Refrigerants are used in the process of refrigeration, which is a process whereby heat is removed from a substance or a space. A refrigerant is a substance that picks up latent heat when it evaporates from a liquid to a gas.

This is done at a low temperature and pressure. A refrigerant expels latent heat when it condenses from a gas to a liquid at a high pressure and temperature. The refrigerant cools by absorbing heat in one place and discharging it in another area.

The desirable properties of a good refrigerant for commercial use are:
• Low boiling point
• Safe, nontoxic
• Easy to liquefy and moderate pressure and temperature
• High latent heat value
• Operation on a positive pressure
• Not affected by moisture
• Mixes well with oil
• Noncorrosive to metal

There are other qualities that all refrigerants have: molecular weight, density, compression ratio, heat value, and compression temperature. These qualities will vary with the refrigerant used. The compressor displacement and type or design will also influence the choice of refrigerant.

Refrigerants are classified according to their manner of absorption or extraction of heat from substances to be refrigerated:

• Class 1 refrigerants are used in the standard compression type of refrigeration systems
• Class 2 refrigerants are used as immediate cooling agents between Class 1 and Class 3 types and the substance to be refrigerated
• Class 3 refrigerants are used in the standard absorption type of refrigerating systems

Class 1 refrigerants cool by absorption or extraction of latent heat from the substances. Class 2 refrigerants cool substances by absorbing their sensible heats. They include air, calcium-chloride brine, sodium-chloride (salt) brine, alcohol, and similar non-freezing solutions.

Class 3 refrigerants consist of solutions that contain absorbed vapors of liquefiable agents or refrigerating media. These solutions function through their ability to carry the liquefiable vapors. The vapors produce a cooling effect by the absorption of latent heat. An example is aqua ammonia, which is a solution composed of distilled water and pure ammonia.

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