7.8 A refrigeration cycle uses refrigerant 134a. The evaporator runs at a temperature of -15°F and the condenser at a te

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7 8 A Refrigeration Cycle Uses Refrigerant 134a The Evaporator Runs At A Temperature Of 15 F And The Condenser At A Te 1 (215.55 KiB) Viewed 14 times

7.8 A refrigeration cycle uses refrigerant 134a. The evaporator runs at a temperature of -15°F and the condenser at a temperature of 80°F. The exit from the condenser is saturated liquid and enters an expansion valve before entering the evaporator. Saturated vapor exits the evaporator. a) For a cooling rate of 5 Btu/s, 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 is modified by the inclusion of a countercurrent heat exchanger between the condenser and the throttle valve in which heat 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 the three cases described above, determine the coefficient of performance for isentropic compression of the vapor.