- Freezing point. Must be lower than any temperature existing in the system to avoid freezing in the evaporator.
- Latent heat in evaporation. Must be as high as possible so that a small amount of liquid can absorb a large amount of heat.
- Specific volume. Specific volume must be as low as possible in order to avoid bulky equipment in aspiration and compression lines.
- Density. Must be high in order to use small liquid lines.
- Condensation temperature must be as low as possible at maximum working pressure.
- Boiling temperature, relatively low at close to atmospheric pressure.
- Critical point: as high as possible.
- Liquids must not be flammable, corrosive or toxic.
- Because they must interact with compressor lubricants, must be miscible in the liquid phase and innocuous when combined with oil.
- Refrigerants are used in many systems to cool the compressor motor -normally an electrical engine- so they must be good dielectric substances, meaning with low electricity conducting properties.
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