Refrigerant migration and oil sump viscosity change of R290 high-pressure rotary compressor during shutdown process

Propane (R290) has excellent thermophysical properties and development potential. The dynamic characteristics of R290 rotary compressors and room air conditioners have been studied mainly on the start-up and defrost processes. There is little research on the shutdown process. Unlike hydrofluorocarbons (HFCs), the density of liquid propane is lower than that of lubricant. It is difficult for propane to dissolve into the oil sump and downward after the refrigerant separation after shutdown. The shutdown state affects the distribution of refrigerant in the oil sump and the mixture viscosity of the restart-up, which is related to the compressor reliability. In this paper, an R290 room air conditioner system was built and the variations of system pressures, temperatures, and oil sump parameters of an R290 high-pressure rotary compressor with three different lubricants were measured after shutdown in two conditions. As the experiments indicated, driven by the refrigerant supersaturation (the difference between the actual refrigerant solubility and saturation solubility) resulting from the rapid pressure drop after shutdown, a large amount of refrigerant separated from the oil sump, and the refrigerant solubility dropped fast. As the compressor temperature decreased, the bottom viscosity reached a peak. For the low-temperature heating condition, the peak was about 120.4∼160.1mPa•s. However, when the degree of supersaturation decreased to a certain value, the refrigerant no longer separated out. There is always a solubility gradient of refrigerant in the oil sump of R290 high-pressure compressor after shutdown. Its size was related to the pressure drop and the miscibility of lubricants and refrigerants.