Heat Rejection by a Refrigerator The food compartment of a refrigerator, shown in Fig. 6–24, is maintained at 4°C by removing heat from it at a rate of 360 kJ/min. If the required power input to the refrigerator is 2 kW, determine (a) the coefficient of performance of the refrigerator and (b) the

Question

Heat Rejection by a Refrigerator The food compartment of a refrigerator, shown in Fig. 6–24, is maintained at 4°C by removing heat from it at a rate of 360 kJ/min. If the required power input to the refrigerator is 2 kW, determine (a) the coefficient of performance of the refrigerator and (b) the rate of heat rejection to the room that houses the refrigerator.

Accepted Answer

The power consumption of a refrigerator is given. The COP and the rate of heat rejection are to be determined.
Assumptions Steady operating conditions exist.
Analysis (a) The coefficient of performance of the refrigerator is

[latex] COP _{ R }=\frac{\dot{Q}_{L}}{\dot{W}_{ ext {net }, ext { in }}}=\frac{360 kJ / min }{2 kW }\left(\frac{1 kW }{60 kJ / min } ight)=3 [/latex]

That is, 3 kJ of heat is removed from the refrigerated space for each kJ of work supplied.
(b) The rate at which heat is rejected to the room that houses the refrigerator is determined from the conservation of energy relation for cyclic devices,

[latex] \dot{Q}_{H}=\dot{Q}_{L}+\dot{W}_{ ext {net,in }}=360 kJ / min +(2 kW )\left(\frac{60 kJ / min }{1 kW } ight)=480 kJ / min [/latex]

Discussion Notice that both the energy removed from the refrigerated space as heat and the energy supplied to the refrigerator as electrical work eventually show up in the room air and become part of the internal energy of the air. This demonstrates that energy can change from one form to another, can move from one place to another, but is never destroyed during a process.

Question 6.3: Heat Rejection by a Refrigerator The food compartment of a r...

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