Document

Proceedings of The Inter-Disciplinary Academic Conference on Uncommon Development Vol. 4 No.2 January, 15-16
2015 – University of Jos Multi-purpose Hall, Main Campus, Jos, Plateau State
www.hummingpub.com
ASSESSMENT OF FRICTIONAL AND THERMAL PROPERTIES OF BAOBAB SEEDS
(ADANSONIA DIGITATA)
Adamu A.M., Sheriff B.G., Dauda A., Goni M.M. and Kachalla B.G.
“Department Agricultural Engineering
Ramat Polytechnic, Maiduguri”
Abstract
To determine the frictional and thermal properties of Baobab seeds, four moisture levels were
created determined by soaking the sample in water and were collected after 30 minutes intervals.
The samples were then dried under natural air for about five hours. The various moisture levels
were preserved in the polythene bags and stored in a refrigerator at 5 0c to keep them stable and
prevent moisture loss. The long period of smoking is because when initial trials were carried for
lesser hours, it yields low range of moisture content. The initial moisture content of Baobab
(Adansonia digitata) seed was found to be 20.7% (dry basis). The three other moisture levels
obtained after conditioning the seeds were 38.4%, 50.3% and 63.8% (dry basis) respectively.
These investigations were carried out at above moisture content levels to determine the effects of
moisture content on the frictional and thermal properties of Baobab (Adansonia digitata) seeds.
The study revealed that the specific heat increased with increase in moisture content. Similar
observation was made for sheanut kernel, and cumin seeds (Aviara et al, 2008) but with some
variation that occur due to differences of seeds, hardness and strength.
Keywords: Baobab seeds, Frictional, Moisture and Thermal properties,
1.0 Introduction
General Background
Baobab (Adansonia digitata) is a tree native to certain tropical regions in Africa, belonging to
Bombacaceae family; (Boshch et at 2004; Jansen et al 1991); which grows on countries around
the African countries including south Africa, Botswana and Mozambique. Baobab tree produces
fruits with a powdery pulp found to contain high amount of vitamin C often consumed as food or
added to b rcbeverages, baobab fruits sometimes used for medicinal purposes (Nkafamiya et al,
2007; Belewu et al., 2008).
Baobab is a massive deciduous fruits tree, up to 20-30m high, with a life span of several
hundred years. It’s swallow and often hollow trunk like a huge bottle and can be as broad as 3.7m
in diameter. It bears short, stout and tortuous branches and has a thin canopy. Baobab is strong
anchored in the soil by an extensive and strongly roots system that grows 2m deep and whose
diameter may be higher than the tree height. The ,leaves are simple or digitally compound, dark
green on top, and borne at the end of a 16cm-long petiole. The lengths are between 5-15cm long
and 1-57cm broad. Baobab shed its leaves during early dry season and new leaves appear after
flowering. The pentamerous flowers are white, large (20cm in diameter and 25cm long), and hang
from stalks on pedicels up to 90cm long. The fruits are voluminous (35cm long and 17cm in
diameter) ovoid capsule with a hard woody envelope containing a pulp and black seeds. Once
ripe, the fruits envelope becomes brittle and the pulp takes on a chalky consistency. The tree
starts producing fruits after 30 years (Ecocorp, 2011; FAO, 2011; Orwa et al., 2009; Bosch et al.,
2004., Jansen et al., 1991).
Baobab is mainly used for food. The fruits, flowers shoots, roots of seedlings and even
the tree roots are edible. The leaves can be either fresh, as a cooked vegetable, or dried and
powered as a functional ingredient (thickener) of soups and sauces. The flowers, shoots and roots
of seedlings are eaten (Bosch et al., 2004). The fruits called monkey-bread, contains a white,
Proceedings of The Inter-Disciplinary Academic Conference on Uncommon Development Vol. 4 No.2 January, 15-16
2015 – University of Jos Multi-purpose Hall, Main Campus, Jos, Plateau State
www.hummingpub.com
nearly, acidic testing nutritious flesh that can be eaten as sweet, used to make a refreshing drinks
and the creams, or used to adulterated and curdle milk. The seeds yield edible and pleasant testing
oil, and the oil extraction result in an oil meal. The bark is used as fibre or as firewood. The roots,
that are boiled and eaten in times of famine, contain tannins that provide a useful red dye (Orwa
et al., 2009). In the Sahel, black bark and red back are mainly used as leaf vegetables and grey
bark types are used for fibre. (Bosch et al., 2004). Burning baobab fruits pulp produces an acrid
smoke used to deter insects troublesome to live stock (Orwa et al., 2009). Optimal growth
conditions are average day temperature ranging from 190c 350C, annual rainfall between 300500mm and fertile slightly acidic, sandy topsoil overlaying loamy subsoil. However the African
baobab may withstand mud lower and more irregular rainfall conditions (90-1500mm) and grown
on a poorly drained soil with a heavy texture, though not on deep sands probably due to lack of
anchorage (Orwa et al., 2009; Bosch et al; 2004).
The Baobab seeds contain high concentrations of oxalates (10%), phytate (2%) and
spannins (3-7%) (Nkafamiya et al., 2007) Belewu et al., 2008). Trypsin inhibitors have also been
found (5.7 T i u/mg; Osman 2004) but can be reduced by 83% by alkali treatment (Bosch et al.,
2004). Whole seeds contain amylase inhibitors and tannins (Igboeli et al., 1979; Osman, 2004).
No tannins or condensed tannins were found in the dehullic seeds (Belewu et al., 2008). Roasting,
hot water, hot alkali, and acid treatment significantly reduces the tannins content while roasting
dehulling, cold water and hot alkali treatment also reduces amylase inhibitors activities (Igboeli et
al., 1979).
The nutritive value of Baobab oil meal depends on the process. The dry matter contains
17-30% crude protein, 15-25 of crude fibre, and 5-14% residual oil (Mudzimare et al; 2011;
feedipedia, 2013). The importance of the Baobab oil includes, since it is fixed oil its will not
burn the skin when used neat on the skin, but since it is such as rich and nourishing oil it can be
included in far smaller quantities into another carries oil or base. The pure oil extracted from
seeds and the oil is easily and quickly absorb by the skin leaving no oiliness or greasiness.
Baobab seed oil is highly moisturizing, emollient and smoking which is partly due to the
ingredient found in the oil, it contain vitamin A,B,E and F vitamin A and F (which are polylin
saturated fatty acid) are actively involved in the rejuvenation and renewal of cell membrane,
while vitamin E is a superior antioxidant, which help to fight aging. (Igbochi et al; 1979, Osman
2004).
In traditional African medicine, Baobab seeds are used to treat number of illnesses
(including asthma, fever, diarrhea, malaria and smallpox). In addition, practitioners of traditional
African medicine, the seeds often used to curb inflammation (Belewu et al; 2008).
2.1
Static coefficient of friction
Static coefficient of friction is the coefficient of friction values measured as two surfaces just
begin to move against each other. Kit is the ratio of the maximum possible friction force parallel
to the surface of contact which acts to prevent two bodies in contact and at rest with respect to
each other from sliding to moving over each other, to the force normal to the surface of contact
with which the bodies press against each other. Before granular materials can flow from a bin by
gravity or a loaded auger can be started by a power source, the forces of static friction must be
overcome. Static coefficient of friction is essential in the design of handling equipment.
The static coefficient of friction of grains and seeds has been determined by various
investigations using the inclined plane method. The investigations have shown that coefficient of
friction increased with moisture content and varied with the surface on which the seed slides.
Proceedings of The Inter-Disciplinary Academic Conference on Uncommon Development Vol. 4 No.2 January, 15-16
2015 – University of Jos Multi-purpose Hall, Main Campus, Jos, Plateau State
www.hummingpub.com
Singh and Goswani (1996) investigated the effects of moisture content of Gumin seeds on its
static coefficient of function using the filling of an inclined plane method and found that the static
coefficient of function measured nearly with respect to moisture content for all four surfaces,
namely stainless steel, aluminum, galvanized and mild steel referred the least friction.
The static coefficient for African nut meg (monodoramyristica) was determined by
Burnbai et al (2007) at moisture level of 4.93% dry basis. Values obtained revealed that the
coefficient of static friction using steel galvanized iron, plywood and rubber surfaces were 0.354,
0.502, 0.633 and 0.702 respectively.
This trend indicates that the rubber has the highest coefficient of static friction and
galvanized iron is least. Static coefficient of friction of jatropha seed increased linearly against
the surface of these structural materials namely; plywood (44.12%), mud content increase from
4.75-19.56% dry basis. Static coefficient of corn seeds on three surfaces (plywood compressed
plastic and galvanized iron) against moisture content in the range of 5.15 to 22% dry basis. It was
observed that the static coefficient of friction increases with increase in moisture content for all
the surface (Tarighi et al; 2011).
The maximum value of 0.67 was obtained on the surfaces of compressed plastic and
minimum value of 0.57 was on the surfaces of the galvanized steel. Similar findings were
reported for pumpkin seeds (Josh, et al; 1993); Karingda seeds (Sulthar and das 1996), millet
(Baryeh 2002); okro seeds (sahoo and srivastava 2002).
2.2
Kinetic Coefficient of friction
The method of moving the material against a surface used in determining the kinetic
coefficient of friction involves the placing of a top less and bottom less box on a structural
surfaces and filling it with seeds sample. The box is connected by a string parallel to the surface
of the material and passed on a pulley to a pan hanging to a string. The weights are placed in the
pan until the box moved uniformly when given a gentle push. The kinetic coefficient of friction
of seeds using different surfaces was determined by (Aviara et al; 2010) using the surfaces like
plywood, glass, galvanized iron steel and bagio bag.
2.3
Thermal Properties:
The Thermal Properties are heat dependent properties. Their importance in agricultural
processing is very large. During food processing most farm products undergo heat treatment
either in form of cooling, cooking, drying etc. in all these processes, heat is either added or
removed from the material. The efficiency of any of the process will depend to a large extent on
Thermal characteristics of the material involved.
Thermal Properties of agricultural materials can be defined as those characteristics and
qualities of agricultural materials that are sensitive or liable to heat processing and form important
in the design of equipment and prediction of processes. Heating and cooling of agricultural
products may be accomplished by method of convection, conduction and radiation. Knowledge of
such thermal characteristics as specific, thermal conductivity, thermal diffusivity, surface
conductance and emissivity as well as physical, characteristics as density, shape, and size is
essential for design. A heat balance for heating or cooling system cannot attempt without the
knowledge of heat capacity of the materials. The heat treatment of biological material, time and
temperature are equally important of viability, nutrients and quality of the materials that are to be
preserved.
Proceedings of The Inter-Disciplinary Academic Conference on Uncommon Development Vol. 4 No.2 January, 15-16
2015 – University of Jos Multi-purpose Hall, Main Campus, Jos, Plateau State
www.hummingpub.com
Thermal Properties play an important role in the analysis of food processing operations.
Numerous food processing unit operate are heat or energy sensitive. Heat exchanged and
resulting temperature- pressure must consider the minimization of reactions browning, oxidation
–reduction in order to preserve the acceptability and nutritional value of the food. Thermal
Properties are also useful when evaluating capacities of dying system, studying aid of
mathematical and numerical dying models. Enthalpy and specific heat are required to calculate
the heat local in food processing operations (Barbosa Canovas, 2006).
Knowledge of such properties as specific heat, Thermal conductivity, Thermal
diffusively, surface conductance and emissivity is important for the design equipment like
heating, cooking, freezing. It required in estimation of the amount of energy required to change
the temperature of products (Mohsenin 1986).
Thermal Properties of various products have been studied by researchers such as
Kazarian and Hall (1965), Suter et al (1995), Shephard and Bhardwaj (1986) and Dutta et al.
(1988).
Singh and Goswani (1990) using the differential scanning calorimeter measured the
specific heat increased from 1330-3690 J/kgk with increase in temperature from 70-150 and
moisture content from 1.8% to 25% dry basis. The specific heat displayed second order
polynomial relations with temperature and moisture content.
3.0
Material and Methods
The study carried out in the Agricultural and Environmental Resources Engineering University of
Maiduguri, Nigeria. Maiduguri is located at 13005E and 11005E and 345m above mean sea level
with the mean annual rainfall of about 625mm and annual temperature of 28 - 320C.
3.1 Experimental procedure
The seeds were soaked in water with detergent and washed thoroughly in over flowing
tap water. Foreign matter, broken and immature seeds were removed. The clean seeds were dried
at room temperature of 310C for 12 days and the seeds were stored in an air tight polythene bags.
Among these four moisture level were created. first moisture level were taken at market
moisture level, others were determined by soaking the sample in water and each moisture was
collected after 30 minutes, 1 hour and 1 hour 30 minutes respectively, followed by spreading out
in this layer to dry in natural air for about five hours. The various moisture levels were preserved
in the polythene bags and stored in a refrigerator at 50c to keep them stable and prevent moisture
loss. The long period of smoking is because when initial trials were carried for lesser hours, it
yields low range of moisture content.
Measurement were replicated four times for each moisture content with different
samples, the relationship found to be existing with moisture content and temperature is expressed
using regression equations. Also the variation with moisture content and temperature is plotted.
Kinetic coefficient of friction was measured and evaluated for fire structural surfaces
namely: Hessian bag materials, fiber glass, and galvanized steel, plywood parallel to the direction
of movement and to the perpendicular to the direction of movement.
Proceedings of The Inter-Disciplinary Academic Conference on Uncommon Development Vol. 4 No.2 January, 15-16
2015 – University of Jos Multi-purpose Hall, Main Campus, Jos, Plateau State
www.hummingpub.com
Measurements were replicated four times for each moisture contents with different
samples. The relationship found to be existing with moisture content is expressed using equation.
Also the variation with moisture content is plotted.
Plate 1: Baobab (Adansonia digitata) seeds.
Proceedings of The Inter-Disciplinary Academic Conference on Uncommon Development Vol. 4 No.2 January, 15-16
2015 – University of Jos Multi-purpose Hall, Main Campus, Jos, Plateau State
4.0
Results and Discussions
4.1
Seed Moisture Content
www.hummingpub.com
The initial moisture content of Baobab (Adansonia digitata) seed was found to be 20.7%
(dry basis). The three other moisture levels obtained after conditioning the seeds were 38.4%,
50.3% and 63.8% (dry basis) respectively. These investigations were carried out at above
moisture content levels to determine the effects of moisture content on the frictional and thermal
properties of Baobab (Adansonia digitata) seeds. Those were: Kinetic coefficient of friction,
static coefficient of friction, specific capacity and coefficient of restitution.
4.2
Specific Heat
The specific heat of Baobab (Adansonia digitata) seeds at four moisture levels in the
range of 20.7 to 63.8% (dry basis) and temperature (1000c) between the initial temperature of
seeds and final temperature of water and seed mixture was found to lie between 1530J/kgk 2236.9J/kgk it was discovered that the specific heat increased with increase in moisture content.
Similar observation was made for sheanut kernel, and cumin seeds (Aviara and Haque, 2001,
Aviara et al, 2008, Despande and Bal, 1999). But with some variation that occur due to
differences of seeds, hardness and strength. Thermal properties of seed are essential for
determining the equipment and processes needed for the seeds to maintain its temperature without
boiling or germinating.
Table 1: Specific heat capacity
S/N
SPECIFIC HEAT(J/kgK)
M.C (% d.b)
1
1530
20.7
2
1968.4
38.4
3
2050
50.3
4
2236.9
63.8
Proceedings of The Inter-Disciplinary Academic Conference on Uncommon Development Vol. 4 No.2 January, 15-16
2015 – University of Jos Multi-purpose Hall, Main Campus, Jos, Plateau State
www.hummingpub.com
specific heat against moisture content
specific heat capacity(J/KgK)
2400
2200
y = 15.919x + 1257
R² = 0.9459
2000
1800
1600
1400
1200
0
10
20
30
40
50
60
70
M.C (% d.b)
Figure 1: Effect of moisture content on Specific heat capacity of the seed
4.3
Kinetic Coefficient Friction
The Kinetic coefficient friction increase as the moisture content varied on different
surfaces, on mica surface the Kinetic coefficient friction increases from 0.163 to 0.195, for the
fibre glass 0.159-0.208 respectively. Similar head was reported for sheanut kernel, guna seed and
kernel and Gumin seeds (Aviara and Haque, 2001, Aviara et al; 2008). Kinetic coefficient also
varies with seeds characteristics.
Table 2: Kinetic coefficient of friction
S/N
M.C % d.b
mica surface
fibre glass
hessian bag
plywood
1
20.7
0.163
0.159
0.245
0.203
2
38.4
0.196
0.165
0.247
0.206
3
50.3
0.188
0.169
0.253
0.202
4
63.8
0.195
0.163
0.251
0.208
Proceedings of The Inter-Disciplinary Academic Conference on Uncommon Development Vol. 4 No.2 January, 15-16
2015 – University of Jos Multi-purpose Hall, Main Campus, Jos, Plateau State
www.hummingpub.com
kinetic coefficient of friction against M.C
kinetic coefficient of friction
0.3
mica surface
fibre glass
hessian bag
y = 0.0002x + 0.2417
R² = 0.7129
0.25
y = 8E-05x + 0.2013
R² = 0.2858
0.2
y = 0.0007x + 0.1566
R² = 0.6258
y = 0.0001x + 0.1587
R² = 0.2879
0.15
0.1
10
20
30
40
50
60
70
M.C (% d.b)
Figure 2: Effect of moisture content on the Kinetic coefficient of friction of the seeds
4.4
Coefficient of Restitution
The coefficient of restitution of baobab (Adansinia digitata) seeds at four moisture levels
in the range of 20.7 to 63.8% (dry basis) was determined at different height between 150cm,
100cm and 50cm respectively. It was observed that the coefficient of restitution decreases with
increase in moisture content. This is due to the weight obtained and as water charge the nature of
seeds, so the rebonce is decreasing with increase in moisture content.
For 150cm height, the coefficient restitution decrease from 0.447-0.408 on Mica surface,
0.365-0.305 on fibre glass and 0.34y6-0.283 on plywood. For 100cm height, the coefficient of
restitution decreases from 0.458-0.316 on Mica surface, 0.387-0.3 on fibre glass and 0.316-0.223
on plywood respectively. For 50cm height, the coefficient of restitution decrease from 0.4690.316 mica 0.447-0.245 and 6.346-02 an plywood. Similar was reported by (Adams, 2002),
sphere ball electroplastic (Aviara et al 2009) for cumin seeds.
Proceedings of The Inter-Disciplinary Academic Conference on Uncommon Development Vol. 4 No.2 January, 15-16
2015 – University of Jos Multi-purpose Hall, Main Campus, Jos, Plateau State
www.hummingpub.com
Table 3: Coefficient of Restitution at 150cm
S/N
M.C % d.b
Mica
Fibre glass
Plywood
1
20.7
0.447
0.365
0.346
2
38.4
0.432
0.356
0.316
3
50.3
0.424
0.336
0.306
4
63.8
0.408
0.305
0.283
coefficient of restitution against M.C at 1 50cm
mica
coefficient of restitution
0.5
fibre glass
ply wood
y = -0.0009x + 0.466
R² = 0.9885
0.45
0.4
y = -0.0014x + 0.4004
R² = 0.9059
0.35
y = -0.0014x + 0.3742
R² = 0.9875
0.3
0.25
10
25
40
55
M.C (% d.b)
Figure 3: Effect of moisture content on the Coefficient of Restitution at 150cm
70