Refrigeration & Equipment Engineering

 Unit 4 - Refrigerants

4.2.2.Thermodynamic properties
Boiling temperature
The boiling temperature of the refrigerant at atmospheric pressure should be low, if the boiling temperature of the refrigerant is high, the compressor should be operated at high vacuum and the operating cost will be on the higher side.

Freezing temperature
The freezing temperature of a refrigerant should be well below the operating evaporator temperature

Evaporator and condenser pressure
Both evaporator and condenser pressure should be positive (i.e above atmosphere)

Latent heat of vaporization
A refrigerant should have a high latent of evaporation at the evaporator temperature. The high latent heat results in high refrigerating effect per kg of refrigerant circulated which reduces the mass of refrigerant to be circulated per tonne of refrigerant

Critical temperature and pressure
The critical temperature of refrigerant is the highest temperature at which it can be condensed to a liquid, regardless of a higher pressure the critical temperature should be higher than condensing temperature that might be encountered



Coefficient of performance and power requirements
For al ideal refrigerant operating between -15^oC evaporator temperature and 3^oC condenser temperature the theoretical cycle is 5.74,





Specific volume
The specific volume of the refrigerant vapour at evaporator temperature (volume of suction vapour to the compressor) indicates the theoretical displacement of the compressor