The thermal characteristics of a small dormitory refriderator are determined by

Question

The thermal characteristics of a small dormitory refriderator are determined by performing two separate experemints, each with the door closed and the                     refridgerator placed in ambient air at T (inf)=25 deg C. In one case an electric heater is suspended in the fridge cavity, while the fridge is is unplugged.                     With the heater dissipating 20 W a steady state temperature of 90 deg C is recorded within the cavity. With the heater removed and now in operation the second                     experiment involves maintaining a steady state cavity temperature of 5 deg C for a fixed time interval and recording the electrical energy required to operate                     the fridge. In such an experiment for which steady state operation is maintaned over a 12 hour period, the input electrical energy is 125,000 J. Determine the                     fridges coefficient of performance COP.

Explanation / Answer

cop=desired output/required input,

cop of an fridge is =Ql/Wi

=Ql/Qh-Ql,

=1/(Qh/Ql)-1.

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