Influence of refrigerant on viscosity and pressure-viscosity coefficient of refrigeration compressor lubricants

摘要

Following the introduction of non-chlorinated HFC (hydrofluorocarbon) refrigerants and polyolester lubricants, designers of refrigeration compressors have had to re-evaluate their knowledge of compressor bearing lubrication. The higher solubility and the lack of anti wear protection in comparison to the traditional refrigerant/lubricant mixes makes the lubrication of bearings using modem Systems a much more difficult task than before. A modem twin screw compressor contains several highly loaded oil lubricated, metal-to-metal including, rolling element bearings, gears and the rotors. These types of contacts are normally referred as EHD or EHL contacts (Elastohydrodynamic-Lubrication), due to elastic deformation of the surfaces. The expected life of these contacts is closely related to the lubricant film thickness. The lubricant properties that determine the film thickness in an EHD-contact include the dynamic viscosity, η, and the pressure-viscosity coefficient. α. In a refrigeration system, both those parameters are affected by the presence of refrigerant, the actual effect depending on the proportions of oil and refrigerant. A falling ball viscometer has been used to measure the viscosity and hence determine the pressure-viscosity coefficient as a function of the amount of dissolved refrigerant. A polyolester oil was tested with refrigerants R-22, R-134a, R-410a and R-32 at 40° and 80°C, at refrigerant concentrations from 0 % to 30 % dilution. It has been shown that the Eyring equation can be used predict the pressure-viscosity coefficient of a mixture based on the molecular weight ratio of the refrigerants.