A predictive extended corresponding states model for pure and mixed refrigerants including an equation of state for R134a

Abstract

We have developed a predictive corresponding states model for the thermophysical properties of pure refrigerants and refrigerant mixtures. The bulk phase properties such as the density, enthalpy and entropy are predicted using the principle of extended corresponding states, incorporating a recent 32-term modified Benedict-Webb-Rubin correlation for the R134a (1,1,1,2-tetrafluoroethane) reference fluid. This theoretically based model uses shape factors to ensure conformality among the various components. A correlation for the shape factors was found by mapping saturation boundaries of the fluids of interest onto the reference fluid and then fitting the results to an empirical correlation. In this work we present the coefficients for density-independent shape-factor correlations for 21 refrigerants, and a set of universal coefficients that can be used with any refrigerant given only the critical parameters and the acentric factor. We show comparisons with experimental density data for each of the 21 refrigerants. We also demonstrate the use of generalized coefficients for shape factors where only the critical parameters and acentric factors are known. In addition, we present comparisons of the volume prediction for two binary refrigerant mixtures and one ternary refrigerant mixture.