EQUATION OF STATE FOR PURE FLUIDS AND MIXTURES BASED ON A TRUNCATED VIRIAL EXPANSION

An accurate, yet simple, equation of state was developed for pure fluids ranging from nonpolar to H2O and their mixtures. The equation consists of a virial expansion truncated after the fourth virial coefficient and a closed-form term approximating higher coefficients. For nonpolar or weakly polar compounds, the equation is generalized using critical temperature, critical pressure, and acentric factor. Despite its simplicity, the equation represents the P-V-T and saturation properties of pure fluids with a very good accuracy, which is comparable to that of multiparameter, generalized BWR-type equations. For mixture calculations, mixing rules were formulated based on the rigorously known composition dependence of virial coefficients. The equation represents vapor-liquid, gas-gas and liquid-liquid equilibria, as well as volumetric properties of mixtures containing nonpolar components and/or water. Binary parameters can be generalized for series of mixtures containing a common component.