Notes on Stefan-Maxwell equation versus Graham's diffusion law

Certain prerequisite information on the component fluxes is necessary for s olution of the Stefan-Maxwell equation in multicomponent diffusion systems and the Graham's law of diffusion and effusion is often resorted for this p urpose. This article addresses solution of the Stefan-Maxwell equation in b inary gas systems and explores the necessary conditions for definite soluti on of concentration profiles and pertinent component fluxes. It is found th at there are multiple solutions for component fluxes in contradiction to wh at specified by the Graham's law of diffusion. The theorem of minimum entro py production in the non-equilibrium thermodynamics is believed instructive in determining the stable steady state solution out of infinite multiple s olutions possible under the specified conditions. It is suggested that only when the boundary condition of component concentration is symmetrical in a n isothermal binary system, the counter-diffusion becomes equimolar. The Gr aham's law of diffusion seems not generally valid for the case of isotherma l ordinary diffusion.