Refrigerant R-134aa leaves the evaporator of a refrigeration unit as saturated v

Question

Refrigerant R-134aa leaves the evaporator of a refrigeration unit as saturated vapor at - 10 degree F, and enters the compressor. It leaves the compressor at 140 degree F and 140 psia. Assume adiabatic compression. Estimate the required work of compression in Btu/lb R-134aa compressed. Estimate the entropy change of the R-134a (Btu/lb-degree R) as 1 lb is compressed. Estimate the total entropy generated. Use 1 lb of R-134a compressed as the basis. Estimate the minimum possible work of compression in Btu/lb R-134aa compressed. A reversible cycle operates between a hot thermal reservoir at T_H and a cold thermal reservoir at T_C. It does not transfer heat to any other bodies. Assume T_H = 300 degree C and T_C = 30 degree C Estimate the efficiency (%) of the cycle if it is used as a heat engine.

Explanation / Answer

3) efficiency = 1 - Tc / Th

= 1 - (273 + 30) / (273 + 300)

= 0.4712

so the efficiency is 47.12 %

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