A cubic equation of state for mixtures containing steam

Abstract

A cubic equation of state and combining rules for mixtures containing steam has been developed The equation is based on the earlier equations of Clausius, Martin and Kubic, and contains two temperature-dependent parameters, which give it enough flexibility to fit the residual properties of both steam and non-polar fluids with sufficient accuracy. Mixture properties are calculated using pseudo-critical parameters for steam and a single temperature-independent interaction parameter ξ in the combining rule T_c12=ξ(T_c1T_c2)^½. For mixtures such as steam–carbon dioxide, where there is a specific interaction between the unlike components, ξ must be obtained from cross-term second virial coefficients. Where there is no specific interaction ξ is given by ξ= 2(V_c1V_c2)^½V_c12^–1(I₁I₂)^½(I₁+I₂)^–1. The equation of state fits measurements of the excess molar enthalpy H^E_m of mixtures containing steam at pressures of 0.1–10 Mpa, at temperatures up to at least 700 K, and allows the calculation of (p, V_m, T) properties.