Study Of Thermophysical Properties Of Carbon Dioxide And PAG Lubricant Mixtures

As an environmentally-friendly working fluid, CO₂ has become the spotlight in the field of refrigeration and air conditioning. It is important to choose proper lubricant in the vapor-compression. The contents of lubricants and its influence on heat transfer are introduced in this paper. Although the proportion of the lubricant is low in the system, it constitutes the gas-liquid binary mixtures which adhere to the wall of heat exchanger. The solubility of CO₂ in PAG lubricant varies with the temperature and pressure, which makes the heat transfer mechanism more complex.Because of the exceeding critical temperature of refrigerant (about 31℃) in both gas cooler and compressor, CO₂ becomes a supercritical fluid, which is analyzed in this paper. Thermophysical properties of PAG lubricant are calculated based on existing equations.So far, the research available on thermophysical properties of CO₂ and PAG mixtures based on thermodynamic equations is not much.In this paper the general thermodynamic equations and mixed rules are introduced. The properties of the CO₂ and PAG mixture are analyzed based on the thermodynamic equation model.The solubility of CO₂ in PAG lubricant is obtained. The solubility equations about temperature at constant pressure are fitted. The phase equilibria of binary mixtures is investigated.Thermophysical properties of CO₂ and PAG mixtures are calculated based on existing equations. The results show that solubility of CO₂ in PAG lubricant has an important effect on the properties of PAG. At last, CO₂ and PAG mixtures were observed by means of visualization testing apparatus designed by ourselves. The solubility of CO₂ in PAG lubricant was observed directly.