Simulation was used to study self-diffusion in pure supercritical fluid, and Maxwell-Stefan mutual diffusion in binary supercritical Ar-Kr solutions. In the supercritical fluid, the temperature dependence of the self-diffusion coefficient obeyed an Arrhenius relationship quite well, and the calculated activation energy decreased with increasing density. In the binary supercritical Ar-Kr solution, the concentration dependences of both self-diffusion and Maxwell-Stefan mutual diffusion coefficients were obtained. The self-diffusion coefficients of Ar and Kr increased with increasing molar fraction of Ar. The calculated Maxwell-Stefan diffusion coefficients were larger than those predicted by the Darken relationship. The results also showed that the velocity cross-correlation was not negligible, and positive. This system could not be treated as an ideal system, and was different from Ar-Kr solution in the normal state where the Darken relationship was applicable.

Molecular Dynamics Simulation on the Inter-Diffusion of Supercritical Lennard-Jones (L-J) Mixture. Ge, S., Chen, M.: Chemical Journal of Chinese Universities, 2011, 32[11], 2593-7