Vapor–Liquid-Equilibrium (VLE) properties of R-32+R-134a system derived from isochoric measurements

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Two methods developed for deriving Vapor–Liquid-Equilibrium (VLE) data from isochoric measurements are presented in this paper. The first, so-called `flash' method depends on a knowledge of the volumetric properties, estimated by means of an appropriate model; in the present case, the Carnahan–Starling–De Santis (CSD) equation of state (EOS) was used to predict the mixture's behavior. As for the second, so-called `model-free' method, the first step is based on dew point evaluation by interpolating experimental P–T sequences. The dew point value obtained is then used to derive VLE data, again using the Carnahan–Starling–De Santis equation of state. Two hundred twenty-five experimental P–V–T–x experimental data were obtained using a constant volume apparatus and 12 different binary mixture compositions prepared with the halogenated refrigerants difluoromethane (R-32) and 1,1,1,2-terafluoromethane (R-134a}, in a temperature range of 240–360 K. From these experimental data the VLE properties were derived by using the two methods. A comparison of the results obtained against data in the literature shows consistent agreement within the experimental uncertainty.