Using solubility data for HFC-134a and ester lubricant mixtures to model an in-tube evaporator or condenser
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Refrigeration systems typically have small amounts of lubricant circulating through the evaporator and condenser. However, in the high-quality region of a heat exchanger, the amount of lubricant present in the liquid phase can be significant, thus changing the saturation temperature of the refrigerant/lubricant mixture. In this study, solubility data are used to explain temperature measurements obtained for a refrigerant/lubricant mixture at the inlet and exit of an evaporator and condenser. The significance of these solubility effects on determining two-phase heat transfer coefficients for refrigerant/lubricant mixtures is also discussed. As part of this study, solubility data are presented for HFC-134a and a 169 SUS and 369 SUS penta erythritol ester mixed acid over a temperature range of -10 C (14 F) to 50 C (122.0 F) for lubricant concentrations from 0% to 45%. The data were statistically correlated and solubility equations are presented. The range of temperatures and concentrations evaluated reflects conditions typically found in a refrigeration-type evaporator or condenser.