This method (PRH) is a modification of the Peng-Robinson mixing rule designed to improve the predicted phase behavior of strongly non-ideal mixtures. Huron and Vidal developed a relationship between the mixing rule and excess Gibbs free energy such that the infinite pressure Gibbs free energy could be expressed by a NRTL liquid activity coefficient method. By regressing experimental data to obtain the parameters for the modified NRTL expression, excellent vapor-liquid equilibria representation is possible for many systems.
The PRH method in PRO/II uses an improved alpha correlation developed by SimSci. The improved correlation provides more accurate vapor pressure predictions than the original PR formulation for a wide range of components.
In addition to K-values, the PRH equation may be used to predict the enthalpies, entropies and densities for the liquid and vapor phases. The predicted liquid phase densities are not very accurate and the API method is selected by default when the PRH system is chosen.
See "Soave-Redlich-KwongHuron-Vidal (SRKH) and Peng-Robinson Huron-Vidal (PRH)" under "Equations of State" in Chapter 2, Volume 1, of the PRO/II Reference Manual for more information.
Application Guidelines
Specific systems for which the Huron-Vidal parameters are available or can be determined by regressing experimental data.