A piston-cylinder device contains 3.2 kg of R-134a at 400 kPa and 50°C. Now R-134a is allowed to expand at constant pressure until its temperature drops to 10°C. The work done during this expansion process is
A)13 kJ
B)0 kJ
C)4.2 kJ
D)33 kJ
E)58 kJ

Question

Quizplus · Accepted Answer

Solved by EES Software. Solutions can be verified by copying-and-pasting the following lines on a blank EES screen. 
m=3.2 "kg"
P1=400 "kPa"
P2=P1
T1=50 "C"
T2=10 "C"
v1=VOLUME(R134a,T=T1,P=P1)
v2=VOLUME(R134a,T=T2,P=P2)
W=m*P1*(v2-v1) "kJ, constant pressure"
"Some Wrong Solutions with Common Mistakes:"
W1_W=P1*(v2-v1) "Forgetting m"
R=0.08149 "kJ/kg.K"
P1*Vol1=m*R*(T1+273)
P2*Vol2=m*R*(T2+273)
W2_W=m*P1*(Vol2-Vol1) "Assuming ideal gas"
P1*Vol11=m*R*T1
P2*Vol22=m*R*T2
W3_W=m*P1*(Vol22-Vol11) "Assuming ideal gas with deg. C"
W4_W=0 "Assuming work to be zero"

A Piston-Cylinder Device Contains 3