Question

The formation of frost on cooling coils in a refrigerator:
A. Improves the C.O.P of the system
B. Increase the power consumption
C. Reduce the power consumption
D. Increase the heat transfer

Answer 1

A refrigerator is a device which is used to keep things at a temperature lower than that of surroundings. It is based upon the principle that cooling is caused by evaporation. Frost build-up on cooling coils when warm, humid air from surroundings combines with the cold and dry air inside the refrigerator. Frost works as an insulator to heat.

Complete answer:
In a refrigerator, the temperature of cooling coils is typically below the freezing point of water. If the cool air of the compartment meets hot or humid air out of the compartment, the water vapour condenses and settles on the cooling coils. In time, it build-ups a thin layer of frost on the cooling coil.

Since frost is not a good conductor of heat, the fridge goes into reverse i.e., warming the cooling coils. This causes the machinery parts of the fridge to run longer to keep things cool inside it. Therefore, the overall power consumption increases.

Hence, the correct option is B.

Note: A refrigerator can be treated as the reverse of Carnot’s engine. A Carnot engine takes heat from a source at high temperature and rejects a part of it to the sink at a low temperature. The working of a refrigerator is in accordance with the second law of thermodynamics. According to the second law of thermodynamics, heat cannot be transferred from a body at low temperature to a body at high temperature without the application of an external work agency.