A piston-cylinder device contains R-134a. Initially the phase is saturated vapor

Question

A piston-cylinder device contains R-134a. Initially the phase is saturated vapor at 160 kPa. The system then undergoes the following cycle: 1 rightarrow 2 Adiabatic compression to 700 kPa and 35 degree C. 2 rightarrow 3 Isobaric heat rejection to a saturated liquid. 3 rightarrow 4 Isochoric heat rejection. 4 rightarrow 1 Isobaric expansion to the initial state. Diagram this cycle on a P - v diagram. Based on the diagram will the net work be into or out of the system? The diagram is showing a counter clockwise flow so it is not work into the system. Determine the heat and work associated with each process and enter in the table below. When you enter your results please indicate heat/work entering the system as positive and heat/work leaving the system as negative. Please do your work on additional sheets and attach to the end of this document. What is the net work associated with this cycle?

Explanation / Answer

For R134a

T1= -15'c, h1=390,s1=1.736

and now for state 2

saturation temperature for 700kPa =27'c,hg=413, sg=1.713,Cpg=1.04

so, h2=413+(35-27)*1.04=421.32

for state 3

h3=hf=237

for state-4 (-15'c)

since process 3-4 is isenthalpy so

h3=h4=237

(a)1-2

Q=0, W= h2-h1=31.3kJ/kg

(b)2-3

Q=h2-h3=184.3kJ/kg,W=0

(c)3-1

Q=0 , W=0 (since it will be isoenthalpy and adiabatic )

(d)4-1

Q=h1-h4=h1-h3=153kJ/kg,W=0

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