Abstract: Certain prerequisite information on the component fluxes is necessary for solution of the
Stefan-Maxwell equation in multicomponent diffusion systems and the Graham’s law of
diffusion and effusion is often resorted for this purpose. This article addresses solution
of the Stefan-Maxwell equation in binary gas systems and explores the necessary conditions
for definite solution of concentration profiles and pertinent component fluxes. It is found
that there are multiple solutions for component fluxes in contradiction to what specified
by the Graham’s law of diffusion. The theorem of minimum entropy production in the non-
equilibrium thermodynamics is believed instructive in determining the stable steady state
solution out of infinite multiple solutions possible under the specified conditions. It is
suggested that only when the boundary condition of component concentration is symmetrical
in an isothermal binary system, the counter-diffusion becomes equimolar. The Graham’s law
of diffusion seems not generally valid for the case of isothermal ordinary diffusion.

Key words: ordinary diffusion, Stefan-Maxwell equation, Graham's law of diffusion, theorem of minimum entropy production, nonequilibrium thermodynamics

摘要： Certain prerequisite information on the component fluxes is necessary for solution of the
Stefan-Maxwell equation in multicomponent diffusion systems and the Graham’s law of
diffusion and effusion is often resorted for this purpose. This article addresses solution
of the Stefan-Maxwell equation in binary gas systems and explores the necessary conditions
for definite solution of concentration profiles and pertinent component fluxes. It is found
that there are multiple solutions for component fluxes in contradiction to what specified
by the Graham’s law of diffusion. The theorem of minimum entropy production in the non-
equilibrium thermodynamics is believed instructive in determining the stable steady state
solution out of infinite multiple solutions possible under the specified conditions. It is
suggested that only when the boundary condition of component concentration is symmetrical
in an isothermal binary system, the counter-diffusion becomes equimolar. The Graham’s law
of diffusion seems not generally valid for the case of isothermal ordinary diffusion.

关键词: ordinary diffusion;Stefan-Maxwell equation;Graham's law of diffusion;theorem of minimum entropy production;nonequilibrium thermodynamics