Refrigerant 134a is compressed with no heat transfer in a pi

Refrigerant 134a is compressed with no heat transfer in a piston–cylinder assembly from 30 lbf/in.², 20°F to 120 lbf/in.² The mass of refrigerant is 0.04 lb. For the refrigerant as the system, W = –0.56 Btu. Kinetic and potential energy effects are negligible. Determine the final temperature, in °F.

Solution

From !st law of thermodynamics

dQ=dU+dW

dQ=0 no heat transfer

therfore dU= -dW

U2-U1= 0.56\\0.04 Btu/lb

U2= 14+U1

now at 30psi,20F U1=97.6 btu/lb

U2=97.6+14=111.6 btu/lb

therefore at U2, 120psi

Temperature = 114 F