Support
Lubricating oils for refrigeration compressors are specifically designed for that application and selection of these lubricants requires special attention and knowledge . Do not mix minerals and polyester oils , as they are not compatible .
The phase-out of CFCs , HCFCs and the latest phase-down of HFCs along with a reduction in global warming gas emission has led to numerous refrigerant / lubricant combinations . Many of these new refrigerants are requiring new lubricants in order for the plant to function correctly .
The essential properties of refrigeration oil are as follows :
• It must be specially made for refrigeration applications
• It must have the right viscosity
• It must have good wear characteristics
• It must be very dry and not contain wax
• It must be miscible with the refrigerant
• It must have chemical , thermal , and hydrolytic stability at both low and high temperatures
Traditionally the lubricant for refrigeration systems has been mineral oil . Mineral oil is relatively inexpensive , has desirable solution characteristics with the traditional refrigerants , is reasonably stable and has been widely available .
Consequences of using the wrong oil :
• Due to bad mixing properties oil return to the compressor is reduced resulting in insufficient lubrication of the compressor .
• Reduced heat transfer in the evaporator and the condenser resulting in reduced system efficiency .
• Excessive foaming of the oil , which can result in liquid slugging .
• Formation of sludge and coke , causing blockages and corrosion .
Until the phase-out of CFC refrigerants , mineral oils were the primary oils used in refrigeration systems . However , mineral oils are not suitable for use with the HFC / HFO refrigerants . The main reason for this incompatibility is the insufficient lubricity ( lubricating ability ) and miscibility ( mixing ability ) of mineral oils . Mineral oils could remain in use with some of the Hydrocarbon refrigerants .
Much work has been done to find acceptable lubricants to use with
HFC / HFO refrigerants . Which oil types are used for refrigeration systems ? Gean , thank you for the question , I will continue on the topic of types of oils in the next issue of the RACA Journal .
REFERENCES : |
1 . |
SARACCA |
2 . |
ACRA |
3 . |
SANS 10147 |
Thank you for all your questions . Send your problems ( and sometimes your creative solutions ) to acra @ netactive . co . za with ‘ Solutions Page ’ in the subject line . You may include pictures . RACA
54
RACA Journal I February 2022 www . hvacronline . co . za