Argon gas is compressed steadily from 100 kPa and 25°C to 700 kPa at a rate of 0.15 kg/min by an adiabatic compressor. If the compressor consumes 35 kW of power while operating, the isentropic efficiency of this compressor is
A)6.6%
B)47%
C)65%
D)100%
E)0.78%

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=0.5203 "kJ/kg-K"
Cv=0.3122 "kJ/kg.K"
k=1.667
m=0.15 "kg/s"
T1=25 "C"
P1=100 "kPa"
P2=700 "kPa"
W_comp=35 "kW"
T2s=(T1+273)*(P2/P1)^((k-1)/k)-273
W_s=m*Cp*(T2s-T1)
Eta_comp=W_s/W_comp
"Some Wrong Solutions with Common Mistakes:"
T2sA=T1*(P2/P1)^((k-1)/k) "Using C instead of K"
W1_Eta_comp=m*Cp*(T2sA-T1)/W_comp
W2_Eta_comp=m*Cv*(T2s-T1)/W_comp "Using Cv instead of Cp"

Argon Gas Is Compressed Steadily from 100 KPa and 25°C