Synthetic lubricants have been developed to overcome the problems and shortcomings associated with mineral oils used in refrigeration compressors. Synthetic oils were originally developed to overcome partial compatibility disadvantages of mineral oils used in the R-22 and R-502 systems. With the development of nonchlorinated refrigerants, search for new syndietic oil was enhanced by the fact that these refrigerants have very low characteristics of compatibility with mineral oils. Synthetic oils are produced by combining atoms and molecules of their components in the presence of a catalyst, and dian fractional their distillation of oil.
These oils overcome some die problems associated with mineral oils, including wax precipitation, limited compatibility with some refrigerants, carbonization and degrading elastomers used for o-rings, gaskets and seals. Syndietic lubricants also improved high temperature stability, slipperiness and better viscosity-temperature characteristics, if diey bred for refrigerants. These features reduce power requirements, cold compressors, diey start because the oils have a lower viscosity at low temperatures.
Although they have a lower viscosity at low temperatures, synthetic oils also maintain a high viscosity levels during normal operation of the compressor temperatures, thus providing the best hydrodynamic seal. They also have the best characteristics of seals, improves die volumetric efficiency of the compressor.
Some of the most popular syndietic lubricants selected for cooling duty poly-alpha-olefins, polyglycols, polyol esters and alkylbenzenes.
Polyalphaolefins (PAOs), lubricants choice for use with screw compressors with R-12 and R-114 and heat pumps. They improve mechanical and compression efficiency of these systems, because diey maintain a high viscosity with these mixed refrigerants under diluted conditions. Low temperature fluidity PAOs make these synthetic oils is desirable to use with R-13 and R-503 direct expansion dry-type evaporator systems, which operate at temperatures below 100F (73.3C). They are also used as immiscible oil ammonia in systems where low temperature fluidity and high viscosity index allows evaporator temperature below 50F (45.6C) while retaining sufficient viscosity for a good lubricant to the higher temperatures of the compressor associated with these systems.
Polyalkylene glycols (T), which are normally used in the automotive cooling systems using R-134a. They have higher lubricating properties and low pour point, than mineral oils, which makes them a good option for these applications. Another important characteristic of T that they do not adversely react with elastomeric seals used in these systems. Mineral oils tend to produce a elastomers swell or decompose, leading to leaks in the hermetic system.
Polyol esters are the main lubricants working with emerging HFC refrigerants, in particular R-134a and the blends R-32 and R-507, and R-407c).
Alkylbenzenes are synthesized in a straight or branched chains, such as those in paraffin, mineral oils. They, as a rule, lower than the cost of other synthetic lubricants and work mainly with R-22 and R-502. Alkylbenzene oils have a better solubility, high temperature and chemical stability dian mineral oils which they replace.
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