The thermal diffusion factor for binary mixtures of hard spheres was calculated by a direct non-equilibrium molecular dynamics simulation method. The results obtained showed that for equimolar isotopic binary mixtures of hard spheres, the thermal diffusion factor increased with density at fixed mass ratios and increased with mass ratio at fixed packing fractions. The dependence of thermal diffusion factor upon diameter ratio was also investigated and it was found that if the mass ratio was equal to 1 then larger species were accumulated in the warm region. The reciprocal of the thermal diffusion factor as a function of the mole fraction of the heavier component in two packing fractions was studied as well. The results obtained showed that inverse of thermal diffusion factor 1/(thermal diffusion factor) tended to be more linear when the mass ratio significantly differed from 1 and the diameter ratio was close to 1. These results were in good agreement with revised Enskog theory. It was also found that those low density results continue to apply at higher densities too.

Non-Equilibrium Molecular Dynamics Calculation of Thermal Diffusion Factor in Binary Mixtures of Hard Spheres. Yeganegi, S., Zolfaghari, M.: Fluid Phase Equilibria, 2006, 243[1-2], 161-5