Refrigerator Or Heat Pump - Practice Questions & MCQ

A refrigerator or heat pump is basically a heat engine run in the reverse direction.

It consists of three parts
1. Source: At higher temperature T₁
2. Working substance: It is called refrigerant. I.e liquid ammonia and freon works as a working substance.
3. Sink: At lower temperature T₂.

• Working of refrigerator

As shown in the above figure, The working substance takes heat Q₂ from a sink (contents of refrigerator) at lower temperature T₂, 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).

• Use of refrigerator-

  The cold body is cooled more and more with the help of a refrigerator. Because the refrigerator transfers heat from a cold to a hot body at the expense of mechanical energy supplied to it by an external agent.

• Coefficient of performance ()-

The coefficient of performance is defined as the ratio of the heat extracted from the cold body to the work needed to transfer it to the hot body.

A perfect refrigerator is one which transfers heat from cold to a hot body without doing work.

• Carnot refrigerator-

So using 

we get 

where T₁ = temperature of surrounding, T₂ = temperature of cold body and  

  when T₂ = 0 then 

I.e  if the cold body is at the temperature equal to absolute zero, then the coefficient of performance will be zero

• The relation between    and  of the refrigerator