Vapor-liquid critical surface of ternary difluoromethane+pentafluoroethane+1,1,1,2-tetrafluoroethane (R-32/125/134a) mixtures

The plane of vapor-liquid criticality for ternary refrigerant mixtures of difluoromethane (R-32)+pentafluoroethane (R-125)+1,1,1,2-tetrafluoroethane (R-134a) was determined from data on the vapor-liquid coexistence curve near the mixture critical points. The compositions (mass percentage) of the mixtures studied were 23% R-32+25% R-125+52% R-134a (R-407C), 25% R-32+15% R-125+60% R-134a (R-407E), and 20% R-32+40% R-125+40% R-134a (R-407A). The critical temperature of each mixture was determined by observation of the disappearance of the meniscus. The critical density of each mixture was determined on the basis of meniscus disappearance level and the intensity of the critical opalescence. The uncertainties of the temperature, density, and composition measurements are estimated as ±10 mK, ±5 kg·m^-3, and ±0.05%, respectively. In addition, predictive methods for the critical parameters of R-32/125/134a mixtures are discussed.