Air is compressed steadily and adiabatically from 15°C and 90 kPa to 310°C and 600 kPa. Assuming constant specific heats for air at room temperature, the isentropic efficiency of the compressor is
A)0.038
B)0.64
C)0.86
D)0.92
E)0.73

Question

Quizplus · Accepted Answer

Solved by EES Software. Solutions can be verified by copying-and-pasting the following lines on a blank EES screen. 
Cp=1.005 "kJ/kg.K"
k=1.4
P1=90 "kPa"
T1=15 "C"
P2=600 "kPa"
T2=300 "C"
T2s=(T1+273)*(P2/P1)^((k-1)/k)-273
Eta_comp=(Cp*(T2s-T1))/(Cp*(T2-T1))
"Some Wrong Solutions with Common Mistakes:"
T2sW1=T1*(P2/P1)^((k-1)/k) "Using C instead of K in finding T2s"
W1_Eta_comp=(Cp*(T2sW1-T1))/(Cp*(T2-T1)) 
W2_Eta_comp=T2s/T2 "Using wrong definition for isentropic efficiency, and using C"
W3_Eta_comp=(T2s+273)/(T2+273) "Using wrong definition for isentropic efficiency, with K"

Air Is Compressed Steadily and Adiabatically from 15°C and 90