Lubricants for HFC Refrigerant Compressors

Abstract

To arrest the depletion of ozone layer, CFC-12, which has been widely used in automobile air conditioners or household refrigerators, is being replaced by an alternative refrigerant HFC-134a. At this juncture, it is not possible to maintain the same level of reliability and refrigeration performance when the CFC refrigerant alone is replaced by HFC-134a. A new refrigerant requires a new system and other materials to complement it, and the development of those materials is urgently needed. Among those materials, the development of suitable refrigeration compressor lubricant is of utmost importance in securing good performance, since the lubricant characteristics directly influence the durability of compressors. This paper examines refrigeration lubricants, polyol esters and polyalkylene glycols as to their miscibility with HFC-134a, lubricity and chemical stability, since those properties are indispensable to lubricants used in any kind of refrigerant compressors. Among those, miscibility is determined solely by the molecular structures, while lubricity and chemical stability can be improved mainly by additives. It is possible to give the lubricant well-balanced properties by modifying chemical structures of base oils and by mixing various kinds of additives. There still remain some problems to be solved, however, before the reliability of refrigerating system is enhanced even more, including: (a) finding the rate of additive consumption, (b) examining the interaction among additives, (c) investigating the effects of the interaction among additives on other properties such as chemical stability, lubricity and others. Moreover, it should be taken into account that no matter how excellent the lubricity of the lubricant be, lubricity drops sharply as refrigerant dilution ratio increases.