A refrigerator with tetrafluoroethane (Table 9.1. Fig. G.2) as refrigerant operates with an evaporation temperature of - 15(°F) and a condensation temperature of 80(°F).
Saturated liquid refrigerant from the condenser flow s through an expansion valve into the evaporator, from which it emerges as saturated vapor
(a) For a cooling rate of 5(Btu) (s)-1, what is the circulation rate of the refrigerant?
(b) By how much would the circulation rate be reduced if the throttle valve were replaced by a turbine in which the refrigerant expands isentropically?
(c) Suppose the cycle of (a) is modified by the inclusion of a countercurrent heat exchanger between the condenser and the throttle valve in which heal is transferred to vapor returning from the evaporator If liquid from the condenser enters the exchanger at 80(°F) and if vapor from the evaporator enters the exchanger at -15 (°F) and leaves at 70(°F). what is the circulation rate of the refrigerant?
(d) For each of (a), (b), and (c), determine the coefficient of performance for isentropic compression of the vapor.