Estimating the self-diffusion coefficients and mutual diffusion of binary mixtures on the basis of modified van der Waals model

The previously proposed model is used to determine the values of the self-diffusion coefficient of He, Ne, Ar, Kr, Xe, H$_2$, D$_2$, N$_2$, O$_2$, CO$_2$, NH$_3$, and CH$_4$ in the liquid and dense gaseous states, which were compared with the experimental data obtained at a pressure of $\approx$200 MPa and a temperature of $\approx$500 K. The calculations are carried out with the use of the equation of state of these substances in the form of a modified van der Waals model. The self-diffusion model was generalized for the case of mutual diffusion in binary mixtures, which is based on the modified model of the van der Waals state equation for mixtures. The modeled coefficient of mutual diffusion for a great number of binary mixtures of the above-mentioned individual substances is determined, and the results are compared with the known data. Without special calibration for the experiment, the model correctly predicts the relationship of the self-diffusion and mutual diffusion coefficients (with their variation by several orders of magnitude in the case where the density changes from gaseous to liquid) with both pressure and temperature. For most substances considered in the paper, the maximum deviations of calculations from the experiment do not exceed 30–50%.