Where the refrigerant is critical to the cooling performance of the refrigeration system, refrigeration oil is essential for the correct operation of the compressor. Lubricants for refrigeration compressors reduce friction, prevent wear and act as a seal between the high and low-pressure sides.

While the primary function of refrigeration oil is still to lubricate, it should also be able to withstand extreme temperature differences and be compatible with refrigerants.

The most common refrigeration cycle is accomplished by circulating, evaporating, and condensing refrigerant in a closed system. Evaporation occurs at low temperature and low pressure, while condensation occurs at high temperature and high pressure. This makes it possible to transfer heat from low-temperature areas to high-temperature areas.

CFCs (Chlorofluorocarbons): These refrigerants are the most harmful to the ozone layer. Examples: R11, R12, R13, R13b1, R14, R113, R114, and R115.

HCFCs (Hydrochlorofluorocarbons): These refrigerants are slightly harmful to the ozone layer. Example: R21, R22, and R123.

HFC (Hydrofluorocarbon): These refrigerants are not harmful to the ozone layer. Mineral oils, PAOs, or alkylbenzenes are not compatible with HFCs. Examples: R134a (for automotive air conditioning systems) and R152a.

Ammonia (R717(NH3)): Although ammonia is environmentally friendly, pure ammonia gas is very toxic to humans. Ammonia is widely used in large industrial refrigeration plants.

There are also mixtures of CFC, HCFC, and HFC refrigerants on the market. Examples of such mixtures are R500 (=R12/R152a), R501 (=R22/R12), and R502 (R22/R115).

Refrigeration oil must function properly over a wide temperature range. Refrigeration compressors have a final compression temperature of up to 180℃. Therefore refrigeration oil must be thermally stable. If the oil contains volatile oil fractions, the lighter fractions enter the compressor system as vapors, where they condense and reduce heat transfer efficiency, but also increase the viscosity of the oil.

Refrigeration oil should be chemically stable to avoid reaction with the refrigerant.

The refrigerant/oil mixture can be (partially) dissolved or not. Complete dissolution is good for lubrication but results in a significant drop in compressor viscosity, which increases friction and wears.

For proper operation, the oil/refrigerant mixture should have a viscosity high enough to provide satisfactory sealing and lubrication in the compressor.

When a liquid boils, the added heat is used to increase the kinetic energy of the molecules until they can no longer remain in the liquid phase and turn into a vapor (or gas). This happens at a certain pressure, but if the pressure increases, so do the boiling temperature.

Alkylbenzenes(AB): These refrigeration oils have good thermal and chemical stability. High miscibility with refrigerants. Alkylbenzenes are completely soluble in mineral oil and PAO, so blends can be produced to improve lubricity.

Polyalphaolefin(PAO): These refrigeration oils have good chemical and thermal stability. PAO also has excellent viscosity-temperature properties. Miscibility with refrigerants is low, which is why the main use of PAO in refrigeration is in applications where miscibility is not a concern. PAO causes seal shrinkage, which can be solved by mixing PAO with AB.

Polyol ester (POE): This refrigeration oil is the most common type of synthetic lubricant used with HFC refrigerants such as R134a.

Polyalkylene glycols (PAGs): These refrigeration oils have a high viscosity index and thermal stability. However, PAG is hygroscopic, which means it can absorb water. PAG is soluble in ammonia.

Mineral oils: naphthenic oils have a low pour point, making them more suitable for use at lower temperatures.

Selecting the correct refrigeration oil depends on the size of the compressor and the refrigerant used.

Refrigeration oil should be chemically and thermally stable and not react with the refrigerant. Also very important is how the refrigeration oil interacts with the refrigerant (e.g. solubility) and how the mixture behaves in the compressor. Lubricant-related problems can occur in refrigeration compressors when the lubricant viscosity becomes too low or oil-free.

The above briefly introduces some basic information about refrigeration compressor oil. If you want to buy air conditioners or refrigeration chemicals, please contact us.

ComforPlanet is a professional custom air conditioning and refrigeration chemicals manufacturer. Our products are suitable for many industries, including HVAC, electrical smart small appliances, etc. ComforPlanet is committed to providing you with safe, high-quality, long-lasting HVAC and cost-effective products that allow everyone around the world to breathe clean, comfortable indoor air.