Question

Superheating in a refrigeration cycle is –
A) increases COP
B) decreases COP
C) no change
D) unpredictable

Answer 1

The solution to this problem can be answered only by studying the principles of working of a refrigerator. The refrigerator acts as a reverse heat engine which lowers the temperature by external work. The amount of work done is dependent on many factors.

Complete step by step answer:
The refrigerators are the heat pumps which are used to lower the temperature of a given volume by doing work on fluid. The refrigerators work on a reverse Carnot cycle. The cool liquid passing through a chamber which is warmer does work on this fluid to convert it into the gaseous form thus lowering the temperature in the chamber. This process continues so as to bring the temperature of the chamber to a required temperature.

The quality or efficiency of performance of a refrigerator is determined by the coefficient of performance (COP) which is the ratio of the heat supplied or the work done by the air in the chamber to the work required by the system.
$COP=\dfrac{Q}{W}$
The work done W is the external work provided to the system for this non-spontaneous process to happen, in our case the electrical energy.
The superheating is the process in which the excess amount of heat is provided to the coolant. This increases the rate of cooling, which is a good indicator for COP.
But also, we should understand that if superheating occurs in a refrigerator, the external energy should be greater to keep the cycle moving.
From the above observations, the coolant evaporates faster adding efficiency of the system, on the other hand, the W required by the system increases, which clearly denotes a decline in the efficiency or the coefficient of performance of the refrigerator.
We get to know that the COP either increases or decreases when superheating takes place in a refrigerator, it is not consistent and therefore unpredictable.

So, the correct answer is “Option D”.

Note: The refrigerator is a reverse heat engine which needs external work like the electrical energy to move the colder air from the chamber to the hotter environment according to the Second law of thermodynamics. The COP of refrigerator is to be maintained at a certain level for the best performance.