Classification of Refrigerants:
Refrigerants may be broadly classified depend on the following:
Working Principle
Under this, we have the prime or common refrigerants & the secondary refrigerants.
The prime refrigerants are those which pass by the procedure of compression, cooling or condensation, evaporation and expansion or warming up throughout cyclic processes. R12, R22, carbon dioxide , Ammonia come under this class of refrigerants.
Alternatively the medium that does not go through the cyclic procedure in a refrigeration system and is just utilized like a medium for heat transfer are referred to like secondary refrigerants. Brine solutions, water of sodium chloride & calcium chloride come under this category.
Safety Considerations
Under this, we have the three sub-divisions as follow.
Safe refrigerants
These are the non-toxic, non-flammable refrigerants like R11, R12, R13, R14, R21, R22, R113, R114, carbon dioxide, methyl chloride, water etc.
Toxic and moderately flammable
Dichloroethylene methyl format, sulphur dioxide, ethylchloride, ammonia etc. come under this category.
Highly flammable refrigerants
The refrigerants come under this category are, isobutene, butane, ethane, propane methane, ethylene etc.
Chemical Compositions
They are further sub-divided as following
Halocarbon compounds
These are attained by replacing one or more hydrogen atoms in methane or ethane with halogens.
Azeotropes
These are the mixtures of two or more refrigerants and acts as a compound.
Oxygen and Nitrogen Compounds
Refrigerants with either nitrogen or oxygen molecules in their structure, such like ammonia, are separately grouped and contain a separate nomenclature from the halogenated refrigerants.
Cyclic organic Compounds
The compounds which come under this class are R316, R317 and R318.
Inorganic Compounds
These are further categorized into two categories: Cryogenic & Non- cryogenic.
Cryogenic fluids are those that are applied for attaining temperatures as low as - 160 0C to - 273 0C. Above this temperature range, we may use a multi-stage refrigeration system to realise the wanted temperature. However below - 160 0C, it is not possible as the COP of the cycle becomes very low. To achieve temperatures below - 160 0C, we utilize refrigerants such as, oxygen, nitrogen, hydrogen, helium etc. and for temperatures near to - 273 0C, magnetic cooling is employed.
The inorganic compounds that are employed above the cryogenic temperature ranges come under the remaining sub-division of inorganic refrigerants.
Unsaturated Compounds
Compounds like propylene, ethylene etc. are grouped under this head & grouped under the 1000 series for convenience.
Miscellaneous
This group contains those compounds that cannot be grouped under the other components. They are mentioned by the 700 series along the last numbers being their molecular weight. For example carbon dioxide, air, sulphur dioxide etc.
Since we can see from the above sub-divisions, they are not equally exclusive. A compound can come under more than one sub-division. Therefore, the significance of adopting the several naming conventions to designate the different refrigerants may not be underestimated.