Velocity profiles and circulation in Stefan-diffusion

Recently, a new multicomponent fluid transport theory was presented by Kerkhof and Geboers [2005a. Towards a unified theory of isotropic molecular transport phenomena. A.I.Ch.E. Journal 51, 79–121], in which the transport is described by simultaneous equations of motion for each species. The theory is applied to water vapor and nitrogen in the Stefan tube as an example of two-dimensional fluid transport. Numerical solution results in axial and radial velocity profiles for both species and clearly indicates circulation of nitrogen. Comparison with the classic Stefan-diffusion equation shows that for wide tubes the latter approach is still reasonable, but for narrow tubes shear effects dominate. The nitrogen circulation causes radial concentration profiles. For small diameter tubes, the axial velocity profiles from the present model are close to those from the velocity profile model of Kerkhof et al. [2001. On the isothermal binary transport in a single pore. Chemical Engineering Journal 83, 107–121], in which radial transport was assumed to be infinitely fast.