Refrigerants:
The thermodynamic efficiency of a refrigeration system depends mainly on its operating temperatures. However, important practical issues such as the system design, size, initial and operating costs, safety, reliability, and serviceability etc. depend very much on the type of refrigerant selected for a given application. Due to several environmental issues such as ozone layer depletion and global warming and their relation to the various refrigerants used, the selection of suitable refrigerant has become one of the most important issues in recent times. Replacement of an existing refrigerant by a completely new refrigerant, for whatever reason, is an expensive proposition as it may call for several changes in the design and manufacturing of refrigeration systems. Hence it is very important to understand the issues related to the selection and use of refrigerants. In principle, any fluid can be used as a refrigerant. Air used in an air cycle refrigeration system can also be considered as a refrigerant. However, in this lecture the attention is mainly focused on those fluids that can be used as refrigerants in vapour compression refrigeration systems only.
The refrigerant is a heat carrying medium which during their cycles (i.e. compression, condensation, expansion, evaporation) in the refrigeration system absorb heat from a low temperature system and discard the heat so absorbed to a higher temperature system.
Properties of a good refrigerants:
- Low boiling Point
- High Critical Temperature
- High latent heat of vaporisation
- Low specific heat of liquid
- Low specific volume of vapour
- Non-corrosive to metal
- Non-flammable
- Non-explosive
- Non-toxic
- Low cost
- Easy to liquify at moderate pressure and temperature
- Easy to locating leaks by odour or suitable indicator
- Mixes well with oil.
Mechanical Engineering 