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Refrigerator or Heat Pump

A refrigerator or heat pump is basically a heat engine run in reverse direction. It essentially consists of three parts:
Source: At higher temperature, T1.
Working substance: It is called refrigerant liquid ammonia and freon works as a working substance.
Sink: At lower temperature, T2.
The working substance takes heat Q2 from a sink (contents of refrigerator) at lower temperature, has a net amount of work done W on it by an external agent (usually compressor of refrigerator), and gives out a larger amount of heat Q1 to a hot body at temperature T1(usually atmosphere) (Fig. 17). Thus, it transfers heat from a cold to a hot body at the expense of mechanical energy supplied to it by an external agent. The cold body is thus cooled more and more.
Fig. 17
The performance of a refrigerator is expressed by means of “coefficient of performance” β which is defined as the ratio of the heat extracted from the cold body to the work needed to transfer it to the hot body.
i.e., 55538.png
A perfect refrigerator is one which transfers heat from cold to hot body without doing work, i.e., W = 0, so that Q1 = Q2 and hence β = ∞

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