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In refrigeration cycle sub cooling occurs when

In refrigeration cycle sub cooling occurs when Correct Answer Sensible heat from refrigerant is removed

Explanation:

Refrigeration:

The purpose of refrigeration is to cool spaces, objects, or materials and to maintain them at temperatures below the temperature of the surrounding atmosphere.

Refrigeration cycle:

In a refrigeration cycle, the refrigerant must alternate between low temperatures and high temperatures. When the refrigerant is at low-temperature, heat flows from the space or object to be cooled to the refrigerant. When the refrigerant is at a higher temperature, heat flows from the refrigerant to a condenser. The energy supplied as work is used to raise the temperature of the refrigerant to a high enough value so that the refrigerant will be able to reject heat to the condenser.

Vapour compression cycle:

Additional Information 

Superheating:

  • The temperature of heat source will be a few degrees higher than the evaporator temperature, hence the vapour at the exit of the evaporator can be superheated by a few degrees.
  • If the superheating of refrigerant takes place due to heat transfer with the refrigerated space (low-temperature heat source) then it is called as useful superheating as it increases the refrigeration effect. On the other hand, it is possible for the refrigerant vapour to become superheated by exchanging heat with the surroundings as it flows through the connecting pipelines. Such superheating is called as useless superheating as it does not increase refrigeration effect.  

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Useful superheating increases both the refrigeration effect as well as the work of compression.

Hence the COP (ratio of refrigeration effect and work of compression) may or may not increase with superheating, depending mainly upon the nature of the working fluid.

Even though useful superheating may or may not increase the COP of the system, a minimum amount of superheat is desirable as it prevents the entry of liquid droplets into the compressor. The figure shows the VCRS cycle with superheating on P-h and T-s coordinates. As shown in the figure, with useful superheating, the refrigeration effect, specific volume at the inlet to the compressor and work of compression increase. Whether the volumic refrigeration effect (ratio of refrigeration effect by specific volume at compressor inlet) and COP increase or not depends upon the relative increase in refrigeration effect and work of compression, which in turn depends upon the nature of the refrigerant used.

The temperature of the refrigerant at the exit of the compressor increases with superheat as the isentropes in the vapour region gradually diverge.

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