A 22 kw refrigerator or heat pump operates between 17

A 2.2 kW refrigerator or heat pump operates between – 17
o
C and 38
o
C. Determine the maximum theoretical heat that can be transferred from the
cold reservoir.
a) 10.24 kW b) 12.44 kW c) 14.01 kW d) 14.24 kW
Solution:
L H
L L
T T
T
W
Q
−
=
( )
kW 24 . 10
17 38
17 273
2 . 2
T T
T
W Q
L H
H
H
=
⎟
⎠
⎞
⎜
⎝
⎛
+
−
=
⎟
⎟
⎠
⎞
⎜
⎜
⎝
⎛
−
=
2. Determine the final volume of the isentropic compression of 1 m
3
air from 20 kPaa to a pressure of 100 kPaa.
a) 1.9047 m
3
b) 0.5253 m
3
c) 0.3168 m
3
d) 0.1061 m
3
Solution:
( )
3
4 . 1
1
3
k
1
2
1
1 2
m 3168 . 0
100
20
m 1
p
p
V V = ⎟
⎠
⎞
⎜
⎝
⎛
=
⎟
⎟
⎠
⎞
⎜
⎜
⎝
⎛
=
3. What is the clearance of an ideal Otto engine if the efficiency is 40 % and k = 1.3?
a) 21.18 % b) 12.27 % c) 22.28 % d) 23.28 %
Solution:
489 . 5
40 . 0 1
1
e 1
1
r
3 . 0
1
1 k
1
k
=
⎟
⎠
⎞
⎜
⎝
⎛
−
=
⎟
⎠
⎞
⎜
⎝
⎛
−
=
− ( ) ( )
% 28 . 22 % 100
1 489 . 5
1
% 100
1 r
1
c
k
=
⎟
⎠
⎞
⎜
⎝
⎛
−
=
⎟
⎟
⎠
⎞
⎜
⎜
⎝
⎛
−
=
4. A 500 Hp internal combustion engine has a brake mean effective pressure of 551.5 kPa at full load. What is the friction power if the mechanical
efficiency is 85 %?
a) 75 Hp b) 88.24 Hp c) 78.24 Hp d) 98.24 Hp
Solution:
Hp 24 . 88 500
85 . 0
500
BP
BP
BP IP FP
m
= − ⎟
⎠
⎞
⎜
⎝
⎛
= −
⎟
⎟
⎠
⎞
⎜
⎜
⎝
⎛
η
= − =
5. A fiber glass insulating board with thermal conductivity of 0.05 W/m-
o
C is to be used to limit the heat losses to 100 W/m
2
for a temperature
difference of 150
o
C across the board. Determine the thickness of the insulating board.
a) 57 mm b) 65 mm c) 56 mm d) 75 mm
Solution:
( )
( )( )
mm 75 m 075 . 0
m / W 100
C 150 C m / W 05 . 0
A
q
T k
x
2
o o
k
= =
⋅
=
⎟
⎟
⎠
⎞
⎜
⎜
⎝
⎛
∆
=
6. A Brayton cycle has a compression ratio of 11. Find the cycle thermal efficiency if the compression and expansion exponent is 1.25.
a) 62.99 % b) 45.09 % c) 49.05 % d) 69.22 %
Solution:
( )
( )
( )
( )
( )
( )
% 09 . 45 % 100
11
1
1 % 100
r
1
1 % 100
r
1
1 e
25 . 0 1 n
k
k
1 n
p
the
=
⎥
⎥
⎦
⎤
⎢
⎢
⎣
⎡
− =
⎥
⎥
⎦
⎤
⎢
⎢
⎣
⎡
− =
⎥
⎥
⎥
⎦
⎤
⎢
⎢
⎢
⎣
⎡
− =
− −
7. An air standard Otto cycle has a compression ratio of 10. The initial temperature is 30
o
C and initial pressure is 100 kPaa. If heat added is 1150
kJ/kg, find the mean effective pressure.
a) 884.3 kPa b) 848.3 kPa c) 488.3 kPa d) 838.4 kPa
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JCSF Engineering Review Center IPD PPD General Examination
2
Solution:
( )
( )
( )
( )
% 2 . 60 % 100
10
1
1 % 100
r
1
1 e
4 . 0 1 k
k
th
=
⎥
⎥
⎦
⎤
⎢
⎢
⎣
⎡
− =
⎥
⎥
⎦
⎤
⎢
⎢
⎣
⎡
− =
−
( ) ( )( )
kg / kJ 3 . 692 150 1 602 . 0 q e w
A th
= = =
( )( )
kg / m 8699 . 0
100
273 30 28708 . 0
p
RT
v
3
1
=
+
= = kg / m 08699 . 0
10
8699 . 0
r
v
v
3
k
1
2
= = =
kPa 3 . 884
08699 . 0 8699 . 0
3 . 692
v v
w
v
w
p
2 1 D
m
=
−
=
−
= =
8. A heater has an average temperature of coil is 80
o
C. Air enters at 29
o
C and leaves at 65
o
C. Find the by-pass factor.
a) 0.50 b) 0.3191 c) 0.2941 d) 0.7059
Solution:
2941 . 0
29 80
65 80
BPF =
−
−
=
9. For an electric generator running at 15 revolution per second and 60 Hz, find the number of poles.
a) 16 poles b) 10 poles c) 12 poles d) 8 poles
Solution:
( )
( )
poles 8
60 15
60 120
N
f 120
p = = =
10. A feed having 18 % moisture delivers 9000 kg/hr of dried product having 97 % solid. Find the moisture removed.
a) 1646.34 kg/hr b) 1466.34 kg/hr c) 1664.34 kg/hr d) 1436.46 kg/hr
Solution:
( ) ( )
2 2 1 1
MC 1 m MC 1 m − = −
( ) ( )
hr / kg 34 . 646 10
18 . 0 1
03 . 0 1 9000
MC 1
MC 1 m
m
1
2 2
1
=
−
−
=
−
−
=
hr / kg 34 . 1646 000 9 334 . 646 10 m m m
2 1
= − = − = ∆
11. A thermal power plant generates 9000 kW and has also 400 kW power needed for auxiliaries. If heat generated by fuel is 15500 kW, what is the net
thermal efficiency in%?