PREDICTION OF TRANSPORT-PROPERTIES FOR LENNARD-JONES FLUIDS AND THEIR BINARY-MIXTURES USING THE EFFECTIVE-DIAMETER HARD-SPHERE KINETIC-THEORY

We present a critical appraisal of the ability of effective diameter hard sphere theory to predict thermal conductivities and shear and bulk viscosities of fluids interacting through the Lennard-Jones potential. This method relies on the use of the kinetic theory of hard spheres and on state dependent effective diameters given by the equilibrium liquid state theory. Predictions using this method are compared with molecular dynamics data given by several authors for pure fluids in many states (65 states for the thermal conductivity, 105 for the shear viscosity, and 45 for the bulk viscosity). In the dense regime, this procedure makes predictions with an average global deviation of 37% for the shear viscosity, 32% for the bulk viscosity, and 10% for the thermal conductivity when a variational scheme is used to give the effective hard sphere diameters. In specific regions of the phase diagram, however, the predictions are much better. All other schemes give worse results, although shear viscosity in certain regions of the phase diagram (for this case we include the low density regions), is better predicted by one of the perturbative methods. For mixtures, we extend the effective diameter hard sphere theory to binary systems with the standard hard sphere cross interaction. In addition, we calculate the transport properties of mixtures using the equivalent one-fluid approximation. Comparisons are also made with molecular dynamics calculations previously reported in 10 states for mixtures. Our results are satisfactory, mainly when the one-fluid approximation is used.