The refrigerant retains heat from the low-temperature framework and discards the heat so devoured to a higher temperature system. It is a heat-carrying medium in the refrigeration system. Earlier natural ice and water and salt mixture were the primary refrigerant. In most cycles, it undergoes phase transitions from a liquid to a gas and back to its original state. Halo-carbon component hydrocarbon compounds are used for refrigeration applications. The refrigerant for a specific application is dictated by its physical, thermodynamic and various properties. There is no one refrigerant which can be used for all types of application i.e. there is no ideal refrigerant. On the off chance that one has certain great favorable circumstances which will have a few disservices too.
Classification of Refrigerants
- Primary Refrigerants – are directly used in the system to absorb heat and provide refrigeration.
- Secondary Refrigerant – which is first cooled by the primary refrigerants and then they are used for refrigeration.
Primary Refrigerants are further categorized into four groups
- Halo-Carbons:- R-11, R-12, R-14, R-22, R-134a, etc.
- Azeotrope refrigerants:- R-500, R-502, R-503, R-504, etc
- Inorganic Refrigerants:- R-717 (Ammonia), R-729 (Air), R-744 (Carbon Dioxide), R-118 (Water), etc
- Hydrocarbon Refrigerants:- R-170 (Ethane), R-290 (Propane), R-600 (Butane), R-600a (Isobutane)
Secondary Refrigerants – Brines are generally an example of this type of refrigerants. It is used where the temperature has to be maintained below the freezing point of water.
Properties of a Perfect Refrigerant
An ideal refrigerant should have the following properties as
- Low Boiling and Freezing point
- High critical pressure and temperature.
- High Latent heat of vaporization.
- Thermal conductivity should be high.
- Non-Corrosive to metal
- Non-flammable and non-explosive
- Low cost
- Easily and regularly available
- Easy to liquefy at moderate pressure and temperature
- Easy of finding spills by smell or appropriate pointer
- Mixes well with oil
- High coefficient of performance
- Ozone friendly
Hence, medium is chosen which has greater advantages and less disadvantages.