Vapour-liquid equilibrium of ternary mixtures of the refrigerants R32, R125 and R134a

Ternary mixtures of R32, R125 and R134a of different compositions are recommended for replacing refrigerants R22 and R502. As a prerequisite for reliably calculating vapour pressure and phase equilibria of ternary mixtures within the relevant range of temperature and composition, VLE data of the three binary systems R32/R134a, R125/R134a and R32/R125 have been measured from -70 degrees C up to the critical temperature. The real mixing behaviour of these binary systems is described by simple cubic equations of state, based only on precise experimental data of the critical properties and one value of the vapour pressure at T/T-c approximate to 0.7 for one mixture of nearly equimolar composition, respectively. Besides the properties of the pure substances, these data are sufficient to calculate the saturation pressure as well as the composition of the coexisting phases with rather high accuracy for both the binary and the ternary mixtures. This has been proved by comparison with experimental data for binary mixtures and for three ternary mixtures of different compositions.