EQUATION OF STATE MODELING OF REFRIGERANT MIXTURES

The vapor-liquid equilibrium behavior of several conventional (hydrofluorocarbon (HFC) and hydrochlorofluorocarbon CHFC)) and proposed (HCFC + alcohol or fluorinated alcohol) binary refrigerant mixtures are studied using a cubic equation of state, three recently developed multiparameter mixing and combining rules, and the conventional one-parameter van der Waals mixing rule. Of particular interest was determining how well these mixing models could correlate experimental data at a single temperature, and then how accurately each could predict phase behavior at other temperatures with temperature-independent parameters. The results indicate that for some of the new refrigerant mixtures only the excess free energy-based equation of state mixing rules can provide acceptable correlations, and also reasonable predictions over a range of temperatures. While all the models considered performed well for conventional refrigerant mixtures, only the excess free energy based-models consistently led to accurate predictions over wide ranges of temperature; the other models result in less accurate predictions and, in same cases, false liquid-liquid phase splitting.