2. A refrigerator with tetrafluoroethane as refrigerant operates with an evaporation temperature of 15F and a condensation temperature of 80F. Saturated liquid refrigerant from the condenser flows through an expansion valve into the evaporator, from which it emerges as saturated vapor (a) For a cooling rate of 5(Btu)/s, what is the circulation rate of the refrigerant? (b) What is the circulation rate of refrigerant if the throttle valve was 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 heat is transferred to vapor from the evaporator. If liquid from the condenser enters the exchanger at 80F and if vapor from the evaporator enters the exchanger at -15 F leaves at 70F, what is the circulation rate of the refrigerant? (d) For each (a), (b), (c), determine the coefficient of performance for isentropic compression of the vapor