Calculation of the diffusion coefficient of dilute gases and of the self-diffusion coefficient of dense gases



A corresponding-states correlation of low-density binary- and self-diffusion coefficients is presented. The equations are simple to use, are sufficiently accurate for most calculations, and correlate those data used in their derivation somewhat better than calculations based on the Lennard-Jones potential if potential parameters have to be estimated from the critical properties. The Enskog kinetic theory of dense gases is used in modified form to obtain an expression for the high-density diffusion coefficient for isotopic mixtures in terms of the viscosity and compressibility of the gas. Generalized viscosity and compressibility charts are then used to construct a graph for predicting a reduced self-diffusion coefficient as a function of reduced temperature Tr = T/Tc and reduced pressure pr = p/pc. The effect of the pressure on the Schmidt number, Sc = μ/ρ��, is also discussed. Finally the extension of this chart to nonisotopic mixtures is considered.