P-V-T-x and vapor-liquid equilibrium properties of pentafluoroethane (R125)+1,1,1,3,3,3-hexafluoroethane (R236fa) and 1,1,1,2-tetrafluoroethane (R134a)+R236fa systems derived from isochoric measurements

P-V-T-x measurements were performed using a constant-volume apparatus for t he pentafluoroethane (R125) + 1,1,1,3,3,3-hexafluoropropane (R236fa) and 1, 1,1,2-tetrafluoroethane (R134a) + 1,1,1,3,3,3-hexafluoropropane (R236fa) sy stems, in a temperature range of (253-372) K and a pressure range of (113-2 360) kPa. Experimental data were collected on three different compositions for each of the systems. Eight expansion series with a total of 121 data po ints and nine expansion series with 110 data points were performed, respect ively, for the R125 + R236fa and R134a + R236fa systems, both within the va por-liquid equilibrium (VLE) boundary and in the superheated vapor region. The data in the superheated vapor region were interpreted using tried and t ested correlating methods for the second and third virial coefficients. The VLE parameters were derived by applying two methods: (1) The flash method enabled VLE parameters to be derived directly from P-V-T-z data within the VLE boundary by applying the Carnahan-Starling-De Santis (CSD) equation of state (EOS). (2) The dew-point method was based on dew-point evaluation by interpolating experimental P-T sequences. The resulting dew-point value was then used to derive VLE parameters, again using the CSD EOS. A comparison of the results emerging from these two methods, followed by the interpretat ion of the volumetric properties of the superheated vapor, confirmed their internal consistency.