Refrigerant-Oil Mixtures and Local Composition Modeling

摘要

The solubility and miscibility refrigerant-oil mixtures are important in understandingthe performance of refrigeration and air-conditioning systems. The objective of this studywas to provide useful information on the thennophysical properties of new refrigerant-oilmixtures and to evaluate candidate mixture models.In this report, the effect of a polyol ester lubricant on equilibrium pressure, liquiddensity, and viscosity is presented for R-22, R-125, R-134a, and AZ20 (50% R-125, 50%R-32) at varying temperatures and concentrations. Deviations from ideal mixture behaviorare interpreted using activity coefficients and may be manifested in three ways: positive,negative, or mixed deviations from Raoult's law. The departure from Raoult's law isrelated to molecular size differences and intennolecular forces in the mixture. Six differentmodels are used to correlate the experimental data: Wilson's relation, the Heil equation, theNon-Random Two Liquid (NRTL) model, the Universal Quasi-Chemical (UNIQUAC)theory, and two different extensions of Wilson's relation. Interaction parameters for all sixmodels are developed from the experimental data (and data from a previous ACRC researchproject). A comparison of the pressure predictions (activity coefficients) for each modelover a wide range of mixture compositions and temperatures shows that the Heil equationhas the best overall penonnance. The Heil equation correlates the saturation behavior ofthese mixtures with an average error less than 6%. The report is organized as follows:Chapters 1 & 2: Background material and research objectives.Chapter 3: A detailed description of the apparatus and test procedure. Acomparison of measurements from this apparatus to ASHRAE data.Chapter 4: Experimental data: mixture pressure as a function of liquid massfraction and temperature; liquid density as a function of liquid massfraction and temperature; viscosity as a function of temperature and liquidmass fraction. Oil density data and limited miscibility results (see alsoAppendix D).Chapter 5: Data analysis background (see also Appendix A).Chapter 6: Mixture modeling background (see also Appendices B, C, &E).Chapter 7: Interaction parameters for all mixtures and models are provided,and a detailed comparison of model performance is given.Chapter 8: A very brief summary of conclusions and recommendations.