الفهرس 
IntroductionOnly 14 pages are availabe for public view
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Abstract
Vapor compression refrigeration systems are commonly used for air¬conditioning and many industrial processes, as they are globally used, the selection of the operating refrigerant is paramount. Regardless of technical specifications, it should be environmentally friendly, as per phase out of CFC, HCFC, and HFC refrigerants, a new generation of green refrigerants has attracted wide attention. Therefore, many researches have been made develop new lubricants compatible with these green refrigerants or to improve current lubricants to work with them. Oil is essential in refrigeration systems for many functions like lubrication, sealing, noise reduction, and compressor cooling. Oil mixes with the refrigerant in compressor crankcase or in the compression chamber and is discharged out through the discharge line to the system. Under specific conditions oil could be trapped or retained in the system and does not return back to the compressor causing catastrophic failures and a degradation of equipment efficiency and reliability. Unfortunately, there is a lack of understanding of how oil leaves the compressor and how it should return to its original place. This work presents a review of oil carryover mechanisms, how could oil retention occurs, explains compressor failure mechanisms, and provide the best practices to avoid oil retention and minimize oil circulation rate.