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Refrigerant 134a leaves the evaporator as saturated vapor at

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Refrigerant 134a leaves the evaporator as saturated vapor at 1.4bar and is heated at constant pressure to 20 degrees C before entering the compressor. After isentropic compression to 12bar, the refrigerant passes through the condensor exiting at at 44 degrees C, 12 bar. The liquid then passes through the heat exchanger, entering the expansion valve at 12bar. The mass flow rate of refrigerant is 6 kg/min, determine:

a. coefficient of performance
b. compressor power input

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Solution Preview

Please see the attached file.

It's easier to find b first:
b. Compressor power input

Note that the compression stage is isentropic. From the saturation table of R134a:
At 1.4 bar (0.14 MPa) saturated vapor: h1 = 236.04 (kJ/kg), s1 = 0.9322 (kJ/kg.K)
Outlet of compressor: P2 = 12 ...

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