A positive-displacement oil pump for a refrigerant compressor with a low-pressure chamber has properties that lower performance of oil supply under three conditions: first, when suction pressure becomes lower; second, when oil temperature becomes lower; and third, when oil is mixed with greater amounts of liquid refrigerant. The effects on performance are cumulative. In this paper, we show that the characteristics of oil pumps can be understood by considering foaming gas from oil (= cavitation, which is caused by pressure drops in the oil paths and suction port in the cylinder), because oil pumps for refrigerant compressors circulate oil with dissolved refrigerant. The result of a numerical simulation developed with the assumption that oil is dissolved with saturated refrigerant shows good correlation with the testing of actual compressors.
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