Outgassing and Absorption Rates of Oil/Refrigerant Mixtures

Knowledge of the solubility characteristics of an oiVrefrigerant mixture is important when analyzing the lubrication system behavior in refrigerant compressors since the solubility significantly affects the viscosity of the mixture. For an operating compressor, the lubricant is a mixture of oil and refrigerant and the viscosity of the mixture is a strong function of the refrigerant concentration and of the mixture temperature. Solubility information is available for various oiVrefrigerant mixtures that gives mixture viscosity as a function of temperature and pressure and can be used adequately under steady-state operating conditions. Accuracy is compromised if this information is used to analyze transient events associated with sudden changes in temperature or pressure such as may occur throughout the lubrication system. For this reason, an analytical model was developed to predict the transient outgassing/absorption rates of an oil/refrigerant mixture experiencing a sudden change in temperature or pressure. The solution method was to develop an oil/refrigerant mixture correlation by employing the conservation laws of mass and energy in a transient system. A test rig was built to accurately measure the characteristics of an oiVrefrigerant mixture experiencing a change in system temperature or pressure so that a comparison could be made between predicted and experimental results. Fast response thermocouples and pressure transducers were used to capture the system behavior during ooth outgassing and absorption events. A summary of the analytical model and experimental verification activities is presented.