New equations of state for pure and binary hard-sphere fluids

An equation of state for one-component fluids of hard spheres is proposed. The equation has the form of the Pade′ approximant of the rescaled virial series and uses the first seven virial coefficients. The equation is superior to the Carnahan–Starling, the Erpenbeck–Wood and the Kolafa equations of state. It is shown that its accuracy is almost the same as the precision of recent simulation data. The same general form of the equation is used for binary additive mixtures of hard spheres. The equation utilizes known virial coefficients up to the fifth as functions of the mole fraction and the sphere diameter ratio. Comparisons with Monte Carlo computer simulation data show that the equation is more accurate than the Boublik–Mansoori–Carnahan–Starling–Leland and similar equations of state at fluid packing fractions up to η=0.49. Possible extensions and applications of the proposed equations are discussed.