Understanding the effect of super heating and sub-cooling in refrigeration system
The performance of vapour compression refrigeration(VCR) system is depending on following two major important processes:
1) Superheating of vapour refrigerant - superheat ensures the refrigerant vapour is heated beyond its boiling temperature for efficient compression
2) Sub-cooling of liquid refrigerant – sub cooling cools the refrigerant liquid below its condensation temperature to enhance heat exchange efficiency
Superheating and sub cooling process will effect the compressor work and cooling capacity of refrigeration system. Diagram of P-H and T-S diagram shows the effect of super heating and sub cooling in the vapour compression cycle.
the vapour leaving the evaporator is generally at temperature lower than the temperature of the surrounding, hence it is necessary to superheat the vapour before its entry into the compressor. Superheating increases the refrigerating effect and amount of compressor work. As we know that increase in refrigerating effect is less as compared to the increase in work supplied, the net effect of superheating is to reduce Coefficient of Performance(COP). The higher the sub-cooling effect the higher is the efficiency of refrigeration system.
The greatest amount of heat is transferred during the change of state. If the refrigerant gas is cooled below saturation temperature by throttling process before expansion process, then the process is called sub cooling.
As the mass flow rate per ton of refrigerant is less, the power input per ton of refrigeration is less. Sub Cooling is achieved by two methods:
1) By installing a sub cooler in series or parallel with condenser and
2) By using a liquid suction heat exchanger
