Dielectric constants of fluid mixtures over a wide range of temperature and density

A new expression is presented for estimating the dielectric constant of a fluid mixture as a function of temperature, density and composition. The estimated dielectric constants (and their derivatives) are required for phase-equilibrium calculations, based on an equation of state, for systems containing electrolytes and nonelectrolytes. The new expression holds for the entire range of fluid densities, from zero to liquid-like densities. Mixing of components is performed on a volume-fraction basis at constant temperature and constant reduced density. For polar components where data are not available at the temperature and/or reduced density of interest, the well-characterized behavior of water is used to extrapolate the available pure-component data. The importance of using the correct density of the mixture is shown. Using one adjustable parameter for each nonideal binary subsystem, predicted results can be significantly improved.