Explain the working of a refrigerator

A refrigerator is the reverse of a heat engine. Here the working substance extracts heat Q2 from the cold reservoir at temperature T2, some external work W is done on it and heat Q1 is released to the hot reservoir at temperature T1.

In a refrigerator the working substance (usually, in gaseous form) goes by the following steps: 

(a)  Sudden expansion of the gas from high to low pressure which cools it and changes it into a vapour-liquid mixture, 

(b)  Absorption by the cold fluid of heat from the region to be cooled changing it into vapour.

(c)  Heating up of the vapour because of external work done on the system, and  

(d)  Release of heat by the vapour to the surroundings, bringing it to the initial state and completing the cycle.