Arefrigerator maintain the cooled space at 2 degree c when the ambient air aroun

Question

Arefrigerator maintain the cooled space at 2 degree c when the ambient air around the refrigerator is 25degree c. The refrigerator has a coefficient of performance of 2.5. The rate of cooling in the refrigerated space is 8000 kj/h. Determine the power consumption of the refrigerator and the heat-transfer rate to the surrounding air. Suppose the refrigerator in problem s-13 is replaced by an energy-conserving unit that has a COP of 4.0. Calculate the power consumption of this unit and the rate of heat transfer to the surrounding air. An automobile engine has a thermal efficiency of 18 percent. The termperature of the fuel is 950 degree c, and the surrounding air is at 25 degree c. Does the operation of this engine violate the second law of thermodynamics Show that beta _H,rev = 1 + beta_R, rev calculate the maximum coefficient of performance for the heat pump specified in problem 5-12. Does the heat pump described in problem 5-12 violate the second law of thermodynamics

Explanation / Answer

COP of a heat pump can be expressed

COP = Qc/ P

P = Qc/ COP = 8000 kJ/h/2.5 = 3200 kJ/h

(b)

The Heat transfer rate to the surrounding air is equal to the rate of cooling in the refrigerated space plus the power consumption rate

H = Qc+ P = 8000 kJ/h + 3200 kj/h = 11200 kj/h

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