Prediction of Phase Equilibria for Refrigerant Mixtures of Difluoromethane (HFC-32), 1,1,1,2-Tetrafluoroethane (HFC-134a), and Pentafluoroethane (HFC-125a) Using SAFT-VR

The statistical associating fluid theory for chain molecules with attractive potentials of variable range (SAFT-VR) is used to model the phase equilibria for three binary mixtures formed by difluoromethane (HFC-32), 1,1,1,2-tetrafluoroethane (HFC-134a), and pentafluoroethane (HFC-125a). Molecules are represented as chains of spherical segments with short-ranged attractive sites. The intermolecular van der Waals forces are modeled with variable-range square-wells. The optimized values of the parameters of the model are obtained by fitting to experimental data for the vapor pressures and saturated liquid densities of each of the pure components. These parameters are the number and diameters of the spherical segments and the strengths and ranges of the potentials describing the site−site and segment−segment interactions. Using the values of the pure-component parameters and standard combining rules, the phase equilibrium of the mixtures is described very accurately. SAFT-VR improves the predictive power of mean-field versions of SAFT.