Diffusion creep

Diffusion creep refers to the phenomenon of flow on a surface along which is a concentration gradient. A number of well known mass transfer problems that have usually been analyzed ignoring diffusion creep are revisited, including isobaric and equimolar counterdiffusion, diffusion with one component stationary, and diffusion with surface reactions. The Kramers and Kistemaker model for the creep velocity is used as a benchmark, and the implications of more recent advanced kinetic theory analyses explored. The validity of Graham’s law for isobaric counterdiffusion is examined. The resulting phenomenon of diffusiophoresis of Stokesian particles is briefly discussed.