2-FLUID CORRESPONDING STATES MODEL - A NEW MIXING RULE APPROXIMATION

A semi-empirical approximation of the generalised Percus-Yevick (PY) e quation for a mixture of hard spheres by Lebowitz (1964) is used to im prove the representation of the thermodynamic properties of dense flui d mixtures. The radial distribution function obtained by Lebowitz has been used to derive mixing rules in which a difference of the size of the constituent molecules has a direct effect. The performance of the new approximation is illustrated by comparing the results obtained fro m it with those from two earlier models for fluid mixtures with differ ent molecular sizes within the framework of the principle of correspon ding states. In order to separate the examination of the effect of cha nges in the mixing rules from the effects of uncertainties in the pair potential for real fluids, the tests conducted here make use of the r esults of computer simulation for prescribed and simple intermolecular potential models.