A theory-based method for correlation and prediction of dense-fluid transport properties

Dense-fluid transport property data for a wide range of compounds have been successfully correlated on the basis of universal curves for the reduced diffusion coefficient,D ^*, the reduced viscosity, η^* and the reduced thermal conductivity, λ^*, against the reduced volumeV/V _o , whereV is the molar volume, andV _o is a characteristic volume equal to the volume of close packing for a system of hard spheres. The reduced transport properties,X ^*, are defined in terms of the low-density hard-sphere values by (X/X _o )(V/V _o )^2–3, whereX is ν, λ, or the product of the number density and the diffusion coefficient. To provide a theoretical justification for this approach, extensive computer simulation results for these transport properties, given in the literature for a system of Lennard-Jones (12–6) molecules, have been considered. It is found that the reduced transport properties for different temperatures are superimposable upon the results for any reference isotherm when plotted versus logV, as found previously for real fluids. However, to reproduce this density dependence at any given temperature on the basis of the universal curves, the characteristic volume for self-diffusion must be greater than that for viscosity or thermal conductivity. Invited paper presented at the Fourth Asian Thermophysical Properties Conference, September 5–8, 1995, Tokyo, Japan.