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GATE Mechanical Engineering (ME) 2020 Shift 1 Solved Paper
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© examsnet.com
Question : 63
Total: 65
Air (ideal gas) enters a perfectly insulated compressor at a temperature of 310 K.The pressure ratio of the compressor is 6. Specific heat at constant pressure for air is 1005 J\/kg.K and ratio of specific heats at constant pressure and constant volume is 1.4. Assume that specific heats of air are constant. If the isentropic efficiency of the compressor is 85 per cent, the difference in enthalpies of air between the exit and the inlet of the compressor is ______ kJ/kg (round off to nearest integer).
Your Answer:
Validate
Solution:
Temperature at inlet of compressor
(
T
1
)
=
310
k
For above (T-S) diagram of Brayton cycle
Isentropic efficiency
(
η
isen
)
=
0.85
=
Isentropic work
Actual work
0.85
=
h
2
−
h
1
h
2
′
−
h
1
h
2
′
−
h
1
=
h
2
−
h
1
0.85
=
C
p
(
T
2
−
T
1
)
0.85
Now for
(
1
−
2
)
isentropic process
=
T
2
T
1
=
(
P
2
P
1
)
y
−
1
/
y
⇒
T
2
=
517.22
k
So actual difference in enthalpy
(
h
2
′
−
h
1
)
=
C
p
(
T
2
−
T
1
)
0.85
=
1.005
(
517.22
−
310
)
0.85
=
245
k
J
/
k
g
1
© examsnet.com
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