04-10E

Polydisperse multi-Yukawa hard-sphere fluid model is proposed and analytical description of its thermodynamical properties is developed using van der Waals (vdW) approximation and high temperature approximation (HTA). It is demonstated that in the frames of both approximations the model belongs to the class of the "truncatable free energy models", i.e. the models with thermodynamical properties (Helmholtz free energy, pressure, chemical potential) defined by the finite number of generalized moments. Using this property the complete phase diagram, including binodal curves and cloud and shadow curves, is calculated using vdW approximation. Analysis of our results and their comparison with corresponding results obtained earlier via mean spherical approximation (MSA) is carried out, which allows us to establish the limitations of vdW approach in polydisperse case.