Vapor−Liquid Equilibria Predictions for Alternative Working Fluids at Low and Moderate Pressures

Alternative working fluid mixtures containing hydrofluoroethers, hydrofluorocarbons, alkanes, alcohols, ketones, and esters widely used as process fluids generally exhibit azeotropes, high nonideality, and association effects. In this work, the vapor−liquid equilibria for these mixtures are predicted using a combination of the Soave−Redlich−Kwong equation of state, zero reference pressure G E −EoS mixing rules, and the UNIFAC group contribution model. A new functional group assignment strategy was developed, and the model interaction parameters between groups were obtained from selected binary vapor−liquid equilibria data to give fairly good agreement between the calculated results and the experimental data. The method is also extended to ternary systems for VLE representations in a totally predictive manner with only the molecular structures, the critical parameters, and the acentric factors of the pure components needed.