A refrigeration cycle uses refrigerant 134-a as the working fluid. The refrigera

Question

A refrigeration cycle uses refrigerant 134-a as the working fluid. The refrigerant leaves the evaporator as a saturated vapor at 400 kPa. However, the refrigerant enters the compressor at 320 kPa, 10 C. The condenser pressure is 1400 kPa, and the refrigerant leaves the condenser at 4.4 C subcooled. The compressor adiabatic efficiency is 80%. A. Determine the COP for this refrigeration cycle. B. Compare the COP for this refrigeration cycle with the coP of an ideal refrigeration cycle operating between an evaporator pressure of 400 kPa and a condenser pressure of 1400 kPa.

Explanation / Answer

I had shown that for the actual refrigeraton cycle COP = 3.4
now for the ideal case :
saturation temp. corresponding to 400 KPa = 8.9C = 281.9 K = T2

also saturation temp. corresponding to 1400 KPa = 52.4C =325.4K = T1

COPideal = T2 / (T1 - T2) = 281.9 / (325.4 - 281.9) = 6.48

COPactual = 3.4

decrease in entropy = (COPideal - COPactual) / COPideal

   (6.48 - 3.4)/6.48 = 47.5%

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