Isothermal VLE Measurements for the Binary Mixtures HFC-134a+HFC-245fa and HC-600a+HFC-245fa

The substitution of CFC-114 in high temperature heat pumps is still far from being solved. Some pure compounds such as 1,1,1,2,3,3-hexafluoropropane (HFC-236ea), 1,1,1,3,3,3-hexafluoropropane (HFC-236fa) and 1,1,1,3,3-pentafluoropropane (HFC-245fa) have been proposed, but it is probable that the best alternative will be given by a binary or ternary mixture including one of these fluids. The experimental data on the thermodynamic properties of these fluids are still scarce and, for mixtures, the evaluation of vapor-liquid equilibrium (VLE) behavior is crucial. This paper presents the measurement of isothermal VLE p-T-x-y data of the two binary refrigerant systems 1,1,1,2-tetrafluoroethane (HFC-134a)+HFC-245fa and isobutane (HC-600a)+HFC-245fa at three temperatures ranging from 293.15 to 313.15 K. The measurements are performed by means of an apparatus based on the recirculation of vapor into liquid and the gas chromatographic analysis of the compositions. The estimated accuracies of measured data are ±0.02 K for temperature, ±1 kPa for pressure, ±0.002 in mole fraction for liquid composition and ±0.003 in mole fraction for vapor composition. The VLE data are correlated with the RKS equation of state in connection with the Huron-Vidal mixing rules. Very good agreement between the experimental and the calculated data is obtained.