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31 May 2012

What is special about refrigeration oil?

I was once told by the CEO of an oil company that refrigeration oil represents only about 3 to 4 percent of total business. The market for refrigeration oil is indeed small, but very demanding in terms of technology and procedures. Users who overlook important oil-related issues often later face technical problems with their machines and possible production disruptions. Thus, oil manufacturers and sellers need to be aware of the refrigeration industry’s needs, and at the same time users need to know what to look for on the refrigeration oil market.

When we talk about refrigeration oil, two basic principles play a central role:

  1. The main duty of lubrication oil is to lubricate the contact points in mechanical equipment.
  2. The lubrication oil’s secondary duty is to cool down the generated heat to acceptable levels.

The design of the refrigeration equipment is based on a concept of an interaction between three main systems: the compressor, the oil separator system and the oil supply system.

The oil flows through an oil filter, and then it is cooled by the oil cooler to a temperature range of 45 - 60°C. Next, it is injected in directly into the compressor.

The injected oil must have a lower temperature than the compressed refrigerant, because the colder oil controls the compression temperature. This protects the compressor against overheating during the compression.

After compression, the oil and refrigerant need to be separated again in order for the oil to return to the compressor. This oil should be as clean as possible. Nevertheless, it is estimated that after the separation, approximately 4 percent of the refrigerant remains in the oil. This 4 percent is considered an acceptable amount by most OEMs.

The separation process is influenced by the following factors:

  1. The refrigerant and oil type
  2. The temperature of the oil at the separator entry point

The ideal temperature for separation of the oil and the refrigerant gas is when the adhesion between the oil and the refrigerant gas is at its lowest.

There is always an interaction between the oil and refrigerant, either in the oil separator or in piston compressors when refrigerant is placed on top of the oil. The oil-laden gases enter the separator at a very high speed. Sudden exposure to a large area reduces the velocity of the gases. However, the velocity of the oil particles remains the same. The oil moves down due to gravity, collecting at the bottom of the vessel. The refrigerant will always be forced to the top. In between the oil and refrigerant, a layer of oil-and-gas mixture forms. The higher the pressure of the refrigerant, the stronger this mixture becomes.

In today’s refrigeration industry, oil manufactures need to deal with the following factors:

  • Interaction between oil and refrigerant
  • Lubrication demands and factors that affect them, such as changes in viscosity and chemical changes
  • Oil separation by an unknown system ( the separation process works similar to the oil-production process, and the oil gets transformed after an operational period)
  • Fluctuating working conditions of equipment in the refrigeration system, such as changes in pressure and temperature
  • Partial, limited, incomplete information provided by compressor-block manufacturers to oil manufacturers, typically only covering the lubrication point
  • Actual interactions between refrigerants and oils not always matching predictions due to compressor-unit builders not working with standardized data

Given all above stated points, there is high pressure on oil manufacturers to provide a products that is stable, clear, pure and has a long lifespan. The demand for high-quality engineering and specialized products is huge.

Don’t risk your system on a guess

Don’t guess, or even approximate, which lubricant might be right for your specific refrigeration system. An incorrect choice could result in costly equipment repairs and the headaches of downtime. To make the right lubricant selection, it is recommended that you seek expert assistance from knowledgeable experts who understand how the various lubricant options interact with different refrigerants and refrigeration compressor systems.

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