Vapor-liquid equilibrium measurements and correlations for the binary mixture of difluoromethane + isobutane and the ternary mixture of propane + isobutane + difluoromethane

Hydrocarbons such as propane (R-290), n-butane (R-600), and isobutane (R-600a) are expected candidates for CFC, HCFC, and HFC alternative working fluids for refrigerators and heat pump systems. Hydrocarbons (HCs) are environmentally acceptable refrigerants; however, most HCs have the problem of flammability. In order to maintain the safety of home refrigerators and air-conditioners, mixing a small amount of HFCs with HCs may be effective. In our previous study, the vapor-liquid equilibrium (VLE) measurements for the binary mixtures of R-290 + R-600a and the difluoromethane (R-32) + R-290 have already been performed. This study measured the VLEs of the binary mixture of R-32 + R-600a and the ternary mixture of R-290 + R-600a + R-32. Based on the experimental data, the VLEs for three binary mixtures were correlated by using the cubic equations of state with the conventional mixing rule, and the appropriate binary interaction parameters were determined for each binary mixture. For the R-290 + R-600a and R-32 + R-290 mixtures, the correlations were successful. For the R-32 + R-600a mixture, however, because of a relatively high nonideality, the accuracy of correlation was less than that for the other two mixtures. By applying the mixing rule based on the excess Gibbs free energy model, the accuracy was well improved. Moreover, by using the binary interaction parameters for each binary mixture the prediction of the VLE for the R-290 + R-600a + R-32 mixture was tested, and predicted bubble-point pressures were compared with the experimental values. The accuracy of this prediction was at similar level to the VLE correlation for the R-32 + R-600a mixture.