Midterm Exam Spring2015 Solutions

QUESTION
MARKS
Q-1
Q-2
EASTERN MEDITERRANEAN UNIVERSITY
FACULTY OF ENGINEERING
DEPARTMENT OF MECHANICAL ENGINEERING
MENG 244 THERMODYNAMICS
MID-TERM EXAM
(Spring 2014-2015)
STUDENT’S
Q-3
Q-4
Q5
TOTAL:
(Out of 25)
NAME, SURNAME:………………………………….
NUMBER
:………………………………….
GROUP NO
:……….
Type of examination: B.S. Examination – Mid Term
Time allowed: 90 mins
Date: April 24, 2015
Instructions to candidates
1. This is a closed book exam.
2. Do not ask any questions to the invigilators.
3. Answers are expected to all questions.
4. Answers are to be written in the spaces provided under each question.
5. Only non-programmable calculators are allowed.
6. Be clear and specific and give units to answers.
7. Give explanatory notes where necessary.
8. The exam contains total of 7 pages.
1
Question 1:
Define the following terms in the spaces provided. (5 marks)
a) Closed and open system:
c) First Law of Thermodynamics:
d) Second Law of Thermodynamics:
e) Kelvin-Plank Statement:
f) Clasius Statement:
2
Question 2:
Complete the following table for R-134a. You MUST show all your work. Just filling
the table will not get you any marks. Show all the steps. (5 marks)
T (oC)
-12
P (kPa)
320
30
Phase Description
0.0065
550
60
v (m3/kg)
Saturated vapor
600
3
Question 3:
A piston-cylinder device initially contains 1.4-kg saturated liquid water at 200°C. Now
heat is transferred to the water until the volume quadruples and the cylinder contains
saturated vapor only. Determine (a) the volume of the tank, (b) the final temperature
and pressure, and (c) the internal energy change of the water. (5 marks).
4
Question 4:
Air at 100 kPa and 280 K is compressed steadily to 600 kPa and 400 K. The mass
flow rate of the air is 0.02 kg/s, and a heat loss of 16 kJ/kg occurs during the
process. Assuming the changes in kinetic and potential energies are negligible,
determine the necessary power input to the compressor. (5 marks).
5
Question 5:
A heat pump is to be used to heat a house during the winter. The house is to be
maintained at 21°C at all times. The house is estimated to be losing heat at a rate of
135,000 kJ/h when the outside temperature drops to -5°C. Determine the minimum
power required to drive this heat pump. (5 marks).
6
Formula:
y = yf + xyfg
h = u + Pv
𝐷𝑒𝑠𝑖𝑟𝑒𝑑 𝑂𝑢𝑡𝑝𝑢𝑡
𝜂𝑡ℎ = 𝑅𝑒𝑞𝑢𝑖𝑟𝑒𝑑 𝐼𝑛𝑝𝑢𝑡
7