Lubrication of R290 Rotary Compressor Used in Low-Temperature Air-Water Heat Pumps

Abstract

Owing to the environmental friendly and low discharge temperature of propane (R290), R290 rotary compressor was proposed to use in low-temperature heat pump (ambient temperature of 7 ∼ -30°C). At present, research on lubricants of R290 rotary compressors used in low-temperature heat pumps is still lacking. Therefore, in this study, the oil sump thermophysical properties (temperature, solubility, and viscosity) of R290 rotary compressors used in low-temperature air-water heat pumps (LT-AWHP) and their influence on the oil film thickness of the bearings were studied experimentally and numerically. The study was conducted under different ambient temperatures (7, -12, -20, and -30°C) with different lubricants (PAG40 and POE68). The results show that under any condition, the oil sump solubility is uniform, and is close to the oil sump inlet saturation solubility (Soup-sat), while the viscosity in the oil sump outlet is higher than that in the oil sump inlet. Additionally, the oil film thickness and performance comparison show that POE68 is more suitable for low-temperature heat pumps than PAG40. We suggest that measures should be taken to decrease the oil sump viscosity under lower ambient temperatures and increase it under higher outlet water temperatures when using POE68. These results would provide guidelines for the choice of oil in the R290 rotary compressor for low-temperature heat pump and thus improving its performance and reliability.