Consider a refrigerator that operates on the vapor compression refrigeration cycle with R-134a as the working fluid. The refrigerant enters the compressor as saturated vapor at 140 kPa, and exits at 900 kPa and 70°C, and leaves the condenser as saturated liquid at 900 kPa. The coefficient of performance of this refrigerator is

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Quizplus · Accepted Answer

Solved by EES Software. Solutions can be verified by copying-and-pasting the following lines on a blank EES screen. 
P1=140 "kPa"
P2=900 "kPa"
T2=70 "C"
P3=P2
P4=P1
h1=ENTHALPY(R134a,x=1,P=P1)
s1=ENTROPY(R134a,x=1,P=P1)
h2=ENTHALPY(R134a,T=T2,P=P2)
h3=ENTHALPY(R134a,x=0,P=P3)
h4=h3
COP_R=qL/Win
Win=h2-h1
qL=h1-h4
"Some Wrong Solutions with Common Mistakes:"
W1_COP = (h2-h3)/(h2-h1) "COP of heat pump"
W2_COP = (h1-h4)/(h2-h3) "Using wrong enthalpies, QL/QH"
W3_COP = (h1-h4)/(h2s-h1); h2s=ENTHALPY(R134a,s=s1,P=P2) "Assuming isentropic compression"

Consider a Refrigerator That Operates on the Vapor Compression Refrigeration