Applications of the Augmented van der Waals Theory of Fluids.: I. Pure Fluids

The relation for the compressibility of hard convex bodies (Boublik, 1975) is combined with the power series in (u/k T) and (V°/V) (Alder et al., 1972) to obtain the most general and accurate equation of state of fluids. 24 universal constants of the series were fitted to the internal energy and PVT data for argon. The equation also contains 5 characteristic constants that were fitted to the properties of 11 fluids to show its validity at all densities ranging from zero (second virial coefficients) to the liquid density at T/Tc = 0.55 that corresponds to the triple point of argon. The interaction energy u/k appears to be equal to the critical temperature Tc for small molecules but it becomes a function of the temperature for non-spherical molecules, in agreement with the theory of non-central forces.