to the weight of the worm shaft, the seed will impose an additional force of
245.25 N at the seed net point.
2.3 Torque on Shaft
Torque developed on shaft is calculated as
where,
=
/
(3)
Ρ = Maximum power input the motor (W), n = Rotation speed (rad/s)
20
The shaft is powered by a 40 hp (30 kW) electric motor.
Maximum speed expected to be transmitted to the shaft = 45 rpm
T = 30 x 103/4.71
T = 6369.43 Nm
2.4 Design of the Worm
Let the helix angle of the worm = λ
Let the circular pitches in the planes of rotation for worm and reduction gear = p1 and p2 respectively.
Let the circular pitch normal to the direction of the reduction gear = pn
Then p =
sin =
cos
(4)
Equation (4) should be divided through by Π and Π/pn replaced by pdn, the normal diametric pitch to give
pdn = / sin = cos
(5)
Let N1 be the number of crest of the worm, and N2 be the number of teeth in the reduction gear,
respectively.
Now
=
. The value of P1 from equation (4) can be substituted to give
=
/
(6)
For the purpose of this design, the worm will have eight crests and an assumed pitch of 1 inch (25 mm).
Then the diameter of the worm could be determined using
=
(7)
/ /
d1 = 8 x 25 = 63.653
3.142
A worm of diameter 69 mm was machined for the oil expeller.
2.5 Shaft Design
By virtue of design of this oil expeller, the worm will have to be machined on the shaft. There is a need
for an original (parent) shaft design which will later bear the worm. The design of the shaft is based on
strength and will be controlled by maximum shear theory. By applying the maximum shear equation, the
shaft shall be designed by using ASME code equation of solid shaft expressed in equation (8)
=
(
) +(
)
(8)
where,
d = diameter of the shaft (m), kb = combined shock and fatique factor applied to bending moment,
Kt = combined shock and fatique factor applied to torsional moment, Ss = Allowable shear stress
for the shaft (Mpa)
Tolerance of 0.5 mm between the shaft and the housing barrel of internal diameter 70 mm.
2.6 Length of Keyway
The width and depth of the keyway is selected from the standard keyway dimension used by PAN (2009),
which stated that for a shaft of 70 mm diameter, the recommended standard keyway dimensions for width
and depth should be 20 mm and 12 mm, respectively.
21
In the design of key it may be based on the shear and compressive stresses induced in the key as a result
of the torque being transmitted. Therefore to determine the length of keyway, the expression used by Hall
et al. (1961) for calculating the length of keyway is given as
Ss = F/bL
(9)
where,
Ss = Allowable shear stress (Mpa), F = Force exerted on the keyway (N), b = Width of keyway
(m), L = Length of keyway (m)
Recall from equation (3) that Torque was calculated as 6369.43Nm
The relationship between Torque and Force exerted on the keyway is given as
T = Fr
where,
T = Torque on shaft (Nm), F = Force exerted (N), r = radius of shaft (m)
(10)
from equation (10) F = 90.992kN when r = 0.07 m
Substituting in the values of 100 MPa, 90.992 kN and 0.02 m for Ss, F, b, respectively into equation (9)
L = 0.045 m (45 mm)
2.7 Volume of Compression Barrel
The compression barrel is 410 mm in length with an internal diameter of 70 mm. The volume of the barrel
is given as
=
(11)
where,
V = Volume required (mm3), r = Radius of barrel (mm), l = Length of barrel (mm)
V = π (352 x 410)
Therefore, V = 1,578,500 mm3
2.8 Forces Acting on the Barrel
Cocoa oil expelling machine is an important device for oil recovery from cocoa beans by crushing the
cocoa beans inside the barrel with direct firing of barrel and the cocoa oil is being pressed out as a result
of the pressure built inside the barrel. Generally, the barrel behaves like a simple pressure vessel – the
cylindrical shell, computed on the assumption that the stress is uniform throughout the wall thickness.
Thus, circumferential or hoop stress σh and longitudinal stress σl is given by:
σh = f = Prl = Pr
(12)
tl tl t
and σl = πr2p = Pr
2πrt 2t
(13)
where,
f = Hoop force (N), t = Thickness of the cylindrical wall (m), l = Length of the cylindrical wall
(m), P = Intensity of the internal pressure (N/m2), r = Internal radius of the cylindrical wall (m).
2.9 Speed of Expellant Shaft
The ratio of the pulley for the electric motor to that of the expellant shaft was calculated as given by
Olaomi (2008) as:
22
N1D1=N2D2 (14)
where,
N1 = Speed of the driving motor (rev/min), N2 = Speed of the expellant shaft (rev/min), D1 =
Diameter of driving pulley (m), D2 = Diameter of driven pulley (m)
The calculated speed of the expellant shaft was obtained as 270 rev/min.
2.10 Speed and Length of Belt
The belt speed V (m/s) and its total length L (m) were calculated as given by Khurmi and Gupta (2004)
respectively as:
V = πN1D1
60
(15)
and L = π(D1 + D2) + 2C + (D1 – D2)2
(16)
2
4
where,
V = speed of belt (m/s), L = Total length of belt (m), N1 = Speed of the driving motor (rev/min),
D1 = Diameter of driving pulley (m), D2 = Diameter of driven pulley (m), C = Pulley centre
distance (m)
By substituting in the values of D1 = 250 mm, D2 = 50 mm, and C = 400 mm, the calculated values of V
and L are 3.67 m/s and 1296.24 mm, respectively.
The isometric view, orthographic projection and exploded view of the NCAM Low-cost Cocoa Oil
Expeller are presented in Figures 2, 3 and 4, respectively. The bill of engineering materials is presented in
Table 1.
Figure 2. Isometric View of Cocoa Seed Oil Expeller
23
Figure 3. Orthographic Projection of Cocoa Seed Oil Expeller
Figure 4. Exploded View of Cocoa Seed Oil Expeller
24
Table 1. Bill of Engineering Measurement and Evaluation (BEME) for Low Cost Cocoa Oil Expeller
S/N. Component part
Material
Qty
Rate
Amount
specification
(N)
(N)
1.
Main frame
Structural steel
4 length
3,500
14,000
u-channel 4”
2.
Electric motor
40 Hp
1
80,000
80,000
3.
Prime mover stand support
u- channel 4”
2 length
3,500
7,000
4.
Bevel spiral Gear reduction
30 Torque Ratio 1:6
1
40,000
40,000
5.
Body cover of the machine
Galvanized sheet
4 sheets
3,500
14,000
6.
Pillow bearing
Ø70 mm bore
2
3,000
6,000
proprietary
7.
Pulley
Double grooved
2
3,000
6,000
8.
Riveting pins
Mild steel
1 set
3,500
3,500
9.
V-Belt
A52
1
1,200
1,200
10.
Bolts and nuts
Mild steel
2 dozen
1,000
2,000
11.
Electrode
Gauge 10
2
4,500
9,000
12.
Sleeve & perforated plate
2 mm stainless
2 sheets
5,000
10,000
13.
Grinding disc and plate
Disc and plate
4
350
1,400
14.
Screw stainless and machining Ø70 mm rod
½ length
35,500
35,000
15.
Computer AutoCAD drawing
Drawings
2
7500
15,000
16.
Twist drill
Ø6mm, Ø8mm &
1 set
3,500
3,500
Ø12mm
17.
Heater band and temperature 12 KVA
3 sets
14,000
42,000
control
18.
Transportation for conveying
Lump
8,000
8,000
fabricated material
Total
N 297,600
3. CONCLUSION
At the National Centre for Agricultural Mechanization (NCAM), Ilorin, the design of a locally made lowcost cocoa oil expeller has been conceived for possible adoption by our local fabricators in Nigeria who
are capable of mass producing this equipment for use.
REFERENCES
Baker N. R. and Hards W. K. 1975. Biological and Physiological Aspect of Leaf Development in Cocoa
Theobroma cacao Vol. 72: 1315-1324.
Casten, J. and Snyder, H. E. 2001. Understanding Pressure Extractions of Vegetable Oil. Attra Small
Scale Oil Seed Processing. P. 11 – 18.
CRIN 1985. Cocoa Research Institute of Nigeria 1985 advisory leaflet, Ibadan Oyo State.
Hall, A. S., A. R. Holowenko and H. G. Laughin 1961. Schaum’s Outline of Theory of Problems of
Machine Design. Schaum’s Outline Series, McGraw-Hill.
Khurmi, R. S. and Gupta, J.K. 2004. Theory of Machines, Eurasia Publishing house, New Delhi, India
Mensah, F. A. 1975. Cocoa Processing in Developing Countries, Problems of Establishment and
Development. Paper Presented at International Conference on Cocoa Economic Research, Legon.
Mrema, G. C. and McNulty, P. M. 1985. Mathematical model of mechanical oil expression from oil
seeds. Journal of Agricultural Engineering Research, 31 (5), 361 – 370.
Ogutaga D. B. A. and Williams S. O. A. 1975. Development of New Products as a Method of Increasing
the Consumption of Chocolate and Other Cocoa Products in Nigeria. (Cocoa International Conference
1975) Vol. Pg. 55 – 66.
Olaomi, J. 2008. Design and Construction of a Motorized Groundnut oil Expelling Machine. B. Eng
Thesis, Department of Mechanical Engineering, University of Ilorin, Nigeria
25
PAN 2009. Product Application Notes. Vol. 56 (3): 17656-3. Available at
http://www.gates.com/ptpartners/file_display_common.cfm?thispath=Gates%2Fdocuments_module&
file=Vol_56_No_3-Shaft_And_Hub_Keyway_And_Key_Sizes.pdf.
UNIFEM 1987. Oil Extraction by UNIFEM Intermediate Technology Publications.
26
DEVELOPMENT AND PERFORMANCE EVALUATION OF A DOUGH
KNEADING MACHINE WITH ADJUSTABLE NIP
U. N. Onwuka1, O. A. U. Okafor-Yadi2 and N. P. Njiuwaogu
Department of Agriculture and Bioresource Engineering,
Michael Okpara University of Agriculture, Umudike, Nigeria
1
unonwuka@yahoo.com, 2ossey2a@yahoo.com
ABSTRACT
A dough kneading machine with adjustable nip was designed and constructed on a 5000 x 6000 x
8000mm stand with a galvanized iron sheet top cover and driven by a 2hp electric motor. The nip
clearances achieved were 0.02, 0.04, 0.06, 0.08 and 0.10mm between the kneading rollers. One on the
rollers was made stationary while the other is being adjusted; the adjustment was by the action of both
and nut assembly at both ends of the roller. The kneader was tested with 15kg of both wheat and cassava
for both manual and electrical operation respectively. The performance was tested by comparing the
kneading rates, the thickness of kneaded dough and temperature after kneading between the manual and
the electrical runs, for both cassava and wheat dough. The result obtained showed that kneading rate for
manual operation lies between 22.09 - 34.8Kg/hr and 21.43 – 33.33Kg/hr for wheat and cassava
respectively. Also the kneading rate for electrical operation lies between 115.38 – 187.50Kg/hr and 71.43
– 168.51Kg/hr for wheat and cassava respectively. And that the thickness of kneaded dough for manual
operation lies between 0.031 – 0.10cm and 0.041 – 0.10cm for wheat and cassava respectively. Also the
kneading rate for electrical operation lies between 0.037 – 0.131cm and 0.052 – 0.143cm for wheat and
cassava respectively. The temperature for the wheat remained relatively around the room temperature
with the electrical run rising to 33oC when the nip clearance was reduced to 0.02cm. the temperature of
the cassava dough for manual run dropped to 32oC while that of the electric run dropped to 38oC showing
a greater loss in temperature for the manual operation as a result of longer kneading time used. It was
therefore concluded that the fabrication of a dough kneader with adjustable nip is feasible and that the
machine gave a more even dough thickness at manual run while the final temperature for the cassava
dough was best with electrical operation. However, the electrical operation gave a greater output for both
cassava and wheat dough.
KEYWORDS: Dough kneader, adjustable nip, snacks consumer avarice
1. INTRODUCTION
Kneading is the art of pressing a mixture of flour and water several times thus making the dough elastic in
texture. Feller and Beon (1988) stated that the process (Kneading) makes the gases escape from the dough
making it easier to shape. Hoseney (1994) showed as well that dough kneaders redistribute yeast cells
giving them fresh sugar and starch molecules to feed on as fuel for the second rising.
Dough kneading in the time past are done with hand, feet, or smooth rolling wood. Jeffery and Naomi
(2003) stated that although Kneading can be done by machine (using a stand mixer fitted with dough
hook) home bakers have traditionally kneaded by hand.
The increased tendency among children and adults to move away from traditional eating pattern of three
meals a day to eating snacks instead of meal, and the increased number of fast food centers emphasizes
the need for more dough kneading machines. Efficient kneading of the flour dough has become a major
consideration. Eke (2001) also stressed that “Kneading (pressing) are the most tedious and essential
operations in modern baking industries hence effort should be concentrated on this task.
It is clear that a number of agro machines are available for food processing but they have limitations.
Some local efforts in recent times to mechanize dough kneading by research institutions locally are
27
among the numerous attempts in meeting this challenge this includes the development of dough kneaders
by National Root Crop and Research Institute Umudike, Nigeria. This design gave dough a good texture.
Its limitation was that the thickness of the dough produced cannot be adjusted. Also Yista, et al (2006)
developed a dough kneading machine in FUT Minna and they recommended for further work that an
adjuster for the gap between the rollers be provided.
Most locally fabricated dough kneading machine which are constructed by the road side welders are done
without proper design specification, alignment of parts and with no adjustable nip. The once imported are
too expensive and are not affordable to small scale food processors and when they can afford them the
problem of durability, in adherence to operation manual, lack of spares and poor maintenance culture sets
in. It is therefore desirable that an alternative be developed hence this work advocates the development of
a kneader with adjustable nip and evaluate the performance. This will help to create product variety and
meet consumer avarice.
The objectives of this work were to: develop a dough kneading machine, introduce an adjustable nip for
varying dough thickness and evaluate the performance of the dough kneading machine.
2.1 Design Consideration
The dough kneading machine involved the use of compressive force in moving dough in between two
rotating dough rollers. Hence, in this work it was necessary to first establish the following parameters
from available literature.
i. Rheology of dough
ii. Pressing capacity
iii. Fed rate of a minimum of 50kg/hr
iv. Minimum desirable thickness of dough for confectionary use
v. And the minimum pressure required compressing normal dough.
2.2 Design Assumptions
The following assumptions were made:
i.
The dough is a typical Non-Newtonian fluid hence
Where; = ℎ
.
=
ℎ
and
=
…………………………………..1
=
ii. The cohesion between the molecules of the dough is much greater than it adhesion to metal.
iii. The shear stress of dough = 7074 N/m2 density of dough = 1,330 kg/m3 (Yisa et al 2006)
2.3 Design Theories
The active components of the dough kneading machine are the press rollers and the adjustable nip. These
components were designed based on the following theory.
The transmitted torque from driven pulley shaft is calculated from
=
×
………………..………(2)
(Khurmi and Gupta, 2005)
= 22 7(constant)
Given a power of 746w = 1Hp motor T is therefore 23.7N/M
The power transmitted by shaft is given by
Where N2 = speed of shaft in rpm
28
(
)=
×
=
……………………… (3)
(Khurmi and Gupta, 2005)
Where rpm. = revolution per min of the shaft,
T = torque
Dough Flow Rate
( )⨉
ℎ
( )=
(Rajput, 2000)
( )
The area of the orifice is given by the length of the roller multiply by the distance between the two rollers
Hence the flow rate is given by ( × +
) ….. (4)
2.4 Design of the Roller
Density of steel is given as 7850Kg/m3 Kurmi and Gupta (2005). Thickness of the external cylinder of the
of the roller t= 3mm, diameter = 50mm
Volume ( ) = [
L] − [ ( − ) L] , ……............................ (5)
Where L = length of the roller, r-radius of the roller.
Mass of the roller is given by
=
( )×
( )
Weight is given by
=
×
Dough kneading can be viewed as a rolling process (Yisa et al, 2006)
The rolling force can be determined by =
………. (6)
(Yisa et al, 2006)
Where
= shear stress of the material (N/m2)
F = force of rolling
L = length of contact of material and roller given by (ℎ − ℎ )
W = width of material (in mm)
hi = clearance between the two rollers (in mm)
ℎ = 2 + ℎ =distance between the center of the two rollers.
2.5 Design Adjustable Nip
The adjustable nip was made from a combination of bolts with matching nuts this served as a support to
the upper roller see figure 1. The following parameters for the bolt and nut used for the nip were
determined:
The shear stress across the threads is gotten from
=
………………………………………………………… (7)
× ×
Where b = width of the thread section at the root. (mm)
dc = Minor or core diameter of the thread (mm)
T = torque applied
P = maximum safe axial load. (Khurmi and Gupta 2005)
The thread shear stress ( ) for the nut is gotten from
=
× ×
……………………………………………. (8)
29
Where d = major diameter (Khurmi and Gupta 2005)
Load on the bolt is given by
=
×
× ×
or
=
……………. (9)
d = major diameter of the bolt and
n = number of bolts
= torsional shear stress (Khurmi and Gupta 2005)
Table 1 shows the design specification for the bolt and selected for the construction of the nip adjustment.
Design dimensions of screw thread for bolt and nut used according to IS: 4218 (part III) 1976 (reaffirmed
1996)
Designation Pitch Major or nominal
Effective or
Minor or core
Depth of
Stress
(mm) diameter of nut
pitch diameter
diameter
the tread
area
and bolt d=D
nut and Bolt dp Bolt
(bolt mm) (mm2)
Nut
(mm)
(mm)
M 16
2
16.000
14.701
13.546 13.835 1.227
157
(Source Khurmi and Gupta 2005)
2.6 Description of the Kneader
An orthographic view with an insert of isometric drawing of the dough kneader is shown in figure 1 and
the exploded front view of the adjustable nip is shown in Figure 2.
Figure 1. Orthographic views with Isometric Insert of the machine
30
Figure 2. Adjustable Nip
The equipment is a one unit fabricated machine. It achieves the dough kneading by the passing the dough
between two rollers which rotate in opposite direction driven by two spur gears. In this design the top
roller carries the adjustment nut and bolt mechanism. The adjustment is achieved by screwing the bolt on
the nut until required clearance is achieved. The drive is taken by the down roller from a 2hp electric
motor via a v-belt. Loading of the dough is manual.
2.7 Experimental Procedure for Testing
The crop materials used for the production of flour used for the test are wheat (Triticum aestivum) and
cassava (Manihot spp). The choice of wheat was informed by the fact that it presently the most popular
cereal grain, for production the production of bread, and other pastries (Ihekoronye and Ngoddy, 1985).
Cassava was also chosen as a result of its local availability. The ambient temperature was measured using
a thermometer. Then the two samples of cassava and wheat flour was respectively mixed with water to
form dough. The wheat was mixed with water at room temperature for 8.18 minutes, while that of the
cassava flour was mixed with water at 60oc for 10.2 minutes (the cassava flour was mixed with warm
water to allow for efficient mixing and kneading). 15kg of the wheat dough was weight out and passed
though the dough kneader run with a 2Hp electric motor at an rpm of 600, a stop watch was used to
determine the time used for thorough kneading. The thickness of the dough kneaded dough was measured
using a micrometer screw gauge the temperature before and after kneading was also determined using a
thermometer. This experiment was carried out five times with the adjustment on the nip placed at 0.02,
0.04, 0.06, 0.08, and 0.10 (mm). The same test was done using the cassava dough. The procedure above
was repeated with the machine operated manually. The performance was evaluated based on the
following;
ℎ
=
……………………………………. (10)
=
× 100%........... (11)
31
3. RESULT AND DISCUSSION
3.1 Results
Table 2 and 3, Figure 3 show results of performance tests on the kneader.
Table 2. The result of test carried out on the machine using wheat flour
Nip
Time for
Mass kneaded
Kneading rate
Thickness of
adjust
kneading
Kg
Kg/hr
kneaded dough
ment
(hr)
cm
cm
manu Electri manu electri Manu Electri manual Electri
al
cal
al
cal
al
cal
cal
1st 0.10
0.43
0.08
15
15
34.88 187.50 0.100
0.131
nd
2
0.080
0.54
0.089
15
15
27.79 168.54 0.080
0.084
3rd 0.06
0.59
0.099
15
15
25.42 151.52 0.061
0.069
4th 0.04
0.65
0.12
15
15
23.08 125.00 0.048
0.053
th
5
0.02
0.67
0.13
15
15
22.39 115.38 0.031
0.037
Table 3. The result of test carried out on the machine using cassava flour
Nip
Time for
Mass
Kneading rate
adjustm
kneading
kneaded
Kg/hr
ent
(hr)
Kg
cm
manua Electri manu electr Manua electrica
l
cal
al
ical
l
l
1st 0.10
0.45
0.089
15
15
33.33
168.51
2nd 0.080
0.55
0.096
15
15
27.27
156.25
3rd 0.06
0.63
0.13
15
15
23.81
115.38
4th 0.04
0.66
0.16
15
15
22.73
93.75
th
5
0.02
0.70
0.21
15
15
21.43
71.43
Thickness of
kneaded dough
cm
Manua
l
0.100
0.080
0.064
0.051
0.041
Electri
cal
0.143
0.089
0.072
0.060
0.052
Temperature of
kneaded dough
(oc)
Manu
al
31
31
31
31
31
Electri
cal
31
32
32
32
33
Temperature
of kneaded
dough
(oc)
Man electri
ual
cal
41
52
39
49
39
45
35
42
32
38
1.2
efficiency÷100
1
0.8
0.6
0.4
0.2
0
.10m
.08m
.06m
.04m
.02m
wheat manual
1
1
0.98
0.833
0.64
cassava manual
1
1
0.93
0.78
0.48
wheat elect
0.763
0.952
0.869
0.755
0.54
cassava elect
0.69
0.899
0.833
0.666
0.38
Fig 3 Machine Dough Sizing Efficiency Result
32
3.2
Discussion
From table 2 it is seen that the result of the test showed that the kneading rate for the wheat dough
increased as the roller clearance (as a result of the nip adjustment). It increased progressively for both the
manual run and the electric motor run. It was also observed that the dough thickness for the manual run
increased more steadily than that of the electric motor run. The result from table 3 showed a similar result
for the cassava dough. Although, the result from the electric motor run showed a less steady progression.
This may be as a result of the difference in the rheological property of cassava when compared to that of
wheat The rheological properties of starchy materials are dependent on temperature and so the higher the
temperature the more likely will the dough become more viscous hence restrict the driving force. Cassava
products have high swelling power than wheat (Ihekoronye and Ngoddy, 1985)
The summary of the result as shown in table 2 and table 3 showed that kneading rate for manual operation
lies between 22.09 - 34.8Kg/hr and 21.43 – 33.33Kg/hr for wheat and cassava respectively. Also the
kneading rate for electrical operation lies between 115.38 – 187.50Kg/hr and 71.43 – 168.51Kg/hr for
wheat and cassava respectively. And that the thickness of kneaded dough for manual operation lies
between 0.031 – 0.10cm and 0.041 – 0.10cm for wheat and cassava respectively. Also the kneading rate
for electrical operation lies between 0.037 – 0.131cm and 0.052 – 0.143cm for wheat and cassava
respectively. The temperature for the wheat remained relatively around the room temperature with the
electrical run rising to 33oC when the nip clearance was reduced to 0.02cm. The temperature of the
cassava dough for manual run was 32oC while that of the electric was 38oC showing a greater energy
utilization as a result high kneading capacity.
The result from the dough sizing efficiency chart was formulate as shown by the chart in figure 3 the
chart showed that the dough sizing efficiency of the machine was relatively high. The optimum efficiency
was obtained for both wheat and cassava in both the electric motor and manual run, when the nip
adjustment was at the 0.08m adjustment point. And least at the 0.02m adjustment point. The efficiency
decreased as the clearance decreased, this is because a greater clearance allows freer and faster flow of
dough. The possibility of producing dough with variable sizes gives processors of meat and fish pies and
other confectioneries the opportunity to satisfy the taste and demand of various consumers.
4.
CONCLUSION
Based on the result of this work the locally made dough kneader with adjustable nip performed
efficiently, when introduced to the local industry it will reduce most of the problem that local
confectionary outlets has faced with previous versions of locally made kneaders that produced only
specific thickness of dough. It is also of note to state that an objective data collection and comparative
analysis of the various versions of kneaders if carried out will help advice researchers on the quality of the
product processed by these locally made machines.
REFERENCES
Eke O. U. Ibid 2001. Chemical Evaluation of Nutritive Value of Some Nigerian Foods
Feller D. A. and Beon, M. M. 1988. Composite Flour. Food Review Inta. Vol. 14 (2).
Hoseney, R. C. 1994. Yeast Leavened Products in Principles of Cereal Science and Technology; St. Paul
M. N. American Association of Cereal Chemist 2nd Edition.
Ihekoronye A. I. and Ngoddy, P. O. 1985 Integrated Food Science and Technology for the Tropics.
Macmillan Educational Limited, London.
Jeffery A. and Naomi D. 2003. Home Baking. Artisan, New York
Khurmi R. S. and Gupta, J. K. 2005. A Textbook of Machine Design. Fourteenth Edition; Eurasia
Publishing House (PVT.) LTD. Ram Nagar, New Delhi.
Rajput, R. K. 2000. A Textbook of Fluid Mechanics. Third Edition S. Chand and Company Ltd. Nagar,
New Delhi.
33
Yista et al, 2006. Development of a Dough Kneading Machine Proceedings of Nigerian Institution of
Agricultural Engineers Volume 28, 94 – 97.
www.cmis.csiro.au/doughreology/htm
34
DEVELOPMENT OF METAL-IN-WALL EVAPORATIVE COOLING SYSTEM FOR STORING
PERISHABLE AGRICULTURAL PRODUCE IN A TROPICAL ENVIRONMENT
F. R. Falayi and A. O. Jongbo
Department of Agricultural Engineering,
Federal University of Technology, Akure, Ondo State, Nigeria.
folayanrichard@yahoo.com or frfalayi@futa.edu.ng
ABSTRACT
The problem of storage of perishable agricultural produce cannot be overemphasized in a developing
country like Nigeria. To reduce the level of deterioration of produce at village level, a metal-in-wall
evaporative cooling chamber was developed using bricks and seabed sand. The evaporative cooling
system was constructed with local ram materials, uses the natural cooling system and does not require
electrical or mechanical energy. Storage trials were conducted with tomatoes and vegetable leaves.
Temperature and relative humidity of the evaporative cooling system chamber and the ambient storage
were measured and recorded for eight days. Weight loss of the produce and visual observations were
carried out to determine the level of deterioration of the produce. It was discovered that the cooling
chamber had an average temperature drop of about 7° C when compared with the ambient temperature
and an average relative humidity drop of about 4% was experienced throughout the period of the study.
The percentage weight loss in the cooler was 4% and 17% for tomatoes and amaranthus respectively
while the percentage weight loss in ambient storage condition was found to be 24% and 74% for tomatoes
and amaranthus respectively. The metal-in-wall evaporative cooling system is efficient and can
successfully store fruits and vegetables for 6 to 8 days without any visible deterioration.
KEYWORDS: Temperature, relative humidity, metal-in-wall, seabed sand, storage, post harvest loss,
evaporative cooling.
1. INTRODUCTION
Much of the post-harvest loss of fruits and vegetables in developing countries is due to lack of proper
storage facilities. Vegetables and fruits are very important food items that are widely consumed in Nigeria
and other countries of the world. They form an essential part of a balanced diet. Fruits and vegetables are
important sources of digestible carbohydrates, minerals and vitamins A and C. In addition, they provide
roughage (indigestible carbohydrates), which is needed for normal healthy digestion (Salunkhe and
Kadam, 1995).
Some methods of preservation of raw and processed fruits and vegetables include: storage in ventilated
shed, storage at low temperatures, use of evaporative coolant system, waxing and chemical treatment.
However, refrigeration is very popular but it has been observed that several Nigerian fruits and
vegetables, e.g. Banana, Plantain and Mango cannot be stored in the domestic refrigerator for a long
period of time as they are susceptible to chilling injury (NSPRI, 1990).
Consequently, in developing countries there is an interest in simple low-cost alternatives, many of which
depend on evaporative cooling which is simple and does not require any external power supply. Cooling
through the evaporation of water is an ancient and effective method of lowering temperature. Reduction
in the temperature of fruits and vegetables to retard spoilage is an important benefit of evaporative
cooling, though it is not the only one. Evaporation not only lowers the air temperature surrounding the
produce, it also increases the relative humidity. This helps prevents the drying out of produce and
therefore extends its shelf life.
35
Generally, an evaporative cooler is made of a porous material that is fed with water. Hot dry air is drawn
over the material. The water evaporates into the air raising its humidity and at the same time reducing the
temperature of the air.
Roy and Khardi (1985) described a fairly simple cooling system developed by the Indian Agricultural
Research Institute. The cooling chamber which has a capacity of about 100kg was built from bricks and
river sand, with a cover made from cane or other plant material and sacks or cloth. The structural details
included the floor which is built from a single layer of bricks, and then a cavity wall constructed of brick
around the outer edge of the floor and a gap of about 76.2mm between the inner wall and outer wall. This
cavity is then filled with sand. A covering for the chamber is made with canes covered in sacking all
mounted in a bamboo frame. The whole structure should be protected from the sun by making a roof to
provide shade. After construction, the walls, floor, sand in the cavity and cover are thoroughly saturated
with water. Once the chamber is completely wet, a twice-daily sprinkling of water is enough to maintain
the moisture and temperature of the chamber. A simple automated drip watering system can also be added
as shown in Figure 1.
Figure 1. A static cooling system (Source: Roy and Khardi (1985)).
According to Longmone (2003), Zeer which is an Arabic word for large pot was used in Sudan as
evaporative cooler to conserve food. He reported that the shelf life of the food products which included
tomatoes, Guava, rocket, okra and carrot increased substantially with the use of zeer. As a result of the
discovery, the Women’s Association for Earthenware Manufacturing started to produce and market the
pots specifically for food preservation. The description of the zeer is shown in Figure 2.
Figure 2. Pot-in-Pot (Source: Roy and Khardi (1985)).
36
The ripening of fruit and vegetables is caused by ethylene, a natural plant hormone. It initiates and
accelerates the ripening of fruit and vegetables, and then causes them to deteriorate. Ethylene reduces
storage life and quality, which also leads to increase in susceptibility of crops to physiological diseases
(Kader et al, 1995). The effects of ethylene are not all negative though; ethylene is beneficially used in
many instances such as the promotion of uniform ripening in banana, de-greening of fresh citrus, and as
an abscission agent for many crops. By lowering the level of ethylene surrounding fruits and vegetables,
their shelf life can be greatly increased, slowing the maturation of fruit, protecting vegetables, and greatly
reducing spoilage.
There are several ways that may be used to remove ethylene from produce storage areas. One of the
simplest and safest methods is to oxidize it with potassium permanganate. This reaction can remove
ethylene to very low levels. Potassium permanganate (KMnO4) is used in a number of familiar
applications, such as in drinking water treatment systems.
This research work is aimed at developing a metal-in-wall evaporative cooling storage for storing
perishable agricultural produce and to evaluate its performance with tomatoes and amaranthus.
2.1 Design Considerations for the Storage Structure
The following were considered in developing an evaporative cooling system for storing perishable
agricultural produce:
i. Availability of material for construction.
ii. Type of sand to be used as evaporating medium.
iii. The cost of the evaporative cooling system.
2.2 Design of the Cooling Chamber
The volume of the chamber is calculated from the equation;
(i) Volume of the chamber = length x breadth x height of the chamber
= 600mm x 600mm x 600mm = 0.216m3
The stored produce can occupy about 2 3 of the whole chamber.
Therefore, the chamber can store a maximum volume of 0.144m3 of produce at a time
(ii) Location of the loading/inspection door.
A hinge door is made through the edge of the metal box at one side for easy loading, inspection and
discharge of produce.
(iii) Arrangement of the tray inside the chamber.
The two trays shelves are arranged at 200mm apart in the cooling chamber. These trays allow easy
spreading of the produce stored on it to keep the produce from heaping.
2.3 Design of the Brick Wall
(i) Height of the Brick wall.
The wall was raised to a height of 600mm so as to be in the same level with the evaporative cooler.
(ii) Volume of the Brick wall.
The brick wall was constructed with a dimension of 1600mm x100mm x600mm high
Volume of the brick wall = length x breadth x height of the wall
=1600 x100 x 600 = 0.096m3
37
2.4 Design of the Area of the Cooling Medium (river-bed sand)
Area of the evaporative medium = area of the brick wall – area of the cooling chamber
Area of cooling chamber = 0.6m x 0.6m = 0.36m2
Area of the brick wall
= 1.1m x 1.6m = 1.76m2
Area of cooling medium = 1.76m2 – 0.36m2 = 1.40m2
2.5 Heat Load of the Evaporative Cooler
The evaporating medium is required to remove the heat load of the evaporative cooler for the storage of
fruits and vegetables through the cooled and humidified air emanating from it. The sources of heat loads
of the evaporative cooler were determined as follow:
(a) Heat gain by conduction, through the walls, roof and floor of the cooler was calculated using the
equation; Q =
(1)
Where: Q = heat transfer by conduction (W), K = 0.84wmk, A = total area of the various components, =
1.76 + 0.36 +1.4 = 3.52m2, dT = difference between outside and inside temperature (considering
maximum temperature) = (36-32)0C= 4°C, dt = insulation thickness (i.e distance between the cooling
chamber wall and the outer brick wall = 500mm or 0.5m)
Q = 0.84 x 3.52 x 4/5 = 23.65W
(b) Respiration Heat load of the Produce was calculated using the equation;
Qr = MP x Pr
2
Where: Qr = respiration heat (W/hr), MP = mass of produce, kg = 4kg (2kg each for both the tomatoes
and amaranthus), Pr = rate of respiration heat production = 0.0196W/kg hr (tomato), 0.02931W/kg hr
(amaranthus), Qr for the tomatoes= 2 x 0.0196 = 0.0392W/hr, Qr for the vegetable leaves = 2 x 0.02931=
0.0586 W/hr.
(c) Field Heat of the Produce was calculated using the equation of Rastasvoski, 1981;
Qf = (
)
3
Where: Qf = field heat picked up by produce (W), MP = mass of produce = 4kg (2kg each for both the
tomatoes and amaranthus), CP = specific heat capacity = 3.98 KJ/k °C (tomatoes), 3.7 KJ/k °C
(amaranthus), tc = cooling time (seconds) for fruits = 12hrs.
ΔT = change in temperature = 36-32= 4°C,
Qf for the tomatoes = 2 x 3.98 x 4 = 0.58W
12 x 60 x 60
Qf for the vegetables = 2 x 3.7 x 4 = 0.54W
12 x 60 x 60
(d) Infiltration of Air
The heat was estimated from 10 to 20% of the total heat load (Rastvoski, 1981, FAO/SIDA, 1986). Thus
taking an average of 15%, infiltration was calculated as;
QL = (Qc + Qf + Qr) x 15/100 = (Qc + Qf + Qr) x 0.15
(4)
Where: QL = heat transfer through cracks and opening of cooler door, Qc = 23.65W, Qf = 0.58W
(tomatoes) & 0.54W (amaranthus), Qr = 0.0392 W/hr (tomatoes) & 0.0586 W/hr (amaranthus).
Therefore,
QL for the tomatoes = (23.65 + 0.58 + 0.0392) x 0.15 = 3.64W
QL for the amaranthus = (23.65 + 0.54 + 0.0586) x 0.15 = 3.64W
38
2.6 Description of the Structure
The metal-in-wall evaporative cooling system consists of brick wall, a cooling chamber (metallic box) and
seabed sand which acts as the evaporating medium. The metallic box was installed into the brick wall while the
clearance between the metallic box and brick wall was filled with saturated sea bed sand. Therefore as
evaporation takes place through the seabed sand, there is a resultant cooling of the produce stored inside the
cooling chamber. The detailed description of the cooler is as shown in Figure 3.
Moist seabed sand
Metal-in-wall
Brick wall
Cooling chamber
Figure 3: Orthographic drawing of an evaporative cooling structure
The seabed sand was first saturated with water a day before loading the cooling chamber with produce.
About thirty litres of water was used daily to saturate the seabed sand and the brick wall while the daily
temperatures and relative humidity within and outside the chamber were measured and recorded in the
morning, afternoon and evening. Data collected were subjected to appropriate statistical analysis using
Excel software package.
2.7 Testing
The equipment was tested to determine the effectiveness of the chamber in terms of difference in
temperatures and relative humidity when compared with the ambient storage conditions. Also, tomatoes
and Amaranthus were stored separately inside the cooling chamber. The initial and final weights of the
stored products were measured for a period of eight days in both the evaporative cooler and ambient
storage. Visual inspection was carried out to determine deterioration level of the products during the
storage period.
The changes observed in the stored products are shown in table 1. It was observed that all the leafy
vegetable lost their tenderness within a day or two and the tomatoes became soft or pulpy in 3 to 4 days
under ambient conditions compared with the produce stored in the evaporative cooling chamber which
had high quality and firmness, although the leaves in the cooling structure retained its tenderness for the
period of eight days with little yellowish leaves.
39
Table 1. Changes in visual quality during storage
Tomatoes
Amaranthus
Days
(ecs)
Tomatoes (ambient)
(ecs)
1
4
4
4
2
4
2
4
3
4
1
4
4
4
4
5
4
4
6
3
4
7
3
4
8
2
4
Rating criteria for table 1 are
Leafy vegetables:
4: fresh & tender,
3: fairly tender,
2: wilted,
1: wilted & dry
Amaranthus
(ambient)
4
2
1
Fruits & other vegetables
4: hard,
3: firm,
2: fair firm,
1: pulpy & soft
The loss in weight of the fruits and amaranthus leaves in the evaporative cool chamber as well as in
ambient storage is presented in Table 2. It was observed that the weight loss was low in the evaporative
cool chamber while it was high in the ambient storage. The percentage weight loss in the cooler was 4%
and 17% for tomatoes and vegetable respectively while the percentage weight loss in ambient storage
condition was 24% and 74% for tomatoes and vegetable respectively as shown in Table 3.
Table 2. Weight loss of product in ambient storage condition and evaporative cooler
Initial weight
Weight after eight
days
Tomatoes
( EVC )
2000g
Tomatoes
(ambient)
2000g
Amaranthus
(EVC )
2000g
Amaranthus
(ambient)
2000g
1925g
1536g
1662g
528g
Table 3. Percentage weight loss of product in ambient storage condition and evaporative cooler
% weight loss
% weight loss ambient
Commodities
EVC
storage condition
Tomatoes
4
24
Amaranthus
17
74
Variations in temperature of the evaporative cooling chamber and ambient storage were recorded as
shown Figures 4, 5 and 6. The temperature inside the cooling chamber was significantly lower than the
ambient temperature. The cooling chamber had an average temperature drop of about 7° C when
compared the ambient temperature. As expected, the temperature inside the cooler was lowest in the
morning followed by evening temperature, while temperature during the afternoon was highest
throughout the period of study as shown in Figure 7. The average relative humidity inside the cool
chamber was found to be significantly higher than the outside ambient relative humidity as shown in
Figures 8, 9 and 10. A further analysis showed that an average relative humidity drop of about 4% was
experienced throughout the period of the study which is similar to the result of Odey et al (2005). Also as
expected, the relative humidity inside the cooler was highest in the morning period and lowest in the
afternoon throughout the period of the study as shown in Figure 11.
40
35
Temperature (0C
30
EVC temperature in the morning
25
Ambient temperature in the morning
20
15
10
5
0
0
2
4
6
8
10
No of Days
Temperature (0C)
Figure 4: Relationship between temperature inside the cooler and ambient
temperature in the morning
35
33
31
29
27
25
23
21
19
17
15
EVC temperature in the afternoon
Ambient temperature in the afternoon
0
2
4
6
8
10
No of Days
Figure 5: Relationship between temperature inside the cooler and ambient
temperature in the afternoon
41
35
30
EVC temperature in the evening
Temperature (0C)
25
Ambient temperature in the
evening
20
15
10
5
0
0
2
4
6
8
10
No of Days
Figure 6: Relationship between temperature inside the cooler and
ambient temperature in the evening
Temperature (0C)
27
EVC temperature in the morning
25
EVC temperature in the afternoon
23
EVC temperature in the evening
21
19
17
15
0
2
4
6
8
10
No of days
Fig.7: EVC temperature variations in the morning. afternoon and evening
42
88
Relative humidity (%)
86
84
Relative humidity inside EVC
in the morning
82
Ambient RH in the morning
80
78
76
74
72
0
2
4
6
8
10
No of Days
Fig. 8: Relationship between Relative humidity inside the EVC and ambient Relative
humidity in the morning
80
78
relative humidity inside
EVC in the afternoon
76
Ambient RH in the
afternoon
74
72
70
68
66
0
2
4
6
No of Days
8
10
Fig.9: Relationship between Relative humidity inside the EVC and
ambient in the afternoon
43
90
Ambient RH in the evening
85
80
relative humidity inside EVC in
the evening
75
70
65
60
55
50
0
2
4
6
8
10
No of Days
Fig.10 Relationship between the relative humidity inside the EVC and ambient in
the evening
90
85
Relative humidity inside EVC in
the morning
80
the afternoon
75
the evening
70
65
60
0
2
4
6
8
10
No of days
Fig. 11: EVC Relative humidity variations in the morning. afternoon
and evening
44
4. CONCLUSION
A metal-in-wall evaporative cooler has been designed, constructed and tested. Storage trials with
perishable agricultural produce were conducted for eight days without any noticeable deterioration. The
average temperature and relative humidity drop was about 70C and 4% respectively. Evaporative cooler
maintained the freshness of the perishable agricultural produce stored in it. Ripening process of the stored
produce was delayed thereby improving the storability of perishable agricultural produce in metal-in-wall
evaporative cooler. The metal-in-wall evaporative cooling system is efficient and can successfully store
fruits and vegetables for 6 to 8 days without any visible deterioration. The structure is subject to
modification to improve the storability of all perishable agricultural produce.
The storage structure is very economical since it requires no electrical or mechanical power to run. The
storage structure is therefore considered suitable for small scale farmers in the rural areas of Nigeria to
alleviate the problems of deterioration of their highly perishable crops and increase their financial
benefits.
REFERENCES
FAO/SIDA. 1986. Farm Structures in tropical climates, 6 FAO/SIDA, Rome.
Kader, S. T., Yamaguchi M, Pratt, H. K. and Morris L. L. 1995. Effects of storage temperature on
keeping quality and composition of onion bulbs on subsequent darkening of dehydrated flakes.
Proceedings of the American Society of Horticultural Science 69:421-6.
Longmone, A. P. 2003. Evaporative Cooling of Good Products by Vacuum. Food Trade Review.
(Pennwalt Ltd). 47.
NSPRI, 1990. Storage of fruits and vegetables. Nigerian Stored Product Research Institute Bull. 7.
Odey, K. O. Manuwa S. I. and Ogar, E. A. 2005. Sustenance of weight of vegetables during storage using
locally constructed evaporative cooler. Published proceedings of the 2nd annual conference of the
Nigerian Society of Indigenous Knowledge and Development, Obubra. Cross River State, Nigeria. pp
13-22.
Rastavorski, A. 1981. Heat balance in potato store centre for agricultural publication and documentation.
Wageningen, 210.
Roy, S. K. and Khardi, D. S. 1985. Zero Energy Cool Chamber. India Agricultural Research Institute:
New Delhi, India. Research Bulletin No.43: 23-30.
Salunkhe, D. K., and S. S. Kadam. 1995. Handbook of Fruit Science and Technology. New York:
Dekker.
45
MODELLING INCUBATION TEMPERATURE: THE EFFECTS OF INCUBATOR DESIGN,
EMBRYONIC DEVELOPMENT AND EGG SIZE
M. M. Jibrin1, F. I. Idike2, K. Ahmad3, U. Ibrahim4
Department of Electrical and Electronics Engineering, Sokoto State Polytechnic, Sokoto, Nigeria.
2
University of Nigeria, Nsukka, Enugu, Nigeria.
3
Department of Electrical and Computer Engineering, Ahmadu Bello University Zaria, Nigeria.
4
Department of Agricultural Economics and Rural Sociology, Ahmadu Bello University Zaria, Nigeria.
mmjibrin@yahoo.com, profidike@yahoo.com, kb_ahmed74@yahoo.com, lbrumar@yahoo.com.
1
ABSTRACT
This paper presents a modeling technique for optimum incubation temperature that would help immensely
in proper design of automatic electric incubators that would give better incubation results. The
fundamental theory of heat exchange is used to establish the nature of incubation temperature for eggs
embryo at the early incubation stage, intermediate incubation stage as well as at the advanced stage of the
incubation. The paper establishes the effect of the rate of air flow in the incubator on the temperature
distribution which affects the overall incubation efficiency of the incubator. However, it looks at the
relationship between the size of the eggs and the temperature requirement and distribution in the
incubator. The major achievement of the work is the fact that it gives the basis of selecting the operating
temperature of any incubator to be designed as well as setting the rate of air flow in the incubator for
uniform temperature distribution in the system. The paper also gives the basis of determining the
frequency of eggs tray turning in the incubator knowing the embryo development phases from beginning
to the end of the incubation stages. Therefore, this work is going to play a very fundamental role for
engineers that are involved in the design of automatic electric incubators since it establishes some
fundamental parameters that are very important for the incubators designers for best incubation
performance of the designed incubators.
KEYWORDS: Temperature, incubation, model, embryo metabolism, egg size.
1. INTRODUCTION
Most poultry species have an optimum incubation temperature of 37 OC to 38 OC and small deviations
from this optimum can have a major impact on hatching success and embryo development (Wilson,
1991). The vast majority of poultry hatching eggs are artificially incubated in incubators that must be
designed to accurately control the temperature inside the machine to ensure that the temperature of the
developing embryo does not deviate from this optimum.
The temperature experienced by the developing embryo is dependent on three factors: (1) the incubator
temperature, (2) the ability of heat to pass between the incubator and the embryo, and (3) the metabolic
heat production of the embryo itself.
The purpose of this review is to use a simple thermal energetic model of the artificial incubation process
to describe the interrelationships among the three factors that determine embryo temperature and discuss
some of the implications for the design of incubators.
2. THEORY OF HEAT EXCHANGE
The thermal energetic of incubation have been modeled by Kashkin (1961), Kendeigh (1963), Sotherland
et al. (1987), Turner (1991, 1994), and Meijerhof and van Beek (1994). A simple form of the model can
be given as
=
+
(
)
…………………… [1]
46
Where:
= temperature of the egg (OC);
= temperature of incubator (OC);
= heat
production of embryo at a given moment of incubation (J);
= heat loss from evaporative
cooling (J); and = thermal conductance of egg and surrounding boundary of air around the egg (J OC-1).
The heat balance of an animal is described by (Schmidt-Nielsen, 1975)
Or rewritten,
=
±
±
……………… [2]
−
=
+
……………… [3]
Where:
and
are the heat lost or gained by radiation and convection respectively (J). Equation
1 uses the terms
−
to describe the heat loss or gain from an egg because they are easier
to measure than either
or
. Heat transfer through radiation is assumed to be small because all
the surfaces within the machine will be at temperatures close to (within approximately 1 OC to 2 OC of)
the surface temperature of the egg. Kashkin (1961) estimated that 40% to 45% of the total heat loss from
a duck’s eggs was by radiation; however, this estimate has assumed that the total egg surface would be
able to radiate heat to the surface of the incubator. In a commercial incubator an egg would be surrounded
by other eggs at the same temperature, thereby reducing the effect radiation surface of the egg (Kashkin,
1961). It is therefore assumed that the main transfer of heat occurs through convection.
Equation 1 contains the term
because eggs continually lose water through incubation,
typically amounting to 12% of the fresh egg weight between the onset of incubation and the start of
piping (Ar, 1991). The phase change from liquid water to water vapor requires heat and at incubation
temperature this equates to approximately 580 cal/g of water lost (Schmidt- Nielsen, 1975). For example,
a 60 g chicken egg loses approximately 0.4 g of water/day, which equates to a heat loss of 232 cal/day or
11.2 mJ.
Embryo heat production can be measured directly, but Romijin and Lokhurst (1960) showed that it can be
estimated by measuring oxygen (O2) consumption. Every liter of O2 consumed by the embryo is
equivalent to the production of 4.69 kcal of heat (Vleck et al., 1980). Typical O2 consumption of a
chicken egg just before piping is 570 mL/day (Vleck and Vleck, 1987), equivalent to heat production of
2.67 kcal/day or 130 mJ.
At the onset of incubation,
is negligible and therefore Tegg < Tinc because
<
.
However, at the end of incubation,
>>
therefore Tegg > Tinc.. Fig. 1 shows
and
of chicken eggs measured by Romijin and Lokhorst (1960).
was observed to exceed
midway through the incubation period. Direct measurements of Tegg have also observed that it
exceeds Tinc midway through incubation in both chicken (Tazawa and Nakagawa, 1985) and turkeys
(Figure 2). The result is that during the first half of incubation, eggs will be gaining heat from the
surrounding air, whereas during the second half of incubation, eggs will lose heat.
The thermal conductivity term, K, used in Equation 1 combines the thermal conductivity of the egg (Kegg)
and the boundary layer of air around the egg (Kair). Sotherland et al. (1987) determined values for Kegg and
Kair and showed that the air boundary layer around the egg was approximately 100 ´ greater a barrier to
heat loss than the egg itself. These authors also showed that the value of Kair is dependent on the air speed
over the eggs and the relationship could be estimated as follows
47
= .
.
.
………………………………. [4]
Where: U = air speed (cms-1); and M = egg mass (g). The effect of changing air speed from 0 to 100 ms-1
or 400 ms-1 increased thermal conductance by approximately 2.5´ and 6´, respectively. A similar
relationship was found by Meijerhof and van Beek (1994).
An important consequence of the relationship between Kair and air speed is that the differential between
Tegg and Tinc during the second half of incubation will become greater at slower air speeds. Meijerhof and
van Beek (1994) estimated the increase in Tegg over Tinc for eggs of different weights and
at two air
speeds, 0.5.
48
Estimates based on the models of Sotherland et al. (1987) and Meijerhof and van Beek (1994), using a 50
g chicken egg with a metabolic heat output of 100 MJ. and 2 ms-1. Similarly, it is possible to use the
values of K derived by Sotherland et al. (1987) for air speeds of 0, 1, and 4 ms-1 in Equation 1 to estimate
Tegg – Tinc. Figure 3 plots the relationship between air speed and Tegg – Tinc derived from the two studies
based on a 50 g egg with a
of 100 mJ. As can be seen, there is good agreement between the
estimates of Tegg – Tinc between the two studies. The value of Kegg has been shown to increase during
incubation because the development of the network of blood vessels in the chorioallantoic membrane
underlying the shell improves heat flow (Tazawa et al., 1988).
The effect of blood flow on Kegg will increase as egg size increases but the overall effect on K will only
become significant if air resistance to heat transfer becomes small (Turner, 1987). In chicken eggs, blood
flow increased Kegg by approximately 20% (Tazawa et al., 1988). The thermal energetic model of artificial
incubation is relatively simple because heat is transferred between the egg and air totally surrounding the
egg. The situation is more complicated in natural incubation, in which heat is applied by the bird sitting
on the egg (Turner, 1991).
3. TEMPERATURES IN INCUBATORS
The use of thermal conductance, K, in Equation 1 has assumed a simple incubator that is an egg
surrounded by warm air. However, in commercial incubators the situation is much more complicated, as
each egg will be surrounded by many other eggs that may (in a single stage incubator) or may not (in a
multi-stage incubator) be at the same developmental stage. Although it is not the intention of this paper to
discuss the design requirements of an incubator, clearly the design of the incubator will have an effect on
the transfer of heat between the egg and the incubator air (Owen, 1991).
Incubators require an air conditioning unit to provide heat or cooling and humidification and a fan to
circulate the conditioned air through the eggs before being returned to the conditioning unit. The volume
of air that passes the eggs to transfer heat can be estimated using (Owen, 1991)
−
=
…………………………………. [5]
Where: (
−
) = the temperature rise in air flowing over the eggs (OC); F = factor, approximately
3.25 OC for incubator air at 37.5 OC and 50% RH;
= heat production of eggs in flow path (J); and
49
= flow rate of air over eggs (cm hr-1). The rise in air temperature as it passes over the eggs is
inversely proportional to air volume flow and therefore uniform control of egg temperature within the
incubator depends on uniform air movement around the eggs. As air flow has a negligible effect on water
loss from the eggs (Kaltofen, 1969; Spotila et al., 1981), there appears to be no limit to increasing air flow
to control temperature (Owen, 1991).
The uniformity of air flow within an incubator will depend on how easy it is for the air to pass between
the trays of eggs. This may be the path of greatest resistance to air movement and air may pass around the
mass of eggs, through spaces next to machine walls or between egg trolleys (Owen, 1991). Eggs must be
turned through 90° every hour for normal embryo development to take place (Tullett and Deeming, 1987)
and this is achieved in an incubator by tilting the egg trays at 45° from horizontal, the direction changing
every hour. In most incubators, turning is achieved by pivoting the individual trays around a fulcrum at
the center of the tray.
The effect of the turning is to reduce the space between the trays significantly from the spacing when the
trays are horizontal (Figure 4).
Using Equation 5, it is possible to estimate the effect of tray spacing on the air speed required over 18
days for chicken eggs to obtain an acceptable air temperature rise (0.5 OC). Assumptions made in the
calculations were: height of tray and eggs = 60 mm; tray dimensions = 0.9 m by 0.31 m, air assumed to
pass across the width of the egg tray; heat output per egg = 120 mJ; and tray capacity = 132 eggs, of
which 22 eggs are exposed to open air when tray is turned and therefore excluded from the calculation.
The relationship between tray spacing and required air speed to maintain egg temperature is shown in
Table 1. Two estimates are given, one assuming that both trays contain eggs at 18 days of incubation and
one assuming that one tray contains eggs that are less than midway through incubation and therefore
producing no heat.
As can be seen from Table 1, as the spacing between the trays increases, there is an exponential decline in
required air speed. Although actual spacing between trays in commercial incubators is highly variable,
with many of the newer machine designs incorporating greater tray spacing, it is not uncommon to see
trays that are sufficiently close together that large eggs on the tray are damaged by the tray above.
50
Table 1. The required air speed between egg trays in an incubator to maintain the same internal egg
temperature at different tray spacing
Distance between trays
Air Speed
0
Horizontal
Turned 45
One tray with 18
Both trays with 18
days eggs
days eggs
mm
m/s
30
3
4.8
9.6
35
7
2.1
4.1
40
11
1.3
2.6
50
18
0.8
1.6
60
25
0.6
1.2
There are little reported data on air speeds between trays in incubators, but values between 0.1 ms -1 and
3.0 ms-1 have been observed in chicken incubators (Kaltofen, 1969), less than 0.1 ms-1 in duck incubators
(Kashkin, 1961) and between 0.2 ms-1 and 2.2 ms-1 in a turkey incubator (French, unpublished
observations). The considerable variation in air speed between different locations within chicken and
turkey incubators would suggest that temperature variation would be observed in these machines.
Kaltofen (1969) investigated the relationship between air speed over the eggs, temperature of the air
surrounding the eggs and subsequent hatchability at different locations within a commercial incubator
(700 egg drum type, single stage and unspecified make). As part of the study, incubator fan speeds were
changed to give different air speeds over the eggs. Table 2 summarizes the main observations noted.
Increasing the incubator fan speed resulted in faster air speeds over the eggs and lower air temperatures,
supporting the predictions of Sotherland et al. (1987) and Meijerhof and van Beek (1994) that air speed
has a major influence on thermal conductivity. Air speed also varied between tray locations within the
machine, although only at the lowest fan speed did this result in a temperature difference between the
trays. The increase in temperature at the lowest fan speed was also sufficient to depress hatchability.
Mauldin and Buhr (1995) measured temperatures on top of eggs in a multi-stage chicken incubator and
observed that temperature was on the average, 1 OC warmer on the trays than at the temperature controller
of the incubator. Temperature on the trays also changed with time depending on the age of the eggs
within the incubator. Every 3 days or 4 days, 18 days old eggs were moved out of the incubator to be
transferred into a hatcher and they were replaced with fresh eggs. The initial effect of the movement of
eggs was to lower temperature just after the transfer. An increase of approximately 0.5 OC over the
following 3 days or 4 days was then observed, until temperature fell again at the next transfer. The study
illustrates the effect that the presence and management of other eggs within the incubator can have on the
temperature experienced by an individual egg.
The observation of Kaltofen (1969) and Mauldin and Buhr (1995) that temperatures recorded among the
eggs can differ markedly from the operating temperature of the incubator has also been observed in a
wide range of turkey incubators (Table 3). Maximum temperatures were recorded normally on eggs at the
end of incubation and were between 0.4 OC to 3.1 OC above the machine operation temperature. It is clear
from these studies that many commercial incubators are not able to maintain a uniform temperature
surrounding the incubating egg, principally due to uneven air flow within the machine. Improving
incubator design by improving air flows within the machines is an important goal for incubator
manufacturers. Techniques to directly measure K within incubators have been described by Meijerhof and
van Beek (1994).
51
Table 2. The effect of altering incubator fan speed, in rpm, on air speed over eggs, temperature among the
eggs, and hatchability at two locations within the incubator (Kaltofen, 1969)
Variable
Tray Position
Fan speed
Air speed (m/s)
Center bottom
60 (rpm)
120 (rpm)
180 (rpm)
O
Temperature( C)
Center bottom
Hatchability variance from
120 rpm treatment, % points
Center bottom
0.20
0.99
39.40
38.90
-23.20
-2.90
0.45
2.10
38.60
38.70
0.00
0.00
38.70
2.80
38.00
38.10
+0.40
-0.10
4. OPTIMUM INCUBATION TEMPERATURE
Optimum incubation temperature is normally defined as that required to achieve maximum hatchability.
However, Decuypere and Michels (1992) have argued that the quality of the hatchling should also be
considered. The effect of temperature on length of incubation has been observed in several studies
(Romanoff, 1935, 1936; Romanoff et al., 1938; Michels et al., 1974; French, 1994a) and on the rate of
embryo growth (Romanoff et al., 1938; Decuypere et al., 1979). Incubation temperature has been found to
affect the hatchling’s thermoregulatory ability, hormone levels, and post-hatching growth rate (Wilson,
1991; Decuypere, 1994). Ferguson (1994) has suggested something of potentially greater commercial
value to the effect that temperature may be able to alter the sex ratio by altering the phenotypic sex of a
proportion of chick embryo.
Studies investigating the effect of incubation temperature on the hatchability of poultry species have been
reviewed by Lundy (1969) and Wilson (1991). Several broad conclusions were drawn in these reviews:
1) Optimum continuous incubation temperature for poultry species is between 37 OC to 38 OC,
although hatchability is possible between 35 OC to 40.5 OC;
2) Embryos are more sensitive to high than to low temperature;
3) The effect of a suboptimal temperature will depend on both the degree of deviation from
optimum and the length of time applied;
4) Embryos appear to be more sensitive to suboptimal temperatures at the beginning of incubation that
at the end of incubation.
Recent studies suggest that optimum temperature may differ between poultry strains (Decuypere, 1994;
Christensen et al., 1994) or eggs of different sizes (French, 1994b). Interpretation of incubator
temperature studies is difficult because they use incubator operation temperature as the temperature
treatment applied to the egg. The data from both chicken and turkey incubators show that the temperature
indicated on the incubator control may be significantly different from the temperature of the air
surrounding the egg. The implication of Equation 1 is that the embryo inside the egg may be subjected to
a different temperature to the air surrounding the egg depending on the thermal conductivity of the
boundary layer of air around the egg. It is therefore possible that two studies using different incubation
systems can apply the same incubator temperature treatments but for widely different Temb results to be
observed.
The problem is illustrated by the elegant study of Ono et al. (1994). Chicken embryos between 12 days
and 20 days of incubation were subjected to a temperature of 48 OC and the time taken for the embryos’
hearts to stop beating was measured. As the embryos got older their tolerance time decreased from 100
min at 12 days to 56 min at 20 days. From this finding, it was concluded that older embryos are less
tolerant to high temperature. However, internal egg temperatures were also measured in this study and it
was found that, at all ages, embryos were dying when their internal egg temperature reached 46.5 OC.
Tolerance time became shorter with embryo age because older embryos had higher internal temperatures
at the start of the experiment.
52
Table 3. Temperatures recorded in turkey incubators in Europe and North America (French, unpublished
observations)
Temperature among eggs (OC)
Hatchery
Type of incubator
Operation
Mean
Maximum
Temperature
A
Drum multi-stage
37.5
37.9
38.7
B
Drum multi-stage
37.4
37.5
38.2
C
Tunnel multi-stage
37.0
37.2
37.8
D
Fixed rack multi-stage
37.6
37.8
38.0
E
37.4
37.4
38.0
F
37.4
37.4
38.2
G
37.5
37.6
38.2
H
Cabinet multi-stage
37.4
37.7
38.0
I
Cabinet single-stage
37.3
37.4
37.7
J
37.3
37.4
40.4
K
37.6
37.6
38.1
L
37.1
37.1
38.6
The important conclusion is that incubator temperature studies should measure the temperature
experienced by the embryo if the observations are to have wider relevance than to the particular incubator
used in the experiment. Most research work is undertaken in small incubators containing hundreds of
eggs, in which the difference between incubator temperature and that experienced by the embryo may not
be high. However, commercial incubators contain thousands of eggs and results from research may not be
transferable to the practical situation unless a common standard of egg temperature is used.
Measuring internal egg temperature is problematic because the structural integrity of the shell becomes
damaged, risking bacterial contamination and damage to the developing embryo. An alternative is to
measure shell surface temperature, as Kegg is high in comparison to Kair, resulting in only small differences
between internal and shell surface temperature (Sotherland et al., 1987; Figure 2). Unfortunately, the
author is unaware of any studies that have investigated the relationships between both internal or shell
temperature and subsequent hatching success, and this question would be an appropriate topic for
investigation.
5. TEMPERATURE AND EMBRYO METABOLISM
Studies on the effects of incubation temperature on embryo metabolism have been reviewed by Deeming
and Ferguson (1991). As temperature changes, so does the oxygen consumption of the embryo and,
hence, its heat production,
. Avian embryos for the majority of the incubation time are
poikilothermic and therefore do not increase their metabolic heat output to maintain Temb when Tinc
declines. Indeed, the opposite occurs and as Tinc decreases so does oxygen consumption. Tazawa et al.
(1989) showed that at about 18 days of incubation the chick embryo could maintain oxygen consumption
when temperature fell from 38 OC to 35 OC but as temperature decreased further, oxygen consumption
then declined. After piping, an increase in oxygen consumption in response to a decrease in Tinc has been
observed in both chickens (Tazawa et al., 1989) and Japanese quail (Nair et al., 1983), but full
thermoregulatory response in Galliformes only develops after hatching (Dietz and van Kampen, 1994).
Although metabolic responses to short-term changes in incubation temperature have been studied, only
limited data are available on responses to long term or continuous alterations to normal incubation
temperature. Chicken eggs incubated continuously at 38 OC or 35.5 OC had different growth rates but
oxygen consumption at comparable embryo mass was the same (Tazawa, 1973). Decuypere et al. (1979)
incubated chicken eggs at 35.8 OC, 36.8 OC, 37.8 OC, and 38.8 OC for the first 10 days and then at 37.6 OC
for the rest of incubation. Although the temperature treatments altered rate of development, embryo heat
production remained the same at equivalent developmental stages. Similar results were obtained with
turkey embryos incubated at 37.5 OC, 38.5 OC, 39.5 OC, and 40.5 OC for the first 6 days of incubation
53
(Meir and Ar, 1992, Tel-Aviv University, Tel-Aviv, 69978 Israel, personal communication). These
workers also investigated the effect on oxygen consumption by varying temperature either during the
second and last third of incubation or by using a lowering temperature regimen. Although temperature
changed growth rate, oxygen consumption per unit of dry embryo mass remained the same.
Contrary to the above observation, a study by Geers et al. (1983) showed that temperature could affect
oxygen consumption per unit of dry embryo mass. These workers incubated chicken eggs for the first 10
days at either 35.8 OC or 37.8 OC and then subsequently at 37.8 OC. Although the cool incubator
temperature reduced early embryo growth rate, once the cool embryos were returned to normal
temperature at 11 days they grew faster than the controls, confirming observations in an earlier study
(Geers et al., 1982) that embryos can exhibit compensatory growth. The faster growth in the cool treated
embryos resulted in a higher metabolic heat production per unit dry embryo mass than that of the control
group.
Hoyt (1987) developed a model that separated embryo metabolism between growth and maintenance and
used this model to predict that the pre-internal piping rate of oxygen consumption would be greater in
embryos that grow faster to achieve a given final embryo weight. The model would suggest that altering
embryo growth rate by manipulating incubation temperature would affect the rate of oxygen consumption
per gram of embryo mass; however, studies to critically test this prediction have not been undertaken and
the available evidence is ambiguous.
6. EGG SIZE
Equation 4 shows that thermal conductance
, scales with egg mass to the power of 0.53. The result is
that as egg mass increases, thermal conductance does not increase proportionally, so that larger eggs
should have greater difficulty losing metabolic heat produced by the embryo. Meijerhof and van Beek
(1993) predicted the rise in Temb over Tinc for eggs of different sizes for two hypotheses:
Hemb is 1) Constant per gram of egg,
2) Constant per egg regardless of size.
If Hemb per egg is constant, then Temb – Tinc should decline with egg size because of the increase in K.
Alternatively, if Hemb per gram is constant, Temb – Tinc increases with egg size because K does not
increase proportionally.
Table 4. Effect of fresh egg weight on the hatchability of turkey eggs incubated at three temperatures
(French, 1994b)
Incubator temperature (OC)
Fresh egg weight
70 to 79g
80 to 84g 85 to 89g 90 to 94g 95 to 104g
36.5
HOF,1
53.6a,x
73.5a,x
77.5a,x
77.4a,x
67.6a,x
%
28
102
147
93
37
n
69.7ab,x
78.9ab,x
80.6a,x
68.1ab,x
56.2b,x
37.5
HOF,1
33
109
139
91
32
%
n
54.8ab,x
48.3abc,y
47.0abc,y
34.7ac,y
25.0bc,y
38.5
HOF,1
31
118
134
95
32
%
n
1-Hatch of fertile eggs.
a-cHatchabilities within rows with no common superscript differ significantly (P < 0.05) using the G-Test
(Sokal and Rohlf, 1981).
xyHatchabilities within columns with no common superscript differ significantly (P < 0.05) using the GTest (Sokal and Rohlf, 1981).
54
The estimates of Meijerhof and van Beek (1994) are, of course, artificial, as Hemb does not remain
constant per egg nor per gram of egg regardless of egg size. Inter-specific allometric relationships
between egg mass (M) and the rate of oxygen consumption before internal piping (PIP VO2, milliliters
per day) have been investigated in several studies (Rahn et al., 1974; Hoyt et al., 1978; Vleck et al., 1980;
Vleck and Vleck, 1987), and the following relationship was derived:
log
2 = 1.36 + 0.73 log
…………....…. [6]
Poultry species do not deviate significantly from this relationship (Vleck, 1991). However, Hoyt (1980)
has observed that the above relationship does include an independent relationship between PIP VO2 and
the length of incubation, because larger eggs tend to have longer incubation times. PIP VO2 was related
to M and incubation period (I, days),
2 = 139
.
.
………………………….….. [7]
Using Equation 7 to estimate Hemb just before piping and Equation 4 to estimate K, Figure 5 shows the
predicted relationship between egg size and Temb –
for eggs with an incubation period of 28 days.
Although the temperature gradient does increase with egg mass, the rate of increase is low, with
temperature increasing by 0.1 OC over a 30 g egg mass range. Based on Figure 5, it is possible to predict
that eggs of different mass should not have significantly different incubation temperature requirements.
This prediction is not in accordance with the data presented in Table 4, taken from French (1994b). At
high incubation temperatures (38.5 OC), turkey hatchability progressively decreased with increasing egg
size and large eggs had the best hatchability when incubated at a reduced incubation temperature (36.5
O
C). The decline in hatchability at high temperature with increased egg size occurred mainly due to an
increase in embryo mortality between 24 days to 26 days of incubation (French, unpublished
observations), coinciding with the stage before internal piping. Other data presented in French (1994b)
showed that large eggs hatched better when incubation temperature was reduced from 37.5 OC to 36.5 OC
during the second half of incubation; however, similar improvements were not observed in small eggs. As
far as the author is aware, no other studies have investigated the possible relationship between egg size
and incubation temperature, and this relationship warrants further investigation.
The hypothesis that large eggs are more sensitive to high temperatures than small eggs is supported by
many studies that have shown large eggs do not hatch as well as small eggs (Landauer, 1961).
55
Fig. 5. The predicted relationship between egg size and the temperature gradient between the inside of the
egg (Tegg) and the incubator air (Tinc) just before internal piping. The prediction is based on an egg with a
28 days incubation period and has pre-internal piping oxygen consumption estimated using Equation 7 in
the text.
Table 5. Metabolic heat production of turkey embryos
Egg weight (g)
Pre internal piping metabolic heat
production (mJ)
79
1342
Reference
Rahn (1981)
88
1742
Dietz (1995)
88
1942
Tullett1
100
2172
Tullett1
1
Tullett (1983, AFRC Poultry Research Centre, Roslin, Midlothian EH25 9PS, UK, personal
communication)
2
Estimated from oxygen consumption
More recently, Ogunshile and Sparks (1995) have shown that broiler hatchability decreases with
increasing egg size when eggs are incubated at normal temperatures.
Figure 5 does not show a large increase in Temb – Tinc with increasing egg size because PIP VO2, and
therefore Hemb, only scale with egg mass to the power of 0.848 (Equation 7). The limited data available on
either PIP VO2 or Hemb of turkey eggs of different sizes are shown in Table 5 and plotted with the
estimate of Hemb derived from Equation 7 in Figure 6. It would appear that Hemb of turkey eggs increases
with egg mass at a greater rate than that predicted by Equation 7. Hoyt and Roberts (1985) showed that
the scaling of embryo mass and PIP VO2 differed between inter-specific comparisons and intra-specific
comparisons derived from five poultry species. However, it is unlikely that the disparity between
predicted and actual Hemb observed in Figure 5 can be accounted for by the use of intra-specific scaling of
PIP VO2, as the scaling component is still close to ã as used in Equations 6 and 7 (Hoyt, 1987).
Figue 6. Predicted and actual embryo metabolic heat production of turkey embryos as affected by egg
size. The predicted heat production derived from Equation 7 in text. Sources of actual heat production
data are given in Table 5.
56
Understanding the relationship between egg size and incubation temperature requirements has important
implications for the hatching industry and further investigation is needed. Monitoring internal or surface
temperatures of eggs of different sizes would be of interest to determine whether large eggs do have a
greater difficulty losing heat at the end of incubation. Problems may also arise in commercial incubators
that do not have sufficient heating, cooling, and air exchange capacity for a total egg mass larger than the
machine was originally designed. It is not uncommon to see a decrease in hatchability when the egg
capacity of an incubator is increased above its original specification or when an incubator is adapted from
chicken to turkey eggs without proper adjustment for the change in total egg mass within the machine.
Today, incubator manufacturers are moving towards designing incubators for individual poultry species,
which is a positive step for the whole industry.
7. CONCLUSIONS
The temperature experienced by the developing embryo is dependent on the incubator temperature, the
metabolic heat production of the embryo, and the thermal conductance of the egg and surrounding air.
Studies investigating the effects of temperature on the development and hatchability of poultry embryos
have concentrated mainly on the effects of incubator temperature and have ignored the other two factors.
Equation 1 provides a simple model that provides a more accurate description of egg temperature than can
be achieved by simply equating egg and incubator temperature. The model can also be used to predict the
effects of incubator design on egg temperature and highlights the importance of air flow within the
machine. Further studies are required to determine the effects of incubation temperature and egg mass on
the metabolic heat production of poultry embryos.
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Sotherland, P. R., J. R. Spotila, and C. V. Paganelli, 1987. Avian eggs: Barriers to the exchange of heat
and mass. J. Exp. Zool. Suppl. 1:81–86.
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bird eggs: Effects of wind speed and egg size. Physiol. Zool. 54: 195–202.
Tazawa, H., 1973. Hypothermal effect on the gas exchange in chicken embryo. Respir. Physiol. 17:21–31.
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chick embryo to hypothermal stress. J. Comp. Physiol. 155B: 195–200.
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UK.
59
MODIFICATION AND PERFORMANCE EVALUATION OF AFRICAN BUSH MANGO
(Irvingia gabomensis) CRACKER
E. A. Ajav1 and R. A. Busari2
Department of Agricultural and Environmental Engineering, Faculty of Technology,
University of Ibadan, Ibadan, Oyo State, Nigeria.
eaajav@skannet.com
2
Department of Food, Agricultural and Biological Engineering, College of Engineering and Technology,
Kwara State University Malete, Ilorin, Kwara State, Nigeria.
1
ABSTRACT
An African bush mango cracker was modified and fabricated to address the challenges of the
conventional method of cracking nuts which involves striking the nut. The tedious nature of this process
constitutes a major setback which restricts the process to a very small scale. The existing cracker was
designed for batch operation; the designed was complex, ineffective, expensive, low output capacity and
low efficiency. The modified machine was evaluated with respect to throughput capacity and cracking
efficiency at five moisture content levels (13%, 15% 17%, 20% and 25%) M.C. (dry basis). At 13% MC;
the output capacity was 7.13 kg/hr and cracking efficiency was 98% while at 25% MC as the output
capacity and cracking efficiency showed a reduction to 6.50 kg/hr and 90% respectively. Hence moisture
content is a dominant factor affecting the effectiveness of the machine. These results were different from
the old cracker that had throughput capacity and efficiency of 4.32 kg/hr and 70% respectively. The cost
of production of the machine was ₦52, 500 ($350). Based on these results, drudgery and other hazards
associated with manual cracking of the African bush mango were eliminated, the machine saves time and
made processing of the seeds easier.
KEYWORDS: Cracking machine, African bush mango, output capacity, cracking efficiency.
1. INTRODUCTION
Irvingia gabomensis is a non-timber forest product, made up of tree trunk (stem), leaves, roots and fruits.
The fruit comprises a fleshy part and the nut, which consist of a hard shell and the kernel/seed. Its seeds
have an outer brown testa (hull) and two white cotyledons. However, two species which are commonly
available is the Irvingia gabonesis which is found in Nigeria and Irvingia Wombolu which is found along
the coastal region of Senegal (Ladipo et. al., 1996). Irvingia gabonesis common names are bush mango,
African mango, wild mango or dika nut plant. This fruit is like that of a small, cultivated mango in
appearance, although they are unrelated. The pulp of this fruit is eaten fresh and the kernel of the nut is a
food additive. Cracking of Africa bush mango is a key operation in the processing of nut as it separates
the kernel from the dried nut. Traditionally, nuts are cracked manually by striking the nuts in-between
stone surfaces. The output and the tedious nature of this process form a major bottleneck, which restricts
the process to a very small scale. Furthermore, the manual process often constitutes a source of injury to
the operator that often gets hit by the stone used for cracking. Control of kernel damage is difficult and is
often based on the ingenuity of the operator. Separation of kernels from the shells is an arduous task,
which is made more difficult when the kernels are broken. As a result of this, the quality and quantity of
the product have remained low and therefore renders manual cracking ineffective. However, African
bush mango nut are irregular in shape and must be carefully positioned to break the nut along its natural
seam. The dried kernel-in-shell is brittle and a large percentage is crushed during the process, thereby
reducing the market value of the kernels. There is therefore need to develop system of extracting the
seeds by developing a mechanical cracker which could drastically reduce drudgery and increase both
production and market value.
Asoegwu and Maduire (1996) investigated some physical properties and the cracking energy of Irvingina
Gabonensis (Ogbono) nuts. The average sphericity was 53.3%, roundness 73.5% and density of
60
1.35g/cm3 at 44.8% moisture content (db). An impinging velocity of 69.54m/s was adequate to
sufficiently crack the seed at the determined moisture content while the energy required for the cracking
varied from 17.31 J to 27.52 J.
Oluwole et. al., (2004) designed, constructed and evaluated the performance of sheanut-cracker. The
authors reported that the moisture content affected the cracking, breakage and winnowing efficiency.
Feed rate also had effect on the performance evaluation of the machine. Three different vane
configurations were employed in carrying out the evaluation and it was observed that the radial vane
configuration maintained the best cracking performance. Ogunsina et. al., (2008) designed constructed
and evaluated the performance of a table mounted device for cracking dika nut. It was reported that the
failure of nut was along the line of symmetry and the machine gave 100% cracking efficiency with 24%
breakage in cracking sun dried dika nut at 6.6% moisture content (w.b). Diabana, (2009) designed,
constructed and evaluated the performance of an African bush Mango (irvingia gabonesis) cracker. He
reported that the performance test showed that the moisture content did not affect crackability of the seed.
At a moisture content of 8% (db), the machine gave output capacity of 6.32 kg/hr and 96% cracking
efficiency while at 21% (db), the machine gave output capacity 4.32 kg/hr and 94% cracking efficiency
respectively.
Generally, nutcrackers (for palm nuts, cashew nut, bambara, groundnuts, shea butter nut etc.) which are
adequate for most nuts are not appropriate for bush mango because it was found that the nut shell has an
appreciable thickness. The shape was elliptical and ductile than other nut. It was also observed that the
nut crack best along its natural line of cleavage, which is the main reason why it is impossible to adopt
other nut crackers.
The purpose of this study was to modify and evaluate an African Bushh Mango Cracker.
2.1 Design Considerations
The following factors were considered in modifying African bush mango cracker; reduction in time and
energy spent in cracking, use locally available materials for constructing the cracker, detachable
components, using bolts to attach, for easy repair and maintenance, continuous operation, incorporation
of hopper for easy feeding of the nut into the cracking nut.
2.2 Existing African Bush Mango Cracker
The first attempt in the design of African bush mango cracker was carried out by Diabana, (2009). The
machine operated on the principle of reciprocating motion of piston and crankshaft of an engine and it
was designed for batch operation. The main components of the machine included connecting rod, cylinder
bore and a piston, shaft, cracking tray, and frame. Figure 1 shows the existing machine.
61
Figure 1: The Existing African Bush Mango Cracker
The following modifications were therefore made on the existing African bush mango cracker;
(i)
Incorporation of hopper and slanted feeding chute for easy loading of the nut into the cracker.
(ii) Discharge chute was provided to enhance quick discharge of the seeds into a collector.
(iii) Newly fabricated cracker was designed for continuous cracking.
(iv) The new machine was simple, light in weight and smaller in size compared with the old machine in
term of portability.
(v) The cost of production was lower and affordable by local processor compared with old design
(₦52,500.00 compare to ₦138,750.00 which was the cost of the old machine).
(vi) The output capacity and efficiency of the new design was higher than old cracker (output was 6.88
kg/hr and efficiency was 96%).
2.3 Power Requirements
The seed of the African bush mango is placed edgewise in between the fixed block and the slider
hammer, the seed is stationery to absorb the impact while the hammer is attached to the slider-crank
mechanism, moving in reciprocating form. However, there is energy translation in the process that is
kinetic energy in the hammer is absorbed by the seed which posses potential energy as a result of its
position.
It therefore implies that the kinetic energy in the machine is equal to the potential energy absorbed by the
seed.
From equation of kinetic energy
K.E 
1
mv 2
2
(1)
Where;
K.E=Kinetic Energy, J, M= Mass of hammer, kg, V= Speed of the hammer, m/s,
From equation of Potential Energy
P.E  Mgh
(2)
62
Where;
P.E =Potential Energy, J
M= Mass of the seed, kg
g= Acceleration due to gravity, m/s
h= Distance travelled by the slider, m
But from principles base on the assumption of energy loss by the machine through hammer which is equal
to the energy absorbed by the seed to crack.
P.E=K.E
(3)
Mgh  1 mv 2
2
(3a)
Assuming the weight of the hammer is equal to the weight required to crack the seed, and making v the
subject of the formula, equation (3) becomes
v  2 gh
(4)
2.4 The Slider Crank Mechanism
l
r
θ
0
x
r+l
Fig 2. The slider crank mechanism
As the crank connecting the shaft rotates, it moves the slider in linear motion (Fig 2). The distance
travelled by the slider is therefore determined using the formula as stated in Singh (2005).
X
r[(1  cos  )  r (1  cos 2 )]
4l
(5)
Where;
r=Radius of crank, m
l=Length of connecting rod, m
0
θ=Angle between the crank radius and horizontal, θ
For the design, it is assumed that the crank radius is 150 mm.
Length of connecting rod from Singh (2005) is given as
n l
(6)
r
Where;
n= constant and value varies between 3.5 to 4 ( for internal combustion engines since the
mechanism is not an enclosure, maximum value will be considered).
Therefore n is considered to be 4 substituting into equation (6)
4 l
0.15
63
l  4 * 0.15  0.6  600mm
  45o
i e crank angle is assumed to be 45
Therefore;
0.15[(1  cos 45 0 )  0.15(1  cos 90 0 )]
X 
4  0 .6
0.044  0.15
X 
2 .4
X  0.08m  80mm
Substituting the value of X as h in equation (4), therefore v is obtained as;
V=1.25m/s
The speed of the hammer=1.25m/s
The velocity at which the slider travel can be equated to the angular speed and its radius
(Khurmi and Gupta, 2004).
V  Wr
(7)
Where;
V=Speed of the hammer, m/s
W=Angular velocity, rad/s
r=Length of connecting rod, m
w v
r
(8)
V=1.25m/s, r=0.6
w  1.25
0 .6
=2.1rad/sec
As earlier stated by Singh (2005),
W  2N
60
Where;
W=Angular velocity, rad/sec
N=Number of revolution per minute
N  W  60
2
 2.1  60
2
=20rev/min
(9)
Service factor Ks is considered to take care of losses due to transmission. The value Ks was obtained
from standard table which is in appendix table B2.
=20×1.54
=30.8rpm
For the purpose of these design 50 revolutions per minutes is considered.
2.5 Power Developed
The power developed by the hammer as a result of the rotation is calculated using the formula given by
Singh (2005),
64
P  TN
9550
Where;
P=Power developed, kw
T=Torque, N m
N=Speed of the machine, rpm
But,
T  JG
L
(10)
(11)
Where;
J=Polar moment, mm4
G=Modulus of rigidity, N/mm2
θ=Angle of twist, deg.
L=Length of shaft or connecting rod, m
Polar moment of a solid shaft is given by Singh (2005).
J  d
4
(12)
32
Where;
d    30
4
32
=79,521.56mm4
G=80,000N/mm2
 
180
Substituting the above values into equation (11)
80,000  79,521.56  
180  600
T  185, 055.07 N . mm

Substituting the obtained torque into equation (10)
TN
9550
185,055.07  50

9550
P
=968.87w
=0.97kw
Converting the power obtained to horsepower which is the commonly used rating for electric motor,
1Hp  746w
968.87
 1.3Hp
746
For design purpose, service factor must be considered in other to consider losses in the machine during
operation. To obtain the service factor, values were obtained from standard table which is appendix table
B2.
Therefore to calculate for the maximum power Singh (2005) stated the formula as
KS 
Maximum Rated Power ( PM )
Actual Power Re quirement ( PA )
(13)
65
Where;
The actual power requirement is the power calculated which is required to drive the slider
KS 
PM
1.3
(13a)
Form medium shock, worm gear operation and frictional losses for 8hours per day.
k  1.54
p  1.5  1.54
s
m
 2.002 Hp
 2 Hp
The maximum power required is estimated to be 2 Hp (1.5Kw) and a speed of 50 revolutions per minute.
To achieve this speed, an electric motor with a reduction gear is attached to reduce the speed from
1440rpm to 50rpm.
2.6 Description of African Bush Mango Cracker
The cracker consist of the following basic units; frame, hopper, cracking unit, slider hammer, slot, feeding
chute, electric motor and reduction gear. The Figure 3 shows the entire component, the side view, front
view and plan elevation of the machine.
1
1.
2.
3.
4
Hopper
Feeding Chute
Slider Hammer
Slider-crank
Mechanism
5 Frame
6. Fixed Block
7. Cracking Table
8. Electric Motor
2 6
3
7
8
4
5
Gear Electric Motor
Fig 3. The African bush mango cracker
66
Fig 4. Plan elevation of the machine
The frame carried the entire component of the machine. It is a rectangular shaped structure,
(1050×749×756) mm. This is to provide stability and to withstand vibration, its pyramid shape; the inlet
dimension is 70mm by 70mm while the upper part is 200mm by 200mm and the height of hopper is
350mm. The seeds to be cracked are fed into cracking unit by gravity through feeding chute from the
hopper. The cracking unit comprises of fixed block and slider hammer and the unit carried out the
function of actually cracking the seeds, released nuts and cracked shells will fall into collector through
slot provided.
2.7 Mode of Operation
The cracking machine is designed for continuous operation. To achieve this operation, a hopper with
slanting feeding chute is incorporated into the machine. The seed flows by gravity from the hopper to the
cracking unit. The nut is compressed between the slider and fixed block until it gives a sound that
connotes cracking. The cracked seed fall to the ground or into a container through slot provided which
gives room for another seed to come in and the process continue.
2.8 Machine Evaluation
Performance evaluation was carried out on the cracker to determine the effect of moisture content on
output capacity, cracking efficiency and percentage breakage.
One hundred nuts were selected for conditioning from equilibrium moisture content of 17% to 13%, 15%,
20%, and 25% (dry basis) by moisture adjustment. But the seeds were first dry to bone dry weight before
67
the addition of water. The amount of water to be added for each batch of sample was determined from the
following relation (Adebona, et.al., 1986).
 M  M1 

WW  WS  2
 1 M 2 
(14)
Where;
WW = amount of water to be added, g
WS = weight of sample for which moisture is to be adjusted, g
M 1 = initial moisture content of sample, %
M 2 = final moisture content of sample. %
The conditioned samples were weighed before being fed into the cracker. The time spent to crack the
weighed sample was taken and recorded. After cracking operation, the cracked wholesome seeds, split
seeds, broken nuts and uncracked seeds were collected, separated and weighed individually. The
following were used for analysis of the results and there were five replications.
Output Capacity (OC) =
WC
t
(15)
Where; WC= weight of cracked seeds, kg, t = time taken, hr.
Cracking Efficiency (CE) =
NC
 100
NT
(16)
Where; Nc = Number of cracked kernels, NT = Total number of nuts.
Percentage Breakage (PB) =
Nb
 100
NT
(17)
Where; Nb = Number of broken or partially damaged nuts, NT = Total number of seeds.
The statistical analysis was carried out using ANOVA to test for the significant differences in the output
capacity at five different moisture contents. The results of the statistical analysis are presented in Table 2.
The modified machine was tested. The results of the performance evaluation are presented in Table 1.
Table 1. The Results of the performance evaluation of the machine
Parameters
M C 13% db
M C 15% db
M C 17% db
Weight (kg)
1.061
1.274
1.382
M C 20% db
1.435
M C 25% db
1.565
Time (hrs)
0.150
0.182
0.197
0.213
0.241
Throughput
(kg/hr)
Wholesome
seeds
Split seeds
Broken seeds
Uncracked
seeds
Efficiency (%)
7.13
7.04
7.02
6.74
6.50
6
8
12
13
15
88
4
2
85
3
4
81
2
5
79
1
7
75
0
10
98
96
95
93
90
The effect of moisture contents on the output capacity and cracking efficiency is shown in Table 1. The
lower the moisture content, the higher the output capacity and the efficiency. Therefore, to have a high
68
efficiency, the moisture content must be low. At 13% MC; 4% of the seed cracked were broken and 2%
of the seeds were not cracked, the output capacity was 7.13 kg/hr and cracking efficiency was 98% while
at 15% MC; 3% of the seed cracked were broken and 4% of the seeds were not cracked, the output
capacity and cracking efficiency reduced to 7.04 kg/hr and 96% respectively. Similarly, at 17% MC; 2%
of the seeds cracked were broken and 5% of the seeds were not cracked, output capacity and cracking
efficiency further reduced to 7.02 kg/hr and 95% respectively while at 20% MC; 1% of the seeds cracked
were broken and 7% of the seeds were not cracked, the output capacity and cracking efficiency came
down to 6.74 kg/hr and 93%. There was a similar trend when the test was performed at 25% MC as the
output capacity and cracking efficiency showed a further reduction to 6.50 kg/hr and 90% respectively,
there were no broken seed and 10% of the seeds were not cracked. These results show that moisture
content is a dominant factor affecting the effectiveness of the machine and that the modified machine is
better in term of throughput capacity and efficiency compared with the old cracker that gave throughput
and efficiency of 4.32 kg/hr and 70% respectively.
Table 2: Analysis of variance for output capacity of the machine at five different moisture contents
Variation
Between
Treatment
Within
Treatment
Total
Degree of
Freedom
4
Sum of
Square
1.36
Square Mean
Fcal
Ftabs
0.3400
4.4
2.87
20
1.53
0.0765
24
2.89
This Table shows that there are significant differences in output capacity for different moisture content at
5% level of significance. Hence moisture content is a dominant factor affecting the effectiveness of the
machine.
The material used and their cost as at the time of fabrication of the African bush mango cracker is
presented in Table 2. The cost of production was determined by multiplying the unit cost of each material
used by the quantity required. The total sum of all the material cost was taken as cost of production. On
the whole the cost of the machine was ₦52,500 ($350). The most expensive materials used were the
square pipe which costs ₦14,000, electric motor which also costs ₦10,000 and the cheapest material used
was rod (20mm) which costs ₦400 only.
Table 3. Cost analysis of construction of Africa bush mango cracking machine
Materials
Quantity
Unit cost (N)
Cost (₦)
Square pipe (4 by 4cm)
2
7000
14,000
Square pipe (2.5 by
½
3,500
2.5cm)
Mild-steel plate (1.5mm)
½
2,000
Electrode
1pkt
1,500
Electric motor
1
10,000
Bearing (pillow)
2
750
1,500
Bolts and Nut
20
40
800
Rod (30mm)
½ length
800
Rod (20mm)
¼ length
400
Flywheel
1
1,000
Painting
2,000
Workmanship
15,000
Total
52,500 ($350)
69
4. CONCLUSIONS AND RECOMMENDATIONS
The modified machine is simple in design, low cost, safe and easy to operate. The principle of operation
is by compressing the nut between two solid blocks. At the end, 95% average cracking efficiency was
achieved and 2% breakages were obtained while output capacity ranges from 7.13 kg/hr to 6.50 kg/hr for
13% M C and 25% M C respectively. Based on these results, drudgery and other hazards associated with
manual cracking of the seed are eliminated, the machine saves time and made processing of the seeds
easier. The machine could be further improved by incorporating a mechanism to separate shells from the
kernels.
REFERENCES
Adebona, M. B., Ogunsua, A. O., Babalola, C. O. and Ologunde, M. O. 1986. The Handling, Processing
and Preservation of Tetracaspidium. Proceedings of the First National Symposium on Food
Processing of the Nigerian Society of Food Science and Technology, held at Obafemi Awolowo
University Conference Centre, Ile-Ife, Nigeria Pp 15-17.
Asoegwu S. N. and J. O. Maduire, 1996. Some Physical Properties and Cracking Energy of Irvingia
Gabonensis. Journal of Nigerian Institute of Agricultural Engineers. Pp 130-139.
Diabana, P. D. 2009: Design, Construction and Performance Evaluation of an African Bush Mango
(Irvingia Gabonesis) Cracking Machine. Unpublished M.Sc Project Submitted to the Department of
Agricultural and Environment Engineering, University of Ibadan
Khurmi R. S. and J. K. Gupta, 2004. Machine Design. Eurasia Publishing House (Pvt) Ltd, Ram Nagar
New Delhi.
Ladipo D. O., J. M. Fondown, N. Ganga, R. R. B Leakey, A. B Temu, M. Melnyk and P. Vantomme
1996. Domestication of the Bush Mango (Irvingia spp): Some Exploitable Intra-specific Variations in
West and Central Africa. In Domestication and Commercialization of Non-timber Forest Products in
Agro Foresting Systems. Proceedings of an International Conference Held in Nairobi Kenya, 19-23.
February Non wood Forest Products vol. 9: Pp 193-205.
Ogunsina B. S., O. A. Koya, and O. O. Adeosun. 2008. A Table Mounted Device for Cracking Dika
Nut. Journal of Agricultural Engineering International: The CIGR E-Journal Manuscript PM 08011
vol.1 August, 2008.
Oluwole F. A., N. A. Aviara and M. A. Haque, 2004. Development and Performance Test of a Sheanut
Cracker. Journal of Food Engineering vole (65) pg 117-123.
Singh S. 2005. Machine Design Khanna Publishers Delhi Pp 557-704.
APPENDIX
Table: B2 Values of services factor (Ks)
Type of Service
Service Factor (Ks) for
Radial Ball Bearings
Uniform and steady load
1.0
Light shock load
1.5
Moderate shock load
2.0
Heavy shock load
2.5
Extreme shock load
3.0
(Khurmi and Gupta 2004)
70
DEVELOPMENT OF A DIGITAL DENSITOMETER
S. L. Ezeoha1, C. C. Mbajiorgu1, and V. U. Obi2
Department of Agricultural and Bioresources Engineering,
University of Nigeria, Nsukka, Nigeria.
louiezeoha@yahoo.com
2
Century-21 Design Group, University of Nigeria, Nsukka, Nigeria.
1
ABSTRACT
A digital densitometer was designed and a prototype constructed. The design of the displacer was based
on Archimedes principle of floatation, while the design of the digital component was based on the
principle of optical-sensing and signal transformation. The prototype model was used to measure the
densities of water, palm kernel oil, paraffin oil, and glycerin at a laboratory-room temperature of 33oC.
The tests results were 0.99g/cm3, 0.99g/cm3, 0.99g/cm3, and 1.05g/cm3 for water, palm kernel oil, paraffin
oil, and glycerin respectively, showing a maximum error of +13.9% when compared with the actual
densities of the liquids (0.96, 0.88, 0.87, and 1.06g/cm3 respectively). The readings of this first version of
the densitometer are obtained indirectly. Work is in progress to develop a model that can give direct
digital readings.
KEYWORDS: Density, densitometer, instrumentation, digital, hydrometer.
1. INTRODUCTION
According to Turner (1988) the science of instrumentation is of fundamental importance to engineers,
scientists, and medical workers. Instruments are the eyes and ears of the scientists, technologists, and
engineers. By measuring the density of a process stream, one can determine its’ concentration,
composition, or in case of fuels, its calorific value. Density measurement is also necessary to convert
volumetric flow measurement into mass flow information (Hoeppner and Liptak 1995a). Density is
defined as the quantity of matter per unit volume. The most common unit is grams per cubic centimeter.
Other units include API degrees (o API) for petroleum products, Balling degrees (o Ba) for brewing and
sugar industries, Barkometer degrees (o Bk) for tanning industries, Baume degrees (o Be) for acids and
syrups, the unit of Proof also for the alcohol industries, the Twaddell degrees (o Tw) also for the sugar,
tanning, and acid industries, the Brix degrees (o Br) also for sugar industries, the Quevenne degrees (o Q)
for dairy industries, the Sikes, Richter, or Tralles degrees (o S, o R, o T) for alcohol industries (Hoeppner
and Liptak, 1995a).
Relative density or specific gravity is as the ratio between the density of a process material to that of
water or air at specified conditions. Being a ratio, this property is unit-less. For liquids, specific gravity,
SG = 1 corresponds to 1g/cm3. Both density and specific gravity characterize the same physical property
of the process media, and they are meaningful only if defined at stated temperature level (Hoeppner and
Liptak, 1995a). Liquids’ densities are measured in terms of their density or in terms of their specific
gravity or relative density, which is the ratio of the density of the measured substance to the density of
water. The compressibility of most liquids is slight and the effects of pressure upon density measurement
generally may be disregarded. When a selection of liquid density gauges is to be made, several
considerations often influence the decision. If a transmitter is needed, the most economical selections are
the hydraulic head and the displacement type sensors. But if only local indication is required, then the
hydrometer represents the least expensive choice. Most density gauges can only be used on clean, nonviscous fluids. The selection for these applications can be based on economics and accuracy. If the
process fluid is viscous or of the slurry type, then the radiation, coriolis, ultrasonic, vibrating, hydrostatic
head, and U- or straight-tube sensors can be considered (Hoeppner and Liptak, 1995a).
71
The hydrometer element consists of a weighted displacer with a small-diameter indicator stem attachment
at the top. The stem is graduated in any of the density units. According to Archimedes principle, when a
body is immersed in a fluid it loses weight equal to the weight of the fluid displaced. The hydrometer
element is a constant – weight body that if immersed in fluids with differing densities will displace
differing volumes of fluids. Therefore, the degree of stem scale submersion is an indication of the process
fluid’s density. Readings are made at the point where the stem emerges from the liquid. The hydrometer
stem position could be read manually, detected optically, or transmitted electronically using either the
servo-operated impedance bridge or the capacitance bridge.
The accuracy of measurement is a function of surface tension, turbulence, and sample contamination, all
of which affect reading accuracy. Hydrometers are accurate, frictionless, and direct–indicating without
need for mechanical linkages or external energy sources; and are compatible with most corrosive fluids.
Their limitations are in the process fluid they can handle and in the pressures and temperatures they can
be exposed to. Because the float position should not be affected by anything except the fluid density, the
velocity, friction, turbulence, and viscosity effects must be minimized. Also, because the basis for their
operation is the constant float, material build–up on the float cannot be tolerated (Hoeppner and Liptak,
1995b). The criterion for selecting any material for the float or displacer is lightweight. Based on this, the
best choice often includes Aluminum metal and Glass with a density of 2.6g/cm3 and 2.7g/cm3
respectively, compared to Copper and Steel with densities of 6.3g/cm3 and 7.7g/cm3 respectively. On the
other hand, the criteria for selecting any material for the liquid container are size, and stability. A
displacer or float made of a hollow cylinder with sealed bottom will be less dense than a solid cylinder of
same diameter. And any displacer for measuring the density of any liquid should be less dense than the
liquid.
In food and bioprocess engineering, a lot of liquid products are encountered. They include water,
vegetable oils, bio fuels, etc. Density can be used as an index of quality for these liquid products by
comparing specimen values with standard values for clean, unadulterated, or normal concentration
products. Incidentally, instruments that measure liquid density are not common sights in Nigeria, even in
scientific equipment stores. What are available in most laboratories and scientific equipment stores are the
acid hydrometers often used by electricians for the management of lead-acid batteries. The need therefore
exist for a simple, cheap, versatile, laboratory instrument for measuring the density of liquid products.
The objectives of this study were to show graphically the variation of float displacement in liquids with
the density of the liquids and to develop a digital densitometer that could be used to measure and indicate
the density of liquids, especially vegetable oils and liquid bio-fuels.
2.
MATERIALS AND METHODS
The simplest instrument for the measurement of liquid density is the hydrometer. A hydrometer consists
of two major parts namely, the displacer or float and the liquid container.
The design objective was to produce a densitometer that could be used to measure and indicate liquid
densities from 0.45g/cm3 -1.63g/cm3.
Procedure:
i. Known: Diameter of available Aluminum. Pipes, Dd = 2.618cm
ii. Assumptions: (a) Let the density of the displacer, ρd = 0.44 g/cm3. (b) Let the mass of the
displacer, Md = 47.287g/cm3
iii. Calculations: (a) The volume of the displacer, Vd is given as:
Vd =
M d 47.287

 107.47cm3
d
0.44
72
(b) The length of the displacer, Ld, is calculated from the following expression: Vd = Ad Ld
Dd Ld
=
4
2

Ld =
4Vd
4x107.47 429.88


 20cm
2
2
Dd 3.14x2.618 21532
200mm
200mm
iv. Thus, a length of 20cm from the 2.618cm – diameter, cylindrical aluminum pipe was cut and
bottom – weighted and sealed with Lead (Pb) metal to produce a float weighing 47.287g (see Fig.
1).
40mm
26mm
Fig. 1: The densitometer displacer or float
Fig. 2: The densitometer liquid container
v. Also, 20cm length of a 4cm – diameter mild steel pipe was cut and bottom – sealed to produce
the liquid container (see Fig. 2).
vi. And then, using a fixed liquid volume of 150ml, a calibration table for the Aluminum- metal (Am) densitometer was generated (Table 1).
Table 1: Calibration Table for the A-m Densitometer
X
ρx
Md
Ad
Vxd
Ldx
A
1.632
47.287 5.383 28.975
5.383
B
1.262
37.470
6.961
C
0.998
47.382
8.802
Rx
8.860
7.958
6.906
Rx1
8.8
7.9
6.9
D
E
F
0.990
0.900
0.879
49.776
52.541
53.796
9.247
9.761
9.994
6.651
6.357
6.224
6.6
6.3
6.2
G
H
0.850
0.800
55.632
59.109
10.335
10.981
6.029
5.660
6.0
5.6
I
J
K
0.789
0.750
0.700
59.933
63.049
67.553
11.134
11.713
12.549
5.572
5.241
4.764
5.5
5.2
4.7
L
M
0.650
0.600
72.749
78.812
13.515
14.641
4.211
3.568
4.2
3.5
73
Where:
X = Name of the liquid
ρx = Density of the liquid (g/cm3)
Md = Mass of the displacer or float (g)
Ad = Cross-sectional area of the displacer (cm2)
Vxd = Volume of liquid, x, displaced (cm3)
Ldx = Length of displacer immersed in the liquid, X (cm)
Rx = Densitometer height reading for liquid X, to 3 decimal places (cm)
Rx1 = Densitometer reading for liquid X to 1 decimal place (cm)
Vxd =
Md
V
4V xd
, Ldx  xd 
x
Ad Dd 2
D d
Ad =
4
2
 4Vxd
Rx = Ld – Ldx – (Lc – 
 Dc
2

4VFx 
 ) (cm)
2
Dc 
Where: Ld = Length of displacer or float (cm)
Lc = Length of liquid container (cm)
VFx = Volume of liquid x in the container (ml or cm3)
Dc = Diameter of container (cm)
Dd = diameter of displacer (cm)
vii. Furthermore, a calibration curve was produced by plotting ρ x against the corresponding Rx (Fig.
3).
To convert the densitometer height readings (Rx) into digital readings (Dx), optical sensors were used. The
block diagram of the digital circuit is as shown in Fig. 4. The circuit consisted of optical sensors: the
infrared light transmitter (IR-TX), and receiver (IR-RX); 555-astable timer (oscillator) supported by a
monostable timer; an amplifier for impedance matching; binary counters (74192 I-Cs); 7-segment binary
decoders (7447 I-Cs); and 7-segment displays.
The digital circuit diagram is as shown in Fig. 5. The circuit is powered by a 9V DC source, via a pressbutton switch and a 5V voltage regulator. When the circuit is completed by this switch, the IR-RX
receives light from the IR-TX. But the amount or intensity of the infrared light received varies directly
with the distance between the fixed transmitter and the receiver whose position depends on the density of
liquid under investigation. The electrical resistance of the receiver varies inversely with the intensity of
infrared light being received.
The 555-astable timers receive signals from the receiver and its oscillation inversely proportional to the
resistance of the receiver. The number of oscillations is then counted by the binary counter, and decoded
by the binary decoder, and finally indicated by the display unit. The photograph of the A-m digital
densitometer is shown in Fig. 6 (a and b).
74
1.8
1.6
Density,Px (g/cm3)
1.4
1.2
1
0.8
Series1
0.6
0.4
0.2
0
0
2
4
6
8
10
Displacement, Rx (cm)
Figure 3: Liquid-density, float-displacement calibration curve
viii. Finally the A–m densitometer was used to measure the density of water, glycerol, paraffin oil,
and palm kernel oil. In each case 150ml of liquid was poured into the metal container, the float
carrying the receiver was then inserted, and the circuit completed to display the reading.
Other Important Densitometric Design Relationships Found:
(a)
 4V xd
4V Fx
 D 2  D 2
c
 c
When the value of the term 

 is greater than the value of Lc, liquid will over-fill


the container and spill out, a situation, which is undesirable.
(b)
The filling ratio (F.R.) of the container at any given condition is given by the following expression:
 4Vxd 4VFx 

 D 2  D 2  / Lc
c 
 c
F.R. = 
(c) To ensure floatation of the displacer the following condition must be fulfilled: L the value of Ldx
 4Vxd 4VFx 

 D 2  D 2 
c 
 c
must be less than of the term 
(d)
The minimum fixed volume of liquid in the container to ensure floatation is given by the following
expression:
4V xd

 L dx 
2
Dc
Vfxmin = 
 0 . 0796




  13



(ml)
75
IR – TX
Sensor
(Transmitter)
IR – RX
Sensor
(Receiver)
555 timer
Oscillator (Astable
timer) timer)
For impedance matching
Amplifier
Binary
counter
74192IC
Binary
7segment
Decoder
7447-IC
7segment
display
555 – Timer
(Monostable timer)
Figure 4: Block diagram of the digital densitometer circuit
Figure 5: Digital circuit diagram of the densitometer
76
Figure 6a: Front view of the densitometer
3.
Figure 6b: Side view of the densitometer
RESULTS AND DISCUSSION
The results of the measurement tests to determine the densities of water, glycerin, paraffin oil, and palm
kernel oil (pko) using the A-m densitometer are presented in Table 2.
Table 2: Results of tests done with the a-m digital densitometer
S/N Liquid Types
Densitometer Readings
Equivalent liquid density
g/cm3
1
Water
22.37
0.99
2
3
4
PKO
Paraffin oil
Glycerin
22.37
22.37
22.38
0.99
0.99
1005
The equivalent liquid density values obtained from the calibration graph shown in Fig. 7, or from the
calibration table (Table 3) are also shown in Table 2.
The densitometer does not give direct readings of liquid densities. In each case the calibration graph
(Fig.7), or the calibration table (Table 3) is used to generate the actual density readings.
77
22.44
Densitometer reading
22.42
22.4
22.38
Series1
22.36
22.34
22.32
0
0.5
1
1.5
Liquid density (g/cm3)
2
Figure 7: Densitometer reading/liquid density calibration curve
Table 3: Calibration table of the digital densitometer
Densitometer reading
Liquid density (g/cm3)
22.33
0.64
22.34
0.67
22.35
0.70
22.36
0.85
22.37
0.99
22.38
1.05
22.39
1.26
22.40
1.27
22.41
1.28
22.42
1.63
The analysis of the test results (Table 3.4) showed that the densitometer has a maximum error of +13.8%.
Table 4: Error analysis table for the digital densitometer
S/N
Liquid type
Densitometer Equivalent liquid
reading
density (g/cm3)
1
Water
22.37
0.99
2
P.k.o.
22.37
0.99
3
Paraffin oil
22.37
0.99
4
Glycerin
22.38
1.05
PKO – Palm kernel oil
Actual liquid density
(g/cm3)
0.96
0.88
0.87
1.06
Error (%)
+3.13%
+12.50%
+13.79%
- 0,94%
Sources of Error in the Densitometer Readings were identified to include:
(i) External light source: The digital densitometer was designed on the assumption that the receiver
(IR-RX) receives radiations only from the transmitter (IR-Tx). Therefore, any external radiation
sources would introduce error into the system.
(ii) Change in the position of the receiver: The densitometer was designed also on the assumption
that the receiver would receive all radiation from the transmitter during each measurement set-up.
And that is why the receiver is made to point to the transmitter. This, therefore, implies that any
shift in the position of receiver out of the focus of the transmitter would introduce error in the
measurement system.
78
(iii) Incorrect volume of liquid: The densitometer was designed to use 150ml (150cm3) of liquid for
density measurement. Any volume, more or less than this volume would create an error in the
measurement system.
4.1 Conclusions
In this work, a densitometer was designed and constructed based on Archimedes Principle. A digital
circuit based on optical sensing principle was incorporated to digitalize the readings of the Densitometer.
The instrument was used to measure the densities of water, palm kernel oil, paraffin oil, and glycerin at
laboratory-room temperature of 33oC. It can, therefore, be used to compare different qualities of those
liquids based on their densities. It can also be used to measure densities of liquids within 0.64-1.26g/cm3
range. One of the objectives of this work was the development of a simple digital densitometer that could
be used to measure and indicate directly the density of liquids. This objective was not fully realized in this
work. The reason is mainly because the relationship between densitometer displacement (Rx) in liquids
and densities of liquids was found not to be directly proportional (Fig. 3), hence the non-proportionality
also noticed in Fig. 7. However, indirect readings were obtained with maximum errors of about 13%.
4.2 Recommendations
(i) The densitometer parts (the Alum-displacer and the metal container) could be made from smooth
walled materials to eliminate errors in the volume of liquids used or displaced.
(ii) A close-fitting centralizer (ring) could be used to centralize the Alum-displacer in the metal
container.
(iii) The densitometer framework and its digitization circuit need to be further simplified and
packaged to ensure that the receiver collects all the radiations transmitted by the transmitter
during measurements, and to achieve better accuracy.
(iv) A software/programmme could be written for suitable microcontroller application that could
correct all the above limitations of this work and thus display the accurate digital value that will
directly indicate the density of every fluid.
REFERENCES
Hoeppner, C. H. and B. G. Liptak 1995a. Liquid Density: Application and Selection. In: Bela a Liptak
(ed). Instrument Engineers Handbook, 3rd Edition (Process Measurement and Analysis). p. 607-611.
Hoeppner, C. H. and B. G. Liptak 1995b. Liquid density-Hydrometers. In Bela a Liptak (ed). Instruments
Engineers Handbook, 3rd Edition. (Process Measurement and Analysis). p. 617-618.
Turner, J. D. 1988. Instrumentation for Engineers. Macmillan Educational Publishers London.
79
DEVELOPMENT AND TESTING OF A BAMBARA GROUNDNUT
POD SHELLING MACHINE
1
N. I. Nwagugu1 and C. O. Akubuo2
Project Development Institute (PRODA), Proda Road, Emene Industrial Layout,
P.M.B.01609, Enugu Nigeria.
2
Department of Agricultural and Bioresources Engineering,
Faculty of Engineering University of Nigeria, Nsukka, Nigeria.
E-mail nwagugunneka@yahoo.com, akubuoclem@yahoo.com
ABSTRACT
A motorized Bambara groundnut pod sheller was designed, constructed and evaluated. The sheller was
designed to shell the nuts effectively and also to eliminate the drudgery associated with the traditional
methods of shelling legumes.
Some physical and mechanical properties of the pod relevant to the design of the sheller were studied.
Average values of the physical properties determined include sphericity 82.64%, geometric mean
diameter 1.64cm, volume 1.53cm3, specific gravity 1.01cm, surface area 7.10cm2, weight 1.52g and
moisture content 13.35% (w.b.) as the average of the three moisture tested .The rupture force was found
to be 6.9N The fan of the separating unit runs at a fixed speed of 1110rpm. The shelling unit operates at
an average speed of 790 rpm without much damage to the seeds. The performance of the sheller was
evaluated, and the following mean results were obtained: Throughput capacity of 26.09kg/h, shelling
efficiency of 66.3%, material efficiency of 75.89% at a speed of 1294m/s. The pods were shelled at three
different moisture levels; 10.68%, 13.71% and 15.68% to ascertain optimum moisture content for
shelling. Results revealed that the highest shelling efficiency of 70% was obtained at the pod moisture
content of 15.26% wb. It was also found from the analysis that there was minimum percentage
mechanical damage at 22.98% moisture content wb.
KEYWORDS: Vertical Plates, Bambara Groundnut Shelling Machine.
1. INTRODUCTION
Given the rapid rate at which the world’s population is currently increasing in relation to agricultural
production, the goal of many Nigerian researchers must be to increase the productivity, not only for our
main crops, but also of certain crops that have hitherto been neglected especially in mechanization of their
post harvest operations. Among the latter group of crops that needed mechanical post harvest operation,
particular attention should be focused on the Bambara groundnut, (Vigna subterranean (L.) verde), which
flourished before the introduction of the peanut (groundnut), Arachis hypogea, (Goli et al 2004). Bambara
groundnut is believed to have been domesticated in West Africa from its presumed wild ancestor, Vigna
Subterraea var. spontanea (Herms) Hepper (Smart 1990). Threshing and grinding are based on empirical
methods with very little, if any of the knowledge of the mechanical properties of the material being used
in the design and analysis. (Mohsenin, 1986). Mechanical properties of biomaterials are significant in
quality evaluation and control, in determining the maximum allowable load for minimizing product
damage and minimum energy requirement for size reduction (Ezeaku, 1994).
Several researchers have investigated the physical and mechanical properties of many grains considered
relevant to the design of suitable machineries and equipment for processing them. Such report includes
physical properties of soybean by Nwakonobi et al (2003), soybean (Hall, 1974), Sheatnut by Aviara, et al
(2002), and Makanjuola (1975) etc. Some of our local crops have received similar research attention but
a great deal have not been studied on their pods. In much of Africa, Bambara groundnut ranks third in
importance after groundnut and cowpea (vigna unguiculata) but until recently, has received scant,
research attention despite its potential as a food crop. Bambara groundnut as an export crop is essentially
80
grown for human consumption. Bambara groundnut has long been used as an animal feed, and the seeds
have been successfully used to feed chicks, (Oluyemie et.al., 1976). The seed makes a complete food, as
it contains sufficient quantities of protein, carbohydrate and fat. Several researchers have examined the
bio-chemical composition of the seed, (Oluyemie et al. 1976, Oliveira 1976; Iinnemann, 1987; Ezeaku,
1994), Akubuo and Uguru 1999). On the average, the seeds were found to contain 63% carbohydrate,
19% protein and 6.5% fat. In Nigeria, most of the Bambara groundnuts produced are consumed locally
and in different forms. No industrial use of the crop has been reported according to Tanimu et al (1999).
A personal survey carried out in (Nsukka, Enugu state, Nigeria,) during the course of work showed that
the crop is mostly cultivated by small farmers in an intercropped system, on small patches of land owing
to the crop’s labour-intensive, shelling process. Farmers have shown little interest in the crop and its
commercial production due to the drudgery that is involved in the local shelling process. In commercial
production, grinding was the only aspect that has received serious machine attention in different designs.
The low level of production notwithstanding, milling and dehulling processes, can be attributed to
inefficient post-harvest handling and processing techniques, machines and structures.
As a leguminous crop that holds promises for the future, there is then a need to improve and conserve the
quantity and quality of Bambara groundnut. Through this study therefore, the design, manufacture, and
use of efficient effective handling techniques, machines and structures will enhance its economic
importance and boost food production. It is therefore, hoped that the results of this study, if judiciously
utilized will help to ease the labour associated with shelling. This would enable the high potentials of the
crop to be exploited.
The specific objectives of this research work were to design a machine that will shell and separate
Bambara groundnut pod from the nuts efficiently and to evaluate the machine based on its performance
under three different moisture contents, wet bases.
2. MATERIAL AND METHOD
2.1 Description of the Bambara Groundnut Sheller
The shelling of Bambara groundnut pods using this vertical plate model Fig.1 is carried out in three
separate operations, namely, the rubbing or squeezing of the pods just enough to remove the seeds from
the pods, the separation of the seeds from the chaff and finally the power source. The design consists of
two vertical plates (one stationary and the other reciprocating up and down) as the shelling mechanism.
This design is different from the conventional concave and drum types.
The shelling unit is most important part involved primarily in the shelling operation of the pods. It is
made up of the hopper, the shearing unit and the separating unit. The machine has a shaped hopper of
cross sectional area of 857cm and volumetric flow rate of 0.0121m3/s. Using shelling plate diameters
200mm width and 255mm length with a thickness of 41.4mm for shelling surface, a clearance was
created. This clearance between the stationary shelling plate and the reciprocating plate was gotten using
the maximum diameter of the pod 1.98cm and the minimum of 1.38cm from top to the bottom.
81
Fig 1 The bambara groundnut sheller
2.2 Pretreatment of Pods
The pod that was used for the test running of the Sheller was soaked in water to determine the optimum
shelling conditions that will be suitable for the shelling machine. This was done under three different
moisture contents of 10.68 % for (3 minutes) soaking, 13.71% for (5 minutes) and 15.68% for (7 minutes)
soaking respectively. The sample of the pod used is as shown in Fig .2
Fig. 2 Samples of Bambara Groundnut Pod used to test the Sheller
2.3
Testing of the Shelling Machine
The machine was tested in the Department of Agricultural and Bioresources Engineering Fabrication
Workshop University of Nigeria Nsukka. The test was carried out in two different stages. Stage (1), the
82
free test run (without load) and stage (2), testing with load (i.e bambara groundnut pods) under different
moisture contents (i.e 3minutes soaking 10.68%, 5minutes 13.71% and 7minutes 15.68%) at shelling and
different weights of (1000grams, 700 grams and 500 grams) respectively. Each test was done 9 times for
the individual weights i.e. 3 times each for each moisture level. A stop watch and a weighing balance
were used to ascertain the duration of shelling and measuring the quantity of unshelled bambara
groundnut pods, receptively. Analysis was carried out to determine the effect of moisture content and
shelling efficiency of the machine and also to see if speed affects percentage damage.
2.3.1 Free Run (Without Load) on the Machine
The machine was set to run at a speed of 1110rpm, freely without any load for about 10mnutes to check
for any abnormality or malfunctioning before the actual test with load was done.
2.3.2 The Actual Test with Load (Bambara Groundnut Pods)
Bambara groundnut pods of about 1000grams were fed into the hopper and were held from leaving the
hopper chamber through the help of a protective slot. The slots direct the pods entrance into the action
zone. After shelling, the wholesome groundnut seeds collected were weighed, using the weighing
balance. Also weighed were the damaged seeds. The test was repeated three more times with 700gram
and 500grams of bambara groundnut pods, using the same procedure under 3 different moisture contents
15.68% 18.71%and 21.68%.
The performance of the shelling machine was evaluated in terms of throughput capacity (kg/h), shelling
efficiency (%), material efficiency (%) and percentage damage (%) using equations 1, 2, 3, and 4
according to Maduako et al., (2006) respectively:
Throughput capacity (kglh) =
QS
TM
Machine Shelling efficiency (%) =
(1)
Qs  Qd
Qt t
Qu
x 100
Qu  Qd
Qd
Percentage Damage (%) =
x 100
Qu  Qd
Material efficiency (%) =
(2)
(3)
(4)
Where: Qt = total mass of shelled & unshelled pods, Tm = time of shelling operation (h), Qs
shelled pods (kg), Qu = mass of undamaged seeds (kg), Qd = mass of damaged seeds (kg).
=
mass of
Note that:
Qs = Ws + Wu
Qt = Ws + Wu + Wu
Ws = Qu + Wd
3. RESULTS OF PERFORMANCE EVALUATION OF THE SHELLER
The results obtained during the testing of the shelling machine with okpotokpo variety of bambara
groundnut pod are shown in Table 1. The results are also shown in the same table as the machine
performance parameters calculated.
83
3.1
Throughput Capacity (Kg/H)
The throughput capacity of the pod sheller was found to be 40.67%, 27.33%, 10.28% on the average for
the mass of pod fed into the hopper under the individual moisture contents (%) wet basis as earlier on
stated. From the performance table, Table 1, it was found out that 3minutes soaking irrespective of the
mass of pod fed has the best throughput capacity shell of 40.67kg/h than 5 and 7 minutes as evidenced by
the machine’s highest throughput capacity.
3.2
Shelling Efficiency
Shelling efficiency was found to be 66 % on the average. For 3 minutes soaking of 15.68% moisture
content introduced into the Sheller, as shown in the table, has the highest shelling efficiency of (72%).
This result indicates that this is the best moisture content the bambara groundnut should attain before the
developed Sheller can give its best without causing serious damage to the pods. However, it compares
favorably with those of Simobnyan cylindrical bambara groundnut Sheller (81%) and 80% as reported by
Atiku et al (2004).
3.3
Material Efficiency
The material efficiency of the Sheller was found to be 75.89% as shown in the table. The shelling
machine was seen to be very consistent in the quality of shelled bambara groundnut seeds. Looking from
the fact that its material efficiencies for the number of runs under different moisture contents is consistent
from 72.67% for 3 and 5 minutes soaking, but for 7 minutes soaking, it increased to 82.33%, showing that
the shellers material efficiency, the quality of its material handling and end product is almost maintained,
no matter the weight and moisture content.
3.4
Percentage Damage
The mean percentage damage of the sheller under the individual weight and moisture contents was found
to be 40.67%, 27.33%, and 10.76% respectively as shown in the table 1. The average percentage damage
of 22.98% obtained with this pod Sheller is very commendable since this is the first time this kind of
model is being developed. However, the analysis shows that the pod Sheller runs at a constant speed.
Therefore, as the moisture contents increases, the percentage damage decreases.
4.1 Conclusions
A motorized Bambara groundnut pod Sheller was designed constructed and tested using available local
materials. The following conclusions were drawn from the results of this investigation:
a. Water cannot be used as a medium of Bambara groundnut pod transportation; since its density is
slightly less than that of the pod. Thus, a fluid of higher density should be used. On the other hand,
water can be used to separate it from foreign materials that are lighter than the pods.
b. The shelling efficiency from the machine test was 72% at the moisture content of 10.68%wb
c. The percentage of shelled and partially shelled was moderate, when the Bambara groundnut pods
were shelled at 13.71% moisture content wb.
d. It was observed from the performance data that the machine has very little of shelled nuts at
15.68% moisture content (w.b). This means that shelling and separation efficiencies decrease as the
moisture content decreases.
e. Percentages of partially shelled pods and unshelled pods increased with increase in moisture
content.
84
Table 1: Performance Data of the Bambara Groundnut Pod Shelling Machine
Moisture
Content,
(%) Wb
10.68
3mins
Mean
STD
13.71
5 mins
Mean
STD
15.68
7 mins
Mean
STD
Mass of
Pod fed
into the
hopper
(g) Qt
(i) 1000
(ii) 700
(iii) 500
733.33
251.66
(i) 1000
(ii) 700
(iii) 500
733.33
251.66
(i) 1000
(ii) 700
(iii) 500
733.33
251.66
Mass
of
shelled
Pods
(g) Ws
720
510
400
543.33
162.58
680
480
380
513.33
152.75
660
460
380
500
144.22
Mass of
Pod
removed
(g) Wh
Mass of
unshelled
Pods (g)
Wu
Time of
Shelling
(s) Tm
Mass of
undamaged
seeds (g) Qu
Mass of
damaged
seeds (g)
Qd
Percentage
damage
seed, (%)
Through
put
capacity
(kg/h)
Shelling
efficiency
(%)
Material
efficienc
y (%)
180
130
60
123.33
60.28
180
70
50
100
70
160
160
70
130
51.96
100
60
40
66.67
30.55
140
90
70
100
36.06
180
80
50
103.33
68.07
66
58.8
46.8
57.2
9.70
88.2
82.8
79.2
83.4
4.53
87
79.8
76.8
81.2
5.24
470
360
320
383.33
77.68
500
350
270
373.33
116.76
540
380
310
410
117.90
230
150
80
153.33
75.06
180
130
120
143.33
32.15
120
80
70
90
26.46
33
29.4
20
27.47
6.71
26.4
27
29
27.47
1.36
18
17
16
17
1
49
38
35
40.67
7.37
35
27
20
27.33
7.51
0.34
0.28
0.22
10.28
0.06
59
64
72
65
1
64
62
66
64
0.58
72
65
72
70
4
67
71
80
72.67
6.66
74
73
71
72.67
1.53
82
83
82
82.33
0.58
85
4.2
Recommendations
Based on the results obtained and the conclusions arrived at, the following recommendations are hereby
made;
a. The shelling machine could be used to test for different varieties of bambara groundnut, so as to be
able to come up with other standard operating parameters.
b. Based on the results obtained in Table 1, it is recommended that shelling the bambara groundnut
pod when the moisture contents is at 15.68% wb will be more appropriate for a better result without
much injury to the seeds. However, the machine should also be evaluated with moisture contents
less than 15.68%.
c. The machine evaluated could be made to carry a wider shelling plate for more efficient shelling.
d. From the overall performance indices of the shelling machine, the Sheller is recommended for
small and medium scale bambara groundnut farmers.
e. A complete performance of the machine should be done based on speed. This is one of the major
limitations of this work. Since this first test was done with a fixed speed, It is recommend that the
machine speed be varied.
REFERENCES
Akubuo C.O. and Uguru M.I. 1999. Studies on the nutritive characteristics and fracture resistance to
compressive loading of selected bambara groundnut lines. Journal of the Science of food and
Agriculture 79:2063-2066
Atiku A A., Aviara N A., and Haque M. A., 2004. Performance evaluation of a bambara groundnut
sheller. Agric. Eng. Int.:the CIGR J. Sci. Res. Develop., P- 04002, VI, July.
Aviara, N.A, Gwandzara, M.I and Hague, M.A. (2002) physical properties of guna seeds. Journal of
Agricultural Engineering Research, 73(2); 105-111.
Ezeaku, C. A. 1994. Fracture characteristics of Bambara Groundnut (Vigna subterranean F (Ls) verdc) in
compressive loading. An M.Eng project report Department of Agricultural Engineering University of
Nigeria Nsukka.
Goli, A.E. 2004. IPGRI, cotonou, Benin coudert, M J 1984. Market openings in West Africa for cowpeas
and Bambara groundnuts. International trade forum 20(1)! 14, 15, 28.29.
Hall, A.S; Holowenko A.R.; Laughlin, H.G.(1976): Theory and Problems of Machine Design S I (Metric)
Edition. Shamus outline series McGraw Hill Book Company.
Linnemann, A.R. 1987. Bambara groundnut (Vigna subterranea (L.) Verdc.): a review. Abstr. On
Tropical Agriculture 12(7).
Maduako, J.N, M, Mathias, Vanke, I. Testing of An Engine Powered groundnut Shelling Machine.
Journal of Agricultural Engineering and Technology (JAET), Volume 14, 2006.
Mohsenin, N.N. 1986. Physical properties of plant and animal materials. Gordon and Breach Science
Publishers.6th Edition. New York.
Nwagugu, N.I. 2009. Development and testing of Bambaara groundnut pod shelling machine. An
unpublished M.ENG Thesis. Department of Agricultural and Bioresources Engineering. University of
Nigeria, Nsukka.
Nwakonobi, T and Idike, F.I. 2003. Physical properties of soybean. Journal of agricultural engineering
Technology. Vol 7(3), 2003 23-27.
Oluyemi, J.A, B.L fetuga and H.N.L Endeley, 1976. The metabolically energy ileum
Oliveira, J.S. 1976. Grain legumes of Mozambique. Trop. Grain Legume Bulletin. 3:13-15.
Smart, J. 1990. Grain legumes. Cambridge University press. Pp. (160-165).
Tanimu, B.S.A. & L. Aliyu, 1999. Genotypic variability in bambara groundnut cultivars at Samaru. In:
Proceedings of the 17th Annual Conference of the Genetic Society of Nigeria, pp.54-56.
86
STATUS OF AQUACULTURAL MECHANIZATION IN SOUTH EASTERN NIGERIA
C. C. Anyadike1; S. C. Duru2 and O. A. Nwoke3
Department of Agricultural and Bioresources Engineering, University of Nigeria, Nsukka, Nigeria.
Chinenye.anyadike@unn.edu.ng1; chi4jessy@yahoo.com2; nwoke.oji@unn.edu.ng3
ABSTRACT
The levels of mechanization of some selected fish farms in some states in South East of Nigeria were
investigated. Structured questionnaire was used to establish the socio – economic characteristics,
educational level, technical knowhow of the fish farmers set. The inventory of the farm machinery was
also established at each of the farms visited. Agricultural mechanization index was used to evaluate the
level of aquaculture mechanization. The results of the farm mechanization index study revealed that the
average level of aquaculture mechanization in South Eastern States is low. In order to improve the
situation, training, access to funds and technology are suggested.
KEYWORDS: Aquaculture, fishery, mechanization.
1. INTRODUCTION
Fish is an important source of protein for the world's growing population and the increasing demand for
aquacultural products has pushed the fishery industry to an economical tipping and near collapse of the
marine environment, hence the limited supply of wild fish. Aquaculture represents an opportunity to
increase seafood consumption worldwide and is currently one of the fastest growing industries all over
the world. This industry has the potential to become a major source of affordable, sustainable and healthy
nourishment for a growing human population in Nigeria. Fish being a good rich source of some aminoacids, vitamins, minerals and poly-unsaturated fatty acids not found in other sources of fat from aquatic
environment. Its harvesting, handling, processing, storage and distribution provide livelihood for millions
of people as well as providing valuable foreign exchange earnings to many countries (Al-Jufaili and
Opara, 2006). These potentials can only be achieved if farmers and fishermen are provided with
production and processing technologies that increase production and add value to their crops. The
development of fishing machinery and techniques that can be employed for effective fish, handling,
harvesting, processing and storage can never be over-emphasized especially in this age when aquaculture
development is fast gathering momentum in Nigeria (Akinneye et al., 2007).
Agricultural Mechanization in Nigeria can be classified into the hand tool technology, animal-draught and
engine power technology. Hand tool technology is the lowest level of mechanization. It refers to tools
and implements that rely on human muscles as the prime mover. Such tools in aquaculture include hook
and line, dragnets, fish nets, fishing baskets and fishing traps. Engine powered machinery technology
consists of a range boat used as mobile power for aquacultural operation. It also includes all those
machines that use power source for its operation in feeding, harvesting, processing, storage and
preservation of aquatic animals. More than 90% of farm operations in Nigeria are carried out using farm
tools (Anazodo et al., 1989). However, in aquaculture, mechanization can be classified into two broad
areas; namely manual powered and engine powered. The major operations undertaken in a fish farm
include hatchery and grow out, fish feed production and post harvest processing.
The need for mechanized fish farming, feed productions and post harvest processing has drawn the
attention of National Agricultural Research to devote utmost interest and resources to engineering
research in operations to minimize the drudgery, reduce labor intensities and unsanitary and inherent
unhygienic handling that are involved in the traditional manual operations (Davies, 2006).
Aquacultural mechanization is the development, introduction and use of mechanized assistance of all
forms and at any level of technological sophistication in aquacultural production. It involves the design,
87
development, operation and maintenance of prime movers and devices for aquatic environment
development, crop and aquatic animal production, processing and storage. Adequate aquacultural
mechanization will achieve the following; improved timeliness and precision, reduction of drudgery,
improved dignity of the worker/personnel, improved commercial quality and storability of fish production
and increased productivity. This will cause fish production to increase from the present level to hence
satisfying the human protein need, creating adequate employment, improving socio-economic needs of
the people and boosting the nation’s economy. It will also increase the awareness of fish potentials to
develop non traditional fish products for raw materials in the food and pharmaceutical industry.
The objective of this study is to assess the fish farms in South-eastern Nigeria, with a view to ascertaining
the mechanization levels in their farm operations. This will help in recommending the way forward.
2. METHODOLOGY
The study was carried out in four states in South Eastern Nigeria; Anambra, Ebonyi, Enugu and Rivers
States. A total of 30 farms were selected and visited. Table 1 shows the number of farms visited in each
State. The survey was carried out by means of a structured questionnaire and was administered to the
manager of the farms directly. Some of the issues addressed included the methods of fish farm
construction, operations, feeding, harvesting, processing and storage techniques.
Table 1: Number of farms per state visited
State
Number of farms visited
Anambra
7
Ebonyi
3
Enugu
7
Rivers
13
Total
30
All questionnaires administered were recovered (100% returns). Data was deduced from the filled
questionnaires and mathematical representation was adopted to ensure clarity and precision. The data was
analysed using descriptive statistics such as percentages, frequency distribution and graphs.
Mechanization index and levels were used to ascertain the level of mechanization in the selected states.
The mechanization levels were low, fair, and high. Low mechanization level means that manual power
used exceeded 33%. Fair means that animal power utilization ranges from 34% to 100%. High means that
mechanical power utilization ranges from 67% to 100% (Rodulfo, et al, 1998). Table 2 defines the
mechanization levels for aquaculture (fisheries), while Table 3 presents the mechanization index used in
the study.
Table 2: Definition of Fisheries Mechanization Levels
Mechanization Index
Definition
Low
1
Manual
2
Man + Hand tools
Intermediate
3
Man + Simple machines
4
Man + Powered machines
High
5
Man + Large powered machines + automated systems
88
Table 3: Mechanization Indices for Aquaculture (fisheries)
INDEX
Low
mechani
zation
Interme
diate
mechani
zation
High
mechani
zation
Feed
Preparation
Commercial
feeds/manual
size
modification
and mixing
Either size
reduction or
mixing is
motorized
Both size
reduction and
mixing are
motorized
Feed
Storage
Bags
Cans
Feed
Discharge
Manual or
hand
feeding
Silos
Small
automated
feeders
Electric
powered
storage
machines
Large
automated
motorized
feeder
systems
Harvesting
Hook and
line,
fishing
baskets,
Drag nets
Low-Power
operated
equipment
HighPower
operated
equipment
Pond
Drainage
Manual,
Gravitational
Fish
Processing
Grills and
stoves, sun
drying
Pond
Construction
Manual
excavation
Water
Supply
Manual,
Gravity
Motorized
(pumping)
slow
Drying
machines
Small
mechanical
machinery
Pumping
machines
Highly
motorized
piping
network
Fast drying
machines
Using heavy
equipment to
excavate
Pumping
and
filtering
machine
3.1 Characteristics of the Respondents
The study showed that 76% of the respondents were full-time farmers, 6.7% of the respondents were part
time and another 6.7% were local politicians within the state. 93.3% of the respondents were male while a
meagre 6.7% were female. The education level among the respondents show that 93.3% of them
achieved tertiary education while 6.7% acknowledge having passed through secondary school. This
means they can readily accept and adapt to changing trends. These statistics indicate that aquaculture is
gradually getting attention of the society even from people of other walks of life. The years of experience
of the fish farmers are presented on Figure 1.
50%
45%
Respondents (%)
40%
35%
30%
25%
20%
15%
10%
5%
0%
0 - 2 yrs
3 - 5 yrs
6 - 10 yrs
11 - 20 yrs
above 21 yrs
Years of Experience
Fig. 1: Graph showing years of experience of respondents
89
3.2 Level of Aquaculture Mechanization
Mechanization indices were defined for each commodity production/post-production operation and used
to evaluate the mechanization levels (see Table 2.) determined for the respondents. Table 3 specifies the
mechanization indices by production/post-production operation. The definitions highlight the
concentration of mechanization in the harvest/transport operation and the relative insignificance of other
activities as those related to the processing of the harvest produce. It was also based on the use of manual
methods or mechanical equipment for the respective operations (pond preparation, water supply, aeration,
harvesting, etc.).
Figure 2 indicates the mechanization levels for Rivers, Enugu, Anambra and Ebonyi States. Generally,
fish farming operations mechanization in the four States were low with respect to nearly all production
operations. This shows that human power dominates farm operations in all the fish farm investigated.
Although, intermediate levels of mechanization were applied in water supply, and feed discharge.
However, Ebonyi State rated the lowest, followed by Enugu and Anambra State. The mechanization level
of fish farms in Rivers State, though in the intermediate level for some operations were better than other
three investigated States.
3.3 Reasons for Low Mechanization
The lack or low mechanization observed is consistent with the predominance of the small-scale or
homestead fish farming in the areas. The economic status of the farmers is also an important factor that
determines the mechanization requirement and its affordability to the farmers.
Among the small fish farmers, lack of capital and or expertise to elevate production activities to
commercial levels is noted to be a major modernization constraint.
Hence, fish farm in south eastern Nigeria is still dependent on manual labour. The mechanization level is
relatively low.
3.4 Suggestions for Improvement
The study shows that the entire value chain for aquaculture in Nigeria namely feed production, fish
production, fish processing, handling and marketing, storage, infrastructure for mechanized production is
still dominated by low technology input resulting in very low level of mechanization. In order to improve
on this there is need for more training for fish farmers and processors as well as marketers. In addition,
there is need to make it easier for fish farmers to have access to low cost funds which will enable them
buy machines to improve their productivity. A special intervention fund is advocated. Researchers
should be encouraged to develop more local technologies for fish farming and processing.
90
Low
14
Intermediate
12
High
Number of Farms
10
8
6
4
2
0
Rivers
Enugu
Anambra
Ebonyi
Figure 2: Summary of Mechanization Levels
91
4. CONCLUSION
The mechanization levels of fish farm operation in South east, Nigeria were quantitatively evaluated. In
spite of the increased awareness and interest in aquaculture, the study recorded a very low mechanization
level in all the investigated State compared to Asian countries. However, farms in Rivers State fared
better than other states since their mechanization were at the intermediate stage in most operations.
REFERENCES
Akinneye, J. O. Amoo, I. A. and Arannilewa, S. T. 2007. Effect of drying methods on the nutritional
composition of three species of (Bonga sp, Sardinella sp and Heterotis nilotilus). Journal of Fisheries
Int 2(1):99-103.
Al-Jufaili, M. S. and Opara, L. U. 2006. Status of fisheries Postharvest Industry in the Sultanate of Oman:
Part1 Handling and Marketing System of Fresh Fish. Journal of Fisheries International 1 (2-4):144149.b
Anazodo, U. G. N., T. O. Abimbola and J. A. Dairo. 1987. Agricultural machinery use in Nigeria. The
experience of a decade (1975-1985). Proc. Nigerian Society of Agricultural Engineers, pp 406 – 429.
Rodulfo, V. A.; Amongo, RM, C.; Larona, MV. L. 1998 Status of Philippine agricultural mechanization
and its implication to global competitiveness. Philippine Agricultural Mechanization Bulletin, 5(1):313.
Davis, R. M. 2006. Mechanization of Fish Industry in Nigeria: Status and potential for Self-sufficiency
Industry in Nigeria: Status and potential for Self-sufficiency in Fish Production. A paper presented at
a one-day workshop on intensive fish farming. 19th August, pp10.
92
MODELING HOT AIR DRYING CHARACTERISTICS OF RED
BELL PEPPER (Capsicum annum. L)
1
A. L. Musa-Makama1 and Mohammed Abdullahi2
Agricultural Engineering Department, Federal Polytechnic, Bida, Niger State, Nigeria
makamamusa@yahoo.com
2
Chemical Engineering Department, Federal Polytechnic, Bida, Niger State, Nigeria
ABSTRACT
The drying kinetics of pretreated red bell shaped pepper Capsicum annum. L (untreated, steam blanching
and dipping in 10% (v/v lime juice solution) in a convective hot air dryer were studied at 50°C and 1.5m/s
air flow. The drying of bell pepper occurred in the falling rate period. It was found that pretreated bell
pepper slices dried faster than the untreated with percentage decrease of 14.28% and 21.42% in drying
times of untreated samples for lime dipped and steam blanching respectively. Four (4) thin-layer drying
models were fitted to the experimental moisture ratio data. The models were the Newton, Henderson and
Pabis, Page and the Logarithmic models. The best fit model was selected by comparing the values of the
correlation coefficient, R2; the chi-square, χ²; and the root mean squared error, RMSE. Among the models
evaluated, the Henderson and Pabis model satisfactorily described the drying behavior of the untreated
bell pepper having the highest R2 and the lowest χ² and RMSE. The Page model satisfactorily described
the drying process of pretreated bell pepper better than other models. The effective diffusivity of
pretreated pepper was higher. The drying parameters and modeled behaviors of the drying process are
important inputs in the effective design of dryers for bell pepper.
KEYWORDS: Bell pepper, pretreatment, mathematical models, drying, diffusivity.
1. INTRODUCTION
The bell shaped pepper (Capsicum annum L) popularly called “Tatase” in Nigeria belongs to the
solanaceae family with Mexico as probably its origin. It is a fast growing annual herb with large 3-12cm
diameter inflated non-pungent fruits which have much sweet aroma and taste when mature. Pepper is
majorly grown in the Northern part of Nigeria between latitude 10’ N and 12’ 30’ N particularly under
irrigated farming, with some quantity produced also in the Southern part of part in the rainy season as rain
fed crop.
Fresh bell pepper fruit (Tatase) contains per 100g edible portion: 86 – 93g water; 0.86 – 2.0g protein, 6.64
– 10g carbohydrate, 1.7 – 2.6g dietary fiber, 2.4g total sugar. It is very rich in potassium (175mg)
phosphorus (20mg) and calcium (10 – 29mg) and iron (2.6mg) per 100g. Matured red capsicum annum
contains about 80 – 140mg/100g vitamin C and 2,760ug and 180ug vitamin A in red and green pepper
respectively. (Faustino et al. 2007; Taheri-Garavand et al., 2011) The high nutritional values gives the
bell shaped pepper its tremendous use in soups and stews. In different parts of the world, pepper is used
for different medicinal purposes. In Nigeria, it is used internally as stimulant and carminative, and
externally as counter irritant (Gruben and Tahir, 2004; Idowu et al, 2010).
The Food and Agricultural Organization (FAO) of the United Nations estimated world production of
pepper as 21.3 million tons in 2001 and 24 million tons in 2005. Production in Africa was estimated at 1.0
million tons being the largest producer and accounting for over 50% of production (715,000 tons) from
90,000 hectare in 2001 compared to 695,000 tons from 77,000 hectares in 1983 (FAO, 2003; Idowu et al,
2010) . Fresh pepper has a short shelf life due to its high moisture content, and the major way of
preservation is by drying. FAO reports that about 50,000 metric ton of pepper was dried in Nigeria in
2009 FAO (2010). Drying of pepper is done majorly by rural farmers using the open sun drying method.
This takes not less than five days depending on the weather condition to bring moisture in pepper to
required 4 – 11% (wb) safe for storage. This long period of time under direct exposure to air and light
93
results into low quality dried pepper and exhibited by low vitamin content, faded red color, development
of brown pigment. (Osunde and Musa-Makama, 2007; Candori et al, 2001).
The development and use of artificial drying systems with air temperature between 50 and 80’C have
been reported to reduce drying time and increased effective diffusion of moisture from inside to the
surface of pepper (Kaleemula and Kiallapan 2005; Di -Scale and Crapiste, 2002). But can also results into
loss of volatile compound, nutrient and color (Susana et al 2005; Wiriya et al, 2009). The enzymatic and
non-enzymatic reactions which occur during drying and responsible for low quality in the presence of
heat at intermediate moisture level can be prevented by pretreatments such as blanching and chemical
treatment (sulphiting and dipping) that inactivate enzymes (Wiriya et al, 2009).
Several studies have reported the use of pretreatment to prevent non-enzymatic browning reactions during
drying of fruits and vegetables at air temperatures between 40 and 80’C (Doymaz and Pala, 2002;
Sobukola 2005; Musa-Makama and Adgidzi 2004; Wiriya et al 2009) some other authors have used step
wise drying techniques using 20 – 50’C air, this also due to longer drying period can result in into mold
growth especially in fruits with waxy like skin like tomato, okra, and pepper (St George et al 2004). The
practice of water blanching could lead to destruction of heat sensitive nutrients like vitamin C and
aromatic materials, on the other hand, rural farmers are not accessible to chemicals for treatments such as
sodium metabisulphite, calcium chloride, calcium carbonate and so on which are used in research studies
due to cost and availability.
Drying is of a great importance in preservation and storage of pepper; while artificial drying systems have
the ability to control drying air condition, reduce crop losses, improve hygiene and quality of dried
product, however this must also be at low cost. This calls for a strong transition from traditional drying to
artificial, large scale dryers that are cost effective. There is therefore need to model drying process under
prescribed conditions so as to help optimization and effective design of dryers and improve existing ones.
Several studies on the influence of drying conditions on the drying kinetics and on quality characteristics
of pepper have been published (Taheri-Garavand et al., 2011; Faustino et al., 2007; KaymakErtekin.,2002; Tunde-Akintunde et al., 2005; Tunde-Akintunde and Ajala (2010); Sismal et al., 2005;
Vega et al., 2007). Empirical models were applied to red pepper and drying kinetics were examined. The
drying kinetics of red peppers using different pretreatments and drying air conditions was also studied by
(Doymaz and Pala, 2002; Sanjuan et al., 2003). There has been no literature report on steam blanching
and lime dipping pretreatment of bell pepper.
The objectives of this study are therefore to: study the effect of steam blanching and lime pretreatment on
drying kinetics of bell shaped sweet pepper; model the drying process and select a model that best fits and
describe the drying process under test conditions and determine the effective diffusivity of pretreated
pepper slices.
2.1 Raw Material and Pretreatment Procedure
Fresh ripe bell shaped pepper Fruits (Capsicum annum L) were obtained from a local farmer at Rogota
village adjacent to the Federal Polytechnic, Doko road, Bida Nigeria. The pepper fruits were selected,
washed under running water, drained and kept in a desiccator which was then put in a refrigerator at 20’C
to hold briefly. Fresh pepper fruits for each run were cut into 40mm ±0.5 length; 20 mm ± 0.5 breath
size, having an average thickness of 5mm± 0.5 thickness, Sample slice dimensions were taken using
vernier caliper.
94
2.2 Steam Blanching
Freshly cut samples were placed in a plastic colander which was then placed over saturated steam (from
water at 100’C in boiler) for 6minutes with intermittent turning of the slices. The samples were thereafter
allowed to drain and kept in a desiccator.
2.3 Lime Dipping
Fresh lime fruits were purchased from a local market in Bida town. The fruit were cut and the juice
extracted and strained to remove seeds. Lime juice was mixed with water (10% v/v) to constitute the 10
% lime pretreatment solution. Sliced fresh samples were soaked in the solution for 10minutes, and then
drained, dabbed with clean cloth before keeping in a desiccator.
2.4
Moisture Content Determination
Moisture content of both fresh and dried samples were determined using the American Society of
Agricultural Engineers standard S.358.1(ASAE, 1992) in a vacuum oven at 103°C. Moisture content of
fresh samples were determined before and after pretreatment and were calculated from equation (1)
below:
 W  W2
% M   1
 W1

100

1
Where M = moisture content wet basis (%) W1 and W2 are initial and final weights of samples (g)
respectively.
2.5
Drying Experiment
The study was carried out using a convective hot air tray dryer (Armfield, England) available in the Unit
Operations Laboratory of the Federal Polytechnic Bida. The system which has variable temperature (0 80’C) and air flow (0 – 3.0m/s) was set at 50°C and 1.5m/s airflow, turned on and allowed to run for 30
minutes so as to stabilize. During this period, temperature and airflow were monitored using a digital
temperature – humidity meter (model) and digital airflow meter(LCA 6000 Javac (UK) Limited) until
stable conditions were attained by constant values over several readings. The ambient air conditions were
also determined using these instruments. The temperatures of the inlet air were measured by a
psychrometer at the end of the duct before entering into the drying chamber. A given quantity of pepper
sample of known initial moisture content was weighed in an aluminum mesh tray 40cm x 20cm of preknown weight using a Mettler 2000 (Gibertini Electronics, Italy) digital weighing balance (capacity:
2000g; precision: 0.01g). The samples were loaded in a single layer batch of 3 – replicates and placed into
the dryer. Moisture loss was recorded at 20 minutes interval from commencement of drying by weighing
the samples using the weighing balance. Drying continued until moisture was reduced to 6% +0.1
thereafter, sample was dried to constant weight to determining the equilibrium moisture content. The
moisture content of dried sample after attaining constant weight was determined by keeping in oven at
103°C for 24hours initial and final moisture contents were calculated from equation (1) Moisture content
was computed from weight loss data using equation (2).
M=
Wt  Wd
( g / g dry
Wd
matter
)
2
Where Wt and Wd are weights (g) of sample at time t and weight of dry matter respectively.
The Drying rate and moisture ratio were determined using equations 3 and 4 respectively
DR 
dm M t  dt  M t

dt
dt
3
95
MR 
Mt  Me
Mo  Me
4a
The moisture ratio was further simplified according to Goyal et al., (2007) as
MR 
Mt
4b
Mo
Where Mt is the moisture content at time t, Mo and Me are initial and equilibrium moisture contents
respectively. All values were determine as mean values of three replicates and expressed as g water/g dry
matter.
2.6
Mathematical Modeling of Drying Curves
To select a suitable model for describing the drying process, the experimental data transformed into
moisture ratio using equation 4 were fitted to four (4) thin layer drying models shown in table 1.
Table 1: Thin –layer model equations
Model name
Model equation
Newton (exponential)
Henderson and Pabis
MR= exp(-kt)
MR =a.exp(-kt)
Page
MR=exp(-ktn)
Logarithmic
MR= a.exp(-kt)+C
These models are described as simplification of the general series solution of the Fick’s second law of
diffusion. The Page model which is a modification of the Newton (exponential) model is used to
overcome the shortcoming of the Newton model which often results into over prediction and under
prediction of drying rate of drying early and latter stages of drying of agricultural crops respectively
(Gupta et al, 2002). The empirical models are derived from the relationship between the water content in
the product and the drying time. It requires that the experimental curves be compared to the curves of
proposed models that can predict the behavior of the product during drying. These models amongst others
have been used satisfactorily for tomato (Kamil et al., 2005); red pepper ( Doymaz, 2004; Simsal et al.,
2005; Ebru and Yaldiz., 2004); okra ( Doymaz, 2005; and Kuiteche et al., 2007); Apples ( Goyal et al.,
2008); Opuntia fruit ( Amira et al., 2010).
2.7
Determination of Effective Diffusivities
The effective moisture diffusivities of treated and untreated samples were determined using Fick’s second
law. The moisture diffusivity of an infinite lab is given by the equation 6. (Garavand et al., 2011).
M
8
MR  t  2
Mo x
 2n  12  2 Defff t 
exp 


2
4 L2
n 1 2n  1



1
5
Where MR is the moisture ratio, Deff is the effective diffusivity (m2/s), t, is time (s) and L is the thickness
of the slices (m), n is a positive integer. Equation (5) is further amplified as below
  2 Defff t 
8
8
MR  2 exp 
  MR  2 exp kt 
2
x
x
4 L 

 2 Defff
where k = 
4L2
6
96
2.8
Statistical Analysis
Non-linear regression analysis was performed using the POLYMATH 6.0 software along with SOLVERan optimization tool (GRG2 method) included in the Microsoft Excel 2002TM spreadsheet. The coefficient
of regression R2 was the main criteria for selecting the best fit model equation. In addition to that, the
goodness of fit was determined by parameters such as the chi-square (χ2) and the root mean square error
RMSE. For best fit the R2 value should be highest and the χ2 and RMSE values should be lowest (Goyal
et al., 2006). These parameters can be calculated as below
n
2  
MR
i exp
 MRipred 
7
N Z
i 1
1
RMSE  
N
N
 MRi ( pred )
i 1

 MRi exp) 

1
2
2
8
3.
RESULTS AND DISCUSSION
3.1
Effect of Pretreatments on the Drying and Drying Rate of Bell Pepper
The drying process was stopped when samples attained 6% moisture content (wet basis). Weight loss data
were used to calculate the moisture content (dry basis). The moisture content data were converted to
moisture ration using equation 3.
The experimental moisture ratio with time curves for untreated and pretreated bell pepper dried at 50°C
and 1.5m/s airflow is shown in Figures 1. The drying curves showed that moisture content reduced with
increase in drying time and that the drying process took place in the falling rate period as the curves
indicated no constant rate drying. This means that the drying process was exceptionally a diffusion drying
process. Similar result has been reported for okra (Wilten et al., 2009); pepper (Taheri-Garavand., 2010;
Wiriyi et al., 2009).
UTS
1.1
LDS
1
SBS
0.9
Moisture Ratio
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
0
20 40 60
80 100 120 140 160 180 200 220 240 260 280 300
Drying Time (min)
Figure 1: Drying curves of untreated and pretreated bell pepper at 50°C and 1.5m/s
From Table 2 it is observed that pretreatment had effect on the drying process over time. The drying time
to reach moisture content of 0.07 g/gdm from initial average value of 6.61g/gdm was 280min, 2220min
and 240min for untreated, steam blanched and lime dipped samples respectively. Pretreatments decreased
drying time by 14.28 – 21.42%. Similar result was reported for steam blanching of pepper (TundeAkintunde et al., (2005), Doymaz and Pala., (2002), Seid and Hensel, (2011). The result also showed that
lime juice pretreatment can give shorter drying time for bell pepper than when untreated. At any given
97
moisture content, the drying rate of untreated sample was lowest, showing that pretreatment enhances
drying rate and reduces the drying time of bell pepper.
Table 2: Total Drying Time for Untreated and Pretreated Bell Pepper to Reach Final from 6.21g/gdm
Moisture Content using Air at 50°C and 1.5m/s
Treatment Final Moisture content Total Drying time % Decrease in drying time
(g.gdm)
(min)
UTS
0.09
280
SBS
0.07
220
21.42
LDS
0.07
240
14.28
0.09
0.08
UTS
LDS
Drying Rate (g/gdm/min)
0.07
SBS
0.06
0.05
0.04
0.03
0.02
0.01
0
0
20
40
60
80 100 120 140 160 180 200 220 240 260 280 300
Drying Time (min)
Figure 2: Drying rate vs. drying time curve for untreated and
pretreated bell pepper
0.09
UTS
LDS
0.08
SBS
Drying Rate (g/ gdm /min)
0.07
0.06
0.05
0.04
0.03
0.02
0.01
0
0
0.5
1
1.5
2
2.5
3
3.5
4
Moisture Content (g/gdm)
4.5
5
5.5
6
6.5
7
Figure 3: Drying rate vs. moisture content curves for untreated and pretreated
3.2
of Model
bell Evaluation
pepper
The moisture content data were converted to moisture ratio using equation 3. The experimental moisture
ratio curves are shown in figure 1. The moisture ratio data were fitted to the four (4) thin-layer models
shown in table 1 using the POLYMATH 6.0 software along with SOLVER- an optimization tool (GRG2
method) included in the Microsoft Excel 2002TM spreadsheet. The moisture ratio is reduced exponentially
with drying time which is typical of most fruits and vegetables (Sobukola, 2005; Hossain et al., 2004;
Taheri-Garavand 2010).
98
Table 3 shows the result of statistical evaluation of tested models while table 4 shows the values of
evaluated model parameters. The best model describing the thin layer drying was selected according to
the highest R² values and the lowest RMSE and χ² values. The data also shows that for both steam
blanching and lime dipping treatments, the page model gave a best fit with respect to R², χ² and RMSE
values. The values were highest for R² (0.9986 and 0.9926) for steam blanched and lime dipped samples
respectively; χ² = 0.00126 and 0.00670 and RMSE = 0.00322 and 0.00630 for steam blanched and lime
dipped pretreatments respectively. It follows therefore that the page model best predicts the drying
behavior of pretreated bell pepper samples. Similar result has been reported by Srinivasakannan and
Balasubramaniam, (2011). The Henderson and Pabis model best fit the untreated sample data with R ², χ²
and RMSE values being 0.9984, 0.00261, and fit model.
3.3
Effects of Pretreatment on Effective Diffusivity
The second Fick’s law of diffusion was used to determine the effective diffusivity as given by equation 6.
The estimated Deff values and drying constants for the various pretreatments are given in table 5. Effective
diffusivity was 1.26x10-10, 1.88x10-10 and1.547x10-10 for untreated, steam blanched and lime dipped
pretreatments with a coefficient of determination value of 0.9957, 0.9974 and 0.9954 respectively.
Untreated sample had the lowest value and steam blanched having the highest value. The values obtained
fall within the range reported by Taheri-Garavand, (2011) for bell shaped pepper (1.7x10-10 – 1.19x10-10)
and also for most vegetable crops
Table 3: Statistical Results obtained from selected mod
TREATMENT MODEL
R2
UTS
Henderson & Pabis
0.9984
Newton
0.9974
Page
0.9982
Logarithmic
0.9982
SBS
H&P
0.9965
Newton
0.9986
Page
0.9987
Logarithmic
0.9987
LDS
H&P
0.9834
Newton
0.9926
Page
0.9976
Logarithmic
0.9846
RMSE
0.004259
0.004301
0.004292
0.003593
0.005131
0.005366
0.003227
0.003036
0.009478
0.011388
0.006298
0.009110
χ²
0.002611
0.002660
1.2580
6.552
0.003185
0.01284
0.00126
0.03919
0.01518
0.02191
0.00670
0.4454
1.1
Exp SBS
1
Page SBS
0.9
Exp LDS
0.8
Page LDS
Moisture Ratio
0.7
Exp UTS
0.6
Henderson &
Pabis UTS
0.5
0.4
0.3
0.2
0.1
0
0
20
40
60
80
100 120 140 160 180 200 220 240 260 280 300
Drying Time (min)
Figure 4: Experimental and predicted moisture ratio versus drying time
by best fit model: Henderson and Pabis model for untreated and Page
model for pretreated.
99
Table 4: Values of the drying constants and coefficients of the best fit model for
untreated and pretreated bell pepper
Treatment Model
k
a
n
Deff (m2/s)
R2
UTS
Henderson &Pabis 0.01415 0.99404
1.26x10-10 0.9957
SBS
Page
0.0262
0.90738 1.88x10-10 0.9974
LDS
Page
0.02999
0.80197 1.547x10-10 0.9954
4.
CONCLUSION
Mathematical model of drying processes is important in the design and optimization of drying process. It
chiefly involves the determination of drying kinetics which describe the mechanism and influence that
certain process variables and techniques exert on moisture transfer. Drying kinetics of pretreated
Capsicum annum L samples were examined by introducing 4 empirical thin layer mass transfer models.
The models were fitted to experiments data obtained using a hot air convective tray dryer and analyzed
using non-linear regression analysis. Investigation involved two pretreatments: steam blanching and lime
dipping at air temperature of 50’C an d 1.5m/s flow rate. The drying time to reach 6% moisture content
(wb) from 87% (wb) was found to be (220– 280min), shortest in steam blanched sample and highest in
the control (untreated sample). From the regressing analysis of all models, it can be concluded that all the
models have good fit however; the page model best predict the behavior of pretreated samples while the
Henderson and Pabis model predicted untreated sample behavior best. The pretreatment showed drying as
taking place in the falling rate period having caused initial moisture reduction before drying.
Pretreatments also affect the effective moisture diffusivity. The effect of various temperatures should be
evaluated along with the pretreatment in order to estimate the activation energy. The data will be helpful
in design of systems for pepper drying that will enhance better quality at minimal cost than sun drying.
Nomenclature
χ²
reduced chi-square
a, c, n
empirical constants in drying models
DR
Drying rate
Deff
Effective diffusivity
k
drying constant
L
thickness of pepper, m
M
moisture content at time t, kg moisture.kg-1 dry matter
Me
equilibrium moisture content, kg moisture.kg-1 dry matter
Mo
initial moisture content, kg moisture.kg-1 dry matter
MR
dimensionless moisture ratio
MRexp
experimental moisture ratio
MRpre
predicted moisture ratio
N
number of observations
R2
coefficient of determination
RMSE root mean square error
t
drying time, min
Z
number of drying constants
W
weight
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102
BIOGAS PRODUCTION IN NIGERIA – POTENTIALS AND PROBLEMS
L.C. Orakwe1, E.C. Chukwuma1 and C.B. Emeka-Orakwe2
1
Department of Agricultural & Bioresources Engineering,
Faculty of Engineering, Nnamdi Azikiwe University, Awka, Nigeria;
E-mail: louiemek@yahoo.com
2
Agricultural & Bioresources Engineer based at Enugu, Nigeria.
ABSTRACT
This paper has discussed Biogas Production in Nigeria as an alternative energy source especially at this
crucial stage when oil prices are fast escaping the range of the common man. In addition the need to
ameliorate the generation of green house gases makes biogas technology inevitable. This paper thus
evaluated the problems and potentials of biogas production in Nigeria. There are quite encouraging
potentials for this technology while the associated problems are surmountable. Hence, extensive studies
and evaluation of the technology have to be carried out so that much of the constraints associated with its
adoption as a viable energy source can be overcome and much of the benefits realized. It is in this light
that the technology is being advocated as a viable alternative to power and energy source especially with
the current conditions associated with other forms of power and energy sources in Nigeria.
KEYWORDS: Biogas, substrate, waste, sludge.
1.
INTRODUCTION
The search for alternative and renewable sources of energy is assuming greater dimensions in the world
today. In the broad area of biomass energy sources, considerable research is currently going on with
regards to several means to exploit the energy potentials of otherwise waste materials such as residues
from crop production, primary and secondary agro – allied processing, wood work, human and animal
wastes. Indeed, in several countries, traditional energy sources are estimated to account for 50 – 70% of
the total energy demands (Anon, 1980; de Montalembert, 1983; Faborode, 1988). Notably however, fuel
wood alone is more dominant, accounting on a regional basis for 70% of the total domestic energy
consumption in Africa, 34% in Latin America and 30% in Asia; representing an enormous drain on the
forest resources in addition to the attendant environmental degradation. Whereas several tonnes of wastes
and residues are burnt annually or left to rot on the farms and factory dumps, these excess residues can be
utilized for energy generation purposes if advantage can be taken of technologies for material
densification (Faborode, 1988). Efficient utilization of waste and residues will definitely create a new
industry and boost the economy by making valuable assets out of costly waste.
One of the ways in which these wastes are utilized is in the production of biogas, notably methane which
is a combustible gas and, essentially the product of anaerobic fermentation of cellulose – containing
organic matter. Biogas technology is the technology associated with the production, collection, storage
and utilization of biogas and other products associated with biogas production. It represents one of a
number of village-scale technologies currently enjoying a lot of popularity among governments and
international aid agencies and also offers the technical possibilities of more decentralized approaches to
rural development. Although the benefits - social, economical and environmental are known, the technical
expertise is still lacking, hence, the danger of misapplication of the technology in the rural areas of the
third world. This situation thus necessitates further in depth studies, research and evaluation of the biogas
technology towards ameliorating rural energy demand and utilization. Lack of adequate data on both new
and traditional systems of biogas production generally make the system somewhat unreliable and before
any major commitments are made to the production of this form of energy, a much more systematic
approach to research development and evaluation be made (Barnett, et al, 1978).
103
The technical and economical evaluations that have been carried out so far have been applied only to a
limited set of the known techniques and comparisons have been made between biogas and other systems
at the “high” end of the technological spectrum. Given the current bias in the distribution of the world’s
research and development efforts, it is hardly surprising that in these comparisons the under-developed
small-scale techniques sometimes appear to be inferior. With the fluid state of biogas technology and the
unusual interest currently being shown in it, it would seem to be relatively easy to design and build biogas
plants that could be operated in rural situations to meet certain social objectives and yet compete
favourably with “higher” technologies even in conventional terms of profit and capital required per unit
output (Barnett, et al, 1978). This supposition is illustrated in Table 1.
Table 1: Main energy sources that could possibly be provided to rural areas
Energy source
Cooking Lighting
Heating
Power1
Transport
Electricity
(X)
X
X
Coke, Coal
X
Kerosene
X
X
X
X
Diesel
X
X
Gas
X
X
X
X
X
Wood
X
X
Straw, vegetable, X
X
waste
Crop residue
X
X
Dung
X
X
Solar energy
(X)
(X)
Hydro
X
Wind
X
Alcohol
X
X
Heat energy2
X
X
X
X
X
X
X
X
X
-
1
includes for example pump sets; 2 includes steam
Note: (X) represent methods that are likely to be very expensive, be of limited application or need further
development.
Source: Barnett et al (1978).
It is however essential to take cognizance of the local specifics, hence the viability of a particular
environment for biogas technology. This paper is thus an effort towards achieving this objective and the
need to examine the numerous potentials, benefits and utilization of biomass and consequently biogas to
meet energy and associated demands of rural people.
2.
SUBSTRATE SOURCES FOR PRODUCTION OF BIOGAS IN NIGERIA
As pointed out in the introduction, there is crucial need for in-depth research and evaluation of a project
such as biogas technology before getting involved with it. Despite its obvious attractive benefits, it is
however necessary to justify the associated socio-economic cum environmental implications. Evaluation
of the local specifics of an area will show how much of each available type of substrate is accessible to
the project and their suitability to achieve the desired goals. A comprehensive study and evaluation will
inter-marry the deductions and come out with the most viable design of a biogas generation system.
The probable substrates to be considered include the following:
a. human feaces
b. animal manure
c. domestic sewage
d. brewery effluent
e. food processing waste
- yam peel
104
- tomato canning industry waste
- fish processing waste
- meat processing waste
- others
f. water hyacinth
g. crop and vegetable residues
The above named substrates, though not exhaustive are the possible alternatives to consider in Nigeria.
Often times, such beneficial projects as biogas technology are hampered by an inadequate evaluation of
the sources and availability of raw materials usually based on the assumption that such raw materials are
in abundant supplies. This section thus tries to evaluate the availability, accessibility and suitability of
these substrates with respect to biogas production in Nigeria.
The availability of substrates in Nigeria is not questionable and ways of collection for biogas production
can always be arranged. An important consideration however is the suitability of the substrate to justify
the efforts of the biogas production. To illustrate this important consideration, Buswel and Muller, (1976)
produced a simplified overall picture of the anaerobic fermentation of a typical substrate (CnHaOb) to
carbon dioxide and methane. Their equation (although over simplified because the overall stoichiometry
neglects cell formation) show that:
n a b
n a b
C n H a Ob  H 2 O     CO2     CH 4
 2 8 4
 2 8 4
This composition shows the dependence of methane produced on the type of substrate and in principle is
predictable. The total gas yield, (CO2 + CH4) can be calculated because 1kg of carbon in the substrate will
yield 1/12Kmole gas product. In effect, per kilogram of carbon decomposed, the gas yield should be
(22.4/12)m3 gas (measured at STP) or 1.867m3 of gas (Buswel and Muler, 1976).
Based on this dependence on carbon content of the substrate, Buswel and Muller, (1976) derived the table
shown below to illustrate the gas yield of some substrates. It is assumed that none of the substrates leaves
the system as it also assumes that all the carbon in the feed is susceptible to anaerobic digestion. Hence,
the table is only a rough estimation of the effect of substrate on gas yield, since the assumptions do not
hold entirely. Based on the data from the Table 2, a conscientious study and evaluation of the viability of
each substrate is undertaken.
Table 2: Maximum gas yield (from various sources)
Substrate
N
C/N ratio C%
Feaces
40 – 55
Blood
10 – 14
3
30
Young grass
4
12
48
chippings
Lucerne
2.4 – 3
16 – 26
60
Grass chippings
2.4
19
45.6
Manure (large)
2.15
14
30.1
Seaweed
1.9
79
36.1
Oat straw
1.05
48
50.4
Wheat straw
0.3
138
38.4
Saw dust
0.11
511
56.2
Carbohydrates
Fat
Protein
Horse manure
2.3
25
57.5
Gas yield (ft3/lb Dm)
22.4 – 30.0
16.8 -23.5
26.9
Gas yield (m3/kg Dm)
13.9 - 19.6
10.4 – 14.6
16.68
33.5
26.5
16.86
20.2
28.2
21.5
31.5
12
23.1
15.7
32.20
20.77
16.43
10.45
12.5
17.5
13.33
19.53
7.44
14.32
9.73
19.96
105
Cow manure
1.7
18
30.1
Hay
4
12
48
Pig manure
3.8
20
76.0
Goat/Sheep
3.8
22
83.6
manure
Poultry manure
6.5
15
90
Garbage
3
54.7
Paper
40.6
Newspaper
0.05
40.6
chicken manure
3.2
23.4
Steer manure
1.35
34.1
Note: to convert ft3/lb to m3/kg multiply by 0.62
Source: Buswel and Muller (1976)
17.22
26.9
42.5
46.7
10.68
16.68
26.35
28.95
50.3
30.5
22.8
23.8
13.2
19.1
31.19
18.91
14.14
14.14
8.18
11.84
Availability of substrates is one thing, the possibility of effectively harnessing them is another. In Nigeria,
it is apparently obvious that substrate availability is no constraint to biogas production but the problems
more or less lies in the possibility of harnessing these substrates so as to satisfy the demand of biogas
production (Akinbami et al., 1996). This section will thus look into the available substrates and their
potential uses for biogas production.
2.1
Domestic Waste
Domestic wastes vary from place to place depending on social and cultural practices as well as water
availability. However, based on available data, a rational estimate is made for average Nigerian family.
From (Winneberger, 1974), the total flow of waste-water from residential houses in the city of London is
put at 41.4 gallon per capital per day (gpcd) composed as shown in Table 3.
Table 3. Composition of waste water from residential houses
Source
Quantity (gpcd)
Kitchen sink
3.60
Bathtub
8.50
Bathroom sink
2.10
Laundry machine
7.40
Toilet
19.80
Total
41.40
Source: Winneberger, 1974
Based on the information, and assuming the same flow rate of domestic waster in Nigeria using the same
ratio of 3:2 persons per household (as used by Winneberger, 1974), the value for Nigeria (census
population count of 88.5 million in 1992) will be 1,144.969 million gpcd. This volume of waste should be
able to generate a reasonable amount of biogas. Considering Table 2, it can be estimated that such waste
volume will generate about 71.56 million m3 gas, since amount of gas generated is directly proportional to
the amount of volatile solids in the raw waste. The major constraint to achieving this is the inability to
collect these wastes. From all indications, only a minute fraction of the total domestic waste can be said
to be formally collected. In order to enhance the biogas technology, it therefore becomes important and
necessary to formulate and design processes for the collection of domestic wastes.
2.2
Livestock Waste
A 1992 livestock census carried out by the Federal Department of Livestock and Pest Control Services
gave the animal population in Nigeria with an average annual growth rate of 1.8% as shown in Table 4.
106
Table 4. Annual Population in Nigeria
Livestock
Population (million)
Poultry (indigenous)
102.8
Cattle
13.9
Goat
34.5
Sheep
22.1
Pig
3.4
Source: (Guardian Newspaper 11 March, 1992)
From Loehr (1984), average cattle will produce between 14 – 18 tons of feaces and manure per year, pigs
produce 6 - 8% of the body weight per day. In fact, volume of manure production can average about one
gallon per 100 lb animal per day. Assuming a waste production rate of 16 tonnes per animal, the total
amount of cattle manure that can be expected annually is (16 x 13.9m tonnes) which translates to 222.40
million tonnes. In the same manner, amounts of manure expected from poultry: (4×102.8 m tonnes),
411.20 million tons; pigs: (10 x 3.4m tonnes), 34.0 million tonnes; goat: (8 x 34.5 m tonnes), 276 million
tonnes; sheep: (8 x 22.1m tonnes), 176.80 million tonnes of manure respectively per annum. Hence the
total amount of livestock manure expected yearly is 1,120.4 million tonnes. From Table 2, for the cattle
manure (222.4 million tonnes) an equivalent volume of biogas is 20 million tonnes, for poultry, 411.2/
31.19 = 13.18 million tonnes; for goat, 276/28.95 = 9.53 million tonnes, for sheep, 176.8/28.95 = 6.11
million tonnes and for pigs 34/26.35 = 1.46 million tonnes of biogas respectively. The compositions of
different animal manures are summarized in Table 4.
Table 5: Estimated Biogas Production from Livestock Wastes in Nigeria
Livestock
Population
Annual manure production
(million)
(million tonnes)
Cattle
13.9
222.4
Poultry
102.8
411.2
Sheep
22.1
176.8
Pig
3.4
34
Goat
34.5
276
Total
2.3
Biogas
equivalent
(million tonnes)
20
13.18
6.11
1.46
9.53
50.28
Vegetable, Fruit and Wine Processing Waste
This is another viable option for generation of raw materials for biogas technology. A reasonable percent
of these vegetables and fruits come off as wastes in the processing industries and can be utilized for
biogas generation. As recorded from an analysis, Splitttstoesser and Downing (1969), Table 6 shows the
constituents of wastes from vegetable, fruit and wine processing.
Table 6: Waste characteristics from vegetables, fruit and wine processing
Product
COD (mg/litre)
BOD (mg/litre)
BOD/COD
(mean)
Beets
1,800 – 13,200
1,200 – 6,400
0.51
Beans, green
100 -2,200
40 – 1,360
0.55
Beans, wax
200 – 600
60 – 320
0.58
Carrots
1,750 – 2,900
800 – 1, 900
0.52
Corn
3,400 -10, 100
1,600 – 4,700
0.50
Peas
700 – 2,200
300 – 1,350
0.61
Sauerkrant
500 – 65,000
300 – 4,000
0.66
Tomatoes
650 – 2,300
450 – 1,600
0.72
Apples
400 – 37,000
240 – 19000
0.55
pH
5.6 -11.9
6.3 – 8.6
6.5 – 8.2
7.4 – 10.6
4.8 – 7.6
4.9 – 9.0
3.6 – 6.8
5.6 – 10.8
4.1-7.7
107
Cherries
1,200 – 3,800
660 – 1,900
Grape juice
550 – 3,250
530 – 1,700
Wine
50 – 12, 000
30 – 7,600
a
Source: Splittstoesser and Downing (1969)
b
minimum amount of wash and cooling waters
0.53
0.59
0.60
5.0 – 7.9
6.5 – 8.2
3.1 -9.2
in addition to these data, one often observes that enormous portion of annual fruit and vegetable
production goes to waste as a result of the lack of adequate storage and or/ preservative systems. In
essence, these deteriorated fruits and vegetables which are apparently no longer good enough for human
consumption can be utilized as raw materials for biogas technology. Although a statistical value is not
feasible at the moment, a conservative estimate shows a reasonable amount.
2.4
Brewery Effluent
This also offers an interesting approach towards generating raw materials for biogas technology. With an
estimated number of about one hundred and fifty breweries scattered all over the country, considering the
amount of effluents generated per brewery, it offers a viable source for raw material utilization for biogas
technology. From available information though not figurative, the total effluent generated by a brewery
per day can sustain a small scale biogas plant and adequately complement the energy requirements of
such brewery.
2.5
Other Substrates
A whole lot of other substrates sources are available in the country depending on locations. Food
processing factor such as milling industries (rice, maize and other grains), cassava and yam processing
wastes (peeling, wastewater and fibres, meat processing wastes, newspapers, independent grass amongst
others are all utilizable raw materials for biogas technology. Although there are alternative uses of these
wastes, a comparative evaluation of benefits as regards biogas generation and these other alternatives
shall provide a basis for a rational choice. The existence of these other alternatives reduces the amount
available for the technology. However, depending on the need of a particular locality, it may or may not
be viable sources. For instance, where wastes are used for animal feed preparations, better approach may
be to depend on the animal waste, indirectly or otherwise benefiting from the raw materials.
In summary, one can deduce the availability of substrates in Nigeria for biogas technology. A further step
will be in the direction of means of putting these wastes together for a sustainable supply. In the present
situation of uncoordinated availability the establishment of a biogas plant may not achieve its aim and
objectives. This condition further illustrates the idea of localization of the technology within suitable
areas or communities so as to ensure a continuous supply of raw materials.
3.
POTENTIAL USES AND BENEFITS OF BIOGAS AND BY-PRODUCTS IN NIGERIA
The gas produced by the anaerobic treatment of organic waste (biogas) is colourless, burnable, and
contains about 50 – 65% methane, 30 – 45% carbon dioxide and small percentage of hydrogen sulphide,
hydrogen, carbon monoxide and other gases (John 2010; Salminen and Rintala, 2002; Braun and
Wellinger, 2002). The exact composition of the gas is dependent on the nature of the substrate and the
operating conditions of the anaerobic unit. Anaerobic units often yield two products namely the biogas
itself and a semi-solid by-product called sludge or effluent.
3.1
Uses Of Biogas
The success of biogas production hinges on a sufficient demand, ability to store it, use it or convert it to
another form of energy. The most common uses of biogas include lighting, cooking, drying, water
pumping, grain milling and it can also be used to fuel internal combustion engines (Loehr, 1984;
108
Mattocks, 1984; Plöchl and Heiermann, 2006). With appropriate levels of skill and scale, biogas can be
pressurized and stored, cleansed for sale to commercial gas suppliers or converted to electricity and sold
to power grids to meet peak energy needs. While biogas is an excellent fuel, it does have a fairly low
energy value for its volume; about 500 – 600 KJ/m3 (Mattocks, 1984; John, 2010) and the pressure in the
distribution lines may be low. Lamps, stoves, refrigerators and other appliances require specially designed
Desks to offset the low energy value and low gas pressures.
A lot of contributions can come from biogas technology in solving much of Nigeria’s power needs
(Akinbami et al., 1996; Yusuf, et al., 2011). The stress being exerted on the forest reserves will be
reduced and availability of power and energy required in homes and farms will be guaranteed. The onfarm energy requirements of lighting, drying, heating, refrigeration can be adequately or at least to some
extent be taken care of by proper utilization of farm and allied wastes and by-products to produce biogas.
This can reduce the ultimate expenses on the farm for the biogas generation. In the same way, the biogas
production can be an integral part of large or small scale factories or industries where the processing
wastes (such as meat, fish or vegetable processing wastes) can be appropriately utilized and converted to
biogas.
3.2
Uses of Biogas Sludge
The residue left in the digester at the end of the digestion period is called the sludge and it consists of
lignin, lipids, synthesized microbial cells, volatile acids and other soluble compounds, inert materials in
the original waste and water. Anaerobic treatment conserves nutrients for the production of crops and
practically all nitrogen present in the raw waste entering the anaerobic unit is conserved (Loehr, 1984).
Key by-products of anaerobic digestion include digested solids and liquids, the most common use of
anaerobically treated material is as a fertilizer and soil conditioner (Buendía, et al., 2009; John, 2010;
Salminen and Rintala, 2002).
The anaerobic fermentation of waste of biogas production does not reduce its value as a fertilizer
supplement, as available nitrogen and other substances remain in the treated sludge (Alvarez and Lide, et
al., 2008; Fiorese, et al., 2008; Budiyono, et al., 2010; John, 2010; Salminen and Rintala, 2002; Braun and
Wellinger, 2002; Molinuevo, et al., 2009). The availability of this sludge will go a long way to alleviate
the problems of fertilizer scarcity prevalent in the country. Also most of the pathogens are destroyed in
the process of anaerobic digestion (FAO, 1996; Molinuevo, et al., 2009; Shih, 1993).
An advantage over raw manure is the improvement in the handling. By virtue of undergoing anaerobic
digestion, the sludge becomes less smelly and more easily handled. In fact, biogas production can
enhance integrated agro-activities in the sense that the agricultural products (crops or livestock) are
processed on the farm with biogas from their waste, and the future ones nurtured with the sludge from the
biogas generation. In addition to being used as fertilizer, the sludge can be added to animal feeds,
normally not exceeding 10% of the content. This will also be of importance in reducing the problems of
animal feed supplies. Where appropriate, the digested sludge can be added to fish ponds to support the
growth of plankton on which the fish feed.
3.3
Socio-Economic Benefits
The socio-economic implications of biogas technology need not be over emphasized. In addition to the
above mentioned benefits, biogas technology is a system of converting an otherwise costly waste into
beneficial products. This is envisaged to improve and enhance the overall well being of the rural
population who then have the ability to generate power and energy from their waste, improve their
agricultural output and ultimately contribute to their collective and individual economic base.
109
3.4
Environmental Benefits
Human waste
Meat, milk, eggs
Biogas fuel
The prominent environmental implication of biogas technology is the reduction in pollution of the
environment. By proper utilization of these wastes, a good number of pollutants are removed from the
environment thereby enhancing good health of the communities. From aesthetic view point, the removal
and utilization of wastes will leave the environment in a more beautiful condition by making the whole
place neat and possibly odourless. In addition, the system is capable of reducing the population of flies,
rodents, mosquitoes and other disease-carrying animals and micro-organisms, and thus minimizes their
consequent activities. In summary, biogas technology can be incorporated in an integrated management
system as can be seen from Figure 1 (Loehr, 1984).
Animals; pigs, chicken cows
Digester residue (N, P, K)
Crops (grass, forage, grain
Agricultural lands
Fig 1: Integration of crop residue, manure, and other wastes in biomass energy and utilization cycle
(Loehr, 1984)
4.
CONSTRAINTS TO THE APPLICATION OF BIOGAS TECHNOLOGY IN NIGERIA
Despite the obvious attractive benefits of biogas technology in Nigeria, there are certain fundamental
constrains to its complete adoption as a viable alternative to fuel and energy supplies. These constrains
are discussed in the following sections.
4.1
Dearth of Substrates
Although from available data, one observes a reasonable volume of substrate availability in Nigeria.
Despite this promising situation, a major consideration is the recoverability of these substrates for the aim
of biogas generation. The poor and uncoordinated system of waste disposal prevalent in the country
makes the collection of these substrates (waste) an uphill if not impossible task. To this effect, a lot of
otherwise viable substrates are not taken into consideration in the sitting of biogas technology, thereby
making the whole efforts to be futile.
110
4.2
Availability of Alternative Energy Sources
Another major constrains to the adoption of biogas technology in Nigeria is the availability of alternative
and more accessible energy and fuel sources. These alternative energy and fuel sources include petroleum
and allied products, gas, wood, electricity amongst others. These alternative sources though often quite
expensive are directly accessible to the people and often come in much neater and useable forms. Hence,
they exercise some reasonable advantage over biogas generation.
4.3
Lack of Technical Know-How
The lack of knowledge regarding the biogas technology is another important constrain to the adoption of
the technology in Nigeria. Adequate studies have not yet been undertaken in Nigeria with respect to
promoting the biogas technology. This unfortunate situation is not unconnected with the constraints listed
above as well as the social constraints. Biogas generation must be acceptable and learned a process
dependent on motivated, knowledgeable extension of the successful applications of the technology.
4.4
Social Aspect
Certain cultural and social factors hinder the adoption of biogas technology in Nigeria. In some places, it
is a taboo to handle wastes in such manner. Of prominent recognition also is the existing practice of the
people. Most often, those who handle wastes are relegated to the least step of the societal ladder and such
psychological perception is a constraint to adoption of biogas technology in rural areas.
4.5
Cost of Substrates
Based on the above listed constraints, the cost of recovering and collecting these substrates may negate
the aim and objective of developing a cheap energy source via biogas generation. A situation where the
cost of collection and handling of these substrates outstrips the equivalent economic benefits of the
technology, it will be foolhardy to go ahead in developing and adopting biogas technology.
5.
WAY FORWARD
We have shown in this paper that Biogas production from agricultural waste has very good potentials in
Nigeria as an alternative source of energy while a the same time assisting in converting waste to wealth,
and ensuring environmental sustainability. However, even with the potentials, the technology is not yet
well utilized in Nigeria due to some constraints discussed in the paper. In order to overcome these
constraints and develop the biogas business in Nigeria the following strategies are recommended:
i.
ii.
iii.
iv.
v.
vi.
vii.
Commissioning of more studies on all aspects of biogas production including quantification of
possible sources of substitutes, technology production, adoption and adaptation and safety issues
in biogas production.
Monitoring of awareness campaigns by government agencies, non-governmental organizations
and professional bodies.
Formation of a central stakeholder group to be made up of Researchers, business people,
marketers, producers, etc. The Forum can be call Biogas Association of Nigeria.
Production and installation of pilot plants in various locations to popularize the technology.
Hosting of more seminars and workshops at the rural level to sensitized potential users of the
technology.
Creation of a Special Fund for Biogas to encourage people who are interested in producing the
technology and those who want to adopt the technology.
Development of a robust policy on biogas.
111
6.
CONCLUSION AND RECOMMENDATIONS
Having discussed biogas potentials and viability in Nigeria, biogas uses and benefits as well as the
associated constraints in Nigeria, it is hoped that this work within its scope has tried to bring biogas
technology nearer to the people. Biogas technology is indeed very necessary at this crucial stage when oil
prices are fast escaping the range of the common man. In the same way, the much talked about
environmental pollution will be minimized and reduced by proper utilization of wastes. Socio-economic
status of people will also turn for better by the conversion of otherwise costly waste to cheap energy
source.
Biogas generation must be acceptable to the people and understood as a process dependent on motivated,
knowledgeable extension agents or others who can point to successful application of the technology
and/or are able to demonstrate it effectively. To this end, extensive studies and evaluation of the
technology have to be carried out so that much of the constraints associated with its adoption can be
overcome and much of the benefits realized. It is in this light that the technology is being advocated as a
viable alternative to power and energy source especially with the current conditions associated with other
forms of power and energy sources.
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113
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change without notice.
Submission of Manuscript: Submission of an article for publication implies that it has not been
previously published and is not being considered for publication elsewhere. Four copies of the
manuscript and N1000 processing fee should be sent to:
115
The Editor-In-Chief
Journal of Agricultural Engineering and Technology (JAET)
C/o The Editorial Office
National Centre for Agricultural Mechanization (NCAM)
P.M.B. 1525, Ilorin, Kwara State
Nigeria.
Papers can also be submitted electronically to any member of the Editorial Board and to the Technical
Assistant to the Editor In Chief at ifeeolife@yahoo.com.
116

Volume 19 (No. 1) - Nigerian Institution of Agricultural Engineers

Transcription

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