MODEL OF EFFECTIVE KINETIC MOLECULAR DIAMETER FOR CALCULATING PROPERTIES OF DENSE FLUIDS

A procedure is proposed for determining effective molecular sizes nece ssary for the description of properties of real materials within the E nskog theory developed for a hard-sphere model. A nonempirical method is suggested for determining the effective molecular diameter sigma(ef f), taking into account the screening effect of the fields induced by surrounding particles on the pair-interaction potential. This method h elps establish the dependence of the effective diameter both on temper ature and on the medium density and produce an adequate description of properties of real materials in the entire range of density values fr om rarefied gas (b rho --> 0) to liquid on the solidification line (b rho --> 2). In both limiting cases, the sigma(eff) values agree with t he data of the molecular-kinetic theory of rarefied gases, perturbatio n theory, and the data provided by the equation of state for dense gas es. In the calculations, the Lennard-Jones model potential is used, bu t the results obtained may also be extended to any other real model of the interaction potential.