Vapor-liquid equilibrium measurements of HFO refrigerant mixtures.

Hydro-fluoro-olefins (HFOs) and their mixtures are expected to be the alternatives of hydro-fluorocarbons (HFCs) as low global warming potential (GWP) refrigerants. Vapor-liquid equilibrium (VLE) data of HFO mixtures are highly required for the development of mixture models of equations of state. In this study, a recirculation method is adopted for the VLE measurement of refrigerant mixtures including HFOs such as R1123 and R1234yf. The apparatus mainly consists of an equilibrium cell having optical windows, circulation pumps, and a gas chromatograph. A sample is filled in the equilibrium cell at a VLE condition, and the compositions of vapor and liquid phases sampled through hexagon valves are determined by the gas chromatograph. The apparatus has been modified by improving the position of a pressure transducer to be immersed in a thermostatic bath. Vapor pressure of R1234yf was measured as confirmation of the performance of the apparatus, and the obtained data are compared with an equation of state.