Phase equilibrium in a special class of polydisperse fluid models.

For a special class of polydisperse fluid models we have developed methods for obtaining (numerically) exact solutions to the equilibrium conditions. The models considered are special in the sense that the functional dependence of thermodynamic properties on the mole–fraction distribution density F(I) and microscopic parameter functions is restricted. For example, the pressure may depend only on a single moment of F(I). For our special class of models, we show how the dew/bubble conditions can be given a simple two-dimensional geometric representation, and the dew/bubble conditions are reduced to solving two equations in two unknowns. The solution of the full equilibrium conditions can be obtained by an iterative procedure given the solutions of the dew/bubble equations. Three specific models, based on the van der Waals and Soave–Redlich–Kwong equations of state, are examined in detail. We also show how to implement these new solution techniques when the mixture contains a finite number of chemical species. [ABSTRACT FROM AUTHOR]