Thermodynamic property models for the difluoromethane (R-32) + trans-1,3,3,3-tetrafluoropropene (R-1234ze(E)) and difluoromethane + 2,3,3,3-tetrafluoropropene (R-1234yf) mixtures

Thermodynamic property models explicit in the Helmholtz energy are presented for the R-32/1234ze(E) and R-32/1234yf mixtures. The Helmholtz energy of the mixtures are expressed as the sum of the ideal mixture contribution and the contribution from mixing. The independent variables are the temperature, molar volume, and composition. The most accurate pure-fluid equations of state are incorporated to calculate the ideal mixture contribution. The contribution from mixing is determined by fitting to available experimental data. The estimated uncertainties in calculated properties from the models are 1% for the bubble point pressure and 0.25% for liquid density. The critical loci of the mixtures are reasonably represented with the models. The calculated critical temperatures correspond to experimental values within ±0.8 K.