Some properties of the GHC equation of state

Abstract

Abstract The composition functionality of the mixture energy parameter, a M , used in the Gibbs-Helmholtz Constrained (GHC) equation of state is studied. An analysis is presented that shows that a M for liquid mixtures is approximately quadratic in composition. All non-quadratic behavior is due solely to ln(T cM ) in the GHC up-scaling equation. If a mean value approximation of this term is used, then a M L is quadratic, but non-symmetric, in composition. For vapors, non-quadratic behavior is coupled to the molar volume of the mixture through the term β M = (V M + b M )/V M . It is shown that the difference between β M and some average βM is very small and a M V is quadratic in composition. Sensitivity analyses of a M and resulting molar density to these approximations are also presented. Finally, the non-symmetric composition functionality of a M is discussed along with GHC predictions of mixture second virial coefficients. Numerical examples are presented to support all claims.