R290, Minimum Viscosity, Lubricant Film Thickness, Bearing, Rotary Compressor
R290 which has been considered for use in room air conditioning systems as low global warming potential (GWP) refrigerant has attracted great attention. This refrigerant is determined the lubrication performance of the sliding parts (especially the bearings) in rotary compressor. It is important to prevent the sliding parts from seizure and wear. To ensure the bearing reliability, it is traditional for R290 compressor manufacturer to specify a minimum oil sump temperature difference above the saturated discharge temperature. It is a surrogate measure of minimum viscosity required to ensure adequate lubricant film thickness in bearings under the system flooding conditions. The minimum viscosity depends on the bearing geometry, the load and the speed. This paper describes a method for specifying the minimum safe viscosity of the high-side R290 rotary compressors based on lubricant film thickness calculations.