3.16 In Example 3.15, it was demonstrated that refrigeration cycles utilizing a heat input to accomplish refrigeration tend to have a low COPC, but a higher exergetic efficiency compared to vapor compression refrigeration cycles using electricity to run a compressor. Consider the combined cycle shown in Figure P3.16 that utilizes a heat input to accomplish refrigeration.

The refrigerant used in the cycle is R-143m (trifluoromethyl methyl ether), an environmentally friendly refrigerant with low ozone depletion potential (ODP)

and low global warming potential (GWP). (R-143m is one of the fluids available in EES.) The R-143m enters the turbine at 1500 kPa, 100°C, and expands to 500 kPa.

The isentropic turbine efficiency is 86%. After expansion, the refrigerant is fully condensed in the condenser. A pump with an isentropic efficiency of 64% is used to raise the R-143m pressure back to the boiler pressure. At the condenser exit, the refrigerant flow splits; some going through the power loop just described, and the rest going through the refrigeration loop, where the SET is −10°C. The R-143m exits the evaporator as a saturated vapor, after which it is compressed to the condensing pressure through a compressor with an isentropic efficiency of 75%. The turbine delivers just enough power to run the compressor; there is no net power delivery from the cycle. The refrigeration capacity of the cycle is 80 tons. Pressure drops through connecting piping can be considered negligible.