Consider the following statements in respect of vapor compression refrigeration units: 1. In actual units the refrigerant leaving the evaporator is superheated 2. Superheating of refrigerant at the exit of evaporator increases the refrigerating effect 3. The superheating of refrigerant increases the work of the compressor Which of the above statements are correct?

Option 4 : 1, 2 and 3

In actual refrigeration units the vapour is in superheated state, this superheating is achived using a heat exchanger in which the liquid refrigerant coming out of the condenser which is subcooled and the refrigerant in the evaporator is superheated.

Superheating of the refrigerant in the evaporator will increase the refrigerating effect.

1-2-3-4-1 is the basic cycle where there is no superheat the refrigerating effect achieved here is

h₁ – h₄ and the superheated cycle is given by 1’-2’-3-4-1’ in this cycle the refrigerating effect achieved is given by h_1’ – h_4’ which is clearly greater than the h₁ – h₄.

Now the compressor work will also increase as the work done without superheating is given by h₂ – h₁ and work input when the refrigerant is superheated h_2’ – h_1’ which is greater than h₂ – h­₁

The work input to the compressor is the function of temperature of the refrigerant if the refrigerant is superheated the work of compressor will also increase.