An agile solution, refrigeration compressor oil performs many roles. It serves as a functional fluid, hydraulic control and dedicated lubricating oil in refrigeration compressors which are operating under the influence of refrigerants.
The lubrication process for refrigeration compressors holds a specific position in terms of lubrication technology. The expected active service life of refrigeration compressors is directly connected to the superior quality which is a requirement of refrigeration compressor oils. The interactions with other substances that the refrigeration compressor oil makes direct contact with, along with the extremely low and high temperatures involved, makes highly specific demands on these carefully formulated lubricants.
The core function of a refrigeration compressor oil is always to lubricate the rotors or pistons of the compressor rotors and to effectively seal the valves or slip ring seals. Additionally, the refrigeration compressor oil must also work to dissipate heat, taking it away from hot components in the compressor and help the sealing process of both valves and compression chambers.
In situations where a dedicated refrigerant is considered critical to deliver the cooling properties of a system, compressor oil is a vital element for the effective operation of compressors. Oils engineered for refrigeration compressors have several jobs to perform. They are required to efficiently cut down friction and stop wearing on the compressor’s components. Oils are also counted on to create a strong seal between the lower and higher pressure sides of the compressor system while always being compatible with the various materials employed to construct components, for example, rubber seals.
What are refrigeration compressors?
To understand refrigeration compressor oils, it is essential to understand the equipment which they are designed to serve. A refrigeration compressor is a product that is designed specifically to raise the temperature, energy level and pressure of a refrigerant vapour via mechanical means as part of one of three refrigeration cycles, economised vapour compression, vapour-compression or transcritical CO2.
How do refrigeration systems work?
The most typical refrigeration cycle works by circulating and evaporating before condensing a selected refrigerant within a closed system. The process of evaporation takes place at low temperature and low pressure, while condensation happens at high temperature and high pressure. As a result, it is possible for heat to be transferred from a low temperature area to a high temperature area.
Refrigerants used include Chloro-Fluoro-Carbon (CFC), Hydro-Chloro-Fluoro-Carbon (HCFC), (Hydro-Fluoro-Carbon, (HFC) and Ammonia (R717 (NH3). However, mixtures of refrigerants also exist which combine CFC, HFC and HCFC refrigerants. Refrigerants are selected based on three important properties, the heat required to vaporise the liquid, boiling point and their densities in vapour and liquid phase.
Refrigeration compressor oil attributes
As mentioned earlier, the primary function of every refrigeration compressor oil is lubrication. However, oils must have many other properties to carry out the variety of tasks they are designed to fulfil. They must have the capability to remain effective under most extreme differences in temperature (both high and low). They must also be fully compatible with specific types of refrigerants that are being used within a system. The following are some of the vital attributes that that refrigeration compressor oils must have.
Solubility
Mixtures containing refrigerant and refrigeration compressor oil can be partly soluble, insoluble, or completely soluble. Full solubility can benefit the lubrication process but can also cause a significant fall in viscosity inside the refrigeration compressor. Unfortunately, this can lead to unwanted wear and friction on the compressor’s components.
As a result, to remain effective, in terms of solubility the refrigerant/compressor oil mixture must have a sufficiently high viscosity to deliver effective sealing as well as lubrication inside the refrigeration compressor.
Chemical stability
Oils designed for refrigeration compressors are required to be chemically stable. This attribute is critical to avoid the possibility of a chemical reaction occurring between the oil and the compressor refrigerant.
Thermal stability
It is crucial that refrigeration compressor oils can function properly across a broad range of temperatures. The reason for this is that the high end of compression temperatures with compressors built for refrigeration can often hit top temperatures that reach up to 180ºC. As a result, these highly specialised oils must have impressive levels of thermal stability. If the compressor oil used includes volatile oil fractions, the light ends can enter the refrigeration compressor system as vapour. This means they can condense resulting in a reduction of heat transfer efficiency and an increase in lubricant viscosity.
It is vital that the correct refrigeration oil is deployed that is designed for both the type of equipment involved and the refrigerant in use. Employing the wrong type of oil can lead to damage and wear to components and expensive downtime for repairs and in some cases, equipment replacement. Always check your OEM specifications before ordering a suitable solution for your compressor.
