In many technical processes gas multicomponent diffusion takes place in confinements that are rarely uniform in direction of their long axis (e.g., catalysts pores). Here we show that in conical tubes multicomponent diffusion is hindered. This effect increases with ratio of inlet to outlet cone radius Λ, indifferent of the orientation of the tube. Based on the Maxwell-Stefan equations we developed a predictive analytical solution for ideal multicomponent diffusion in slightly tapered ducts. (1962) were reproduced. Comparison of model and experiment shows that the solution presented here provides a reliable quantitative prediction of the temporal change of H 2 , N 2 , and CO 2 -concentration for both tube geometries, uniform and slightly conical. In the demonstrated case (Λ = 3.16) mass diffusion is 68 % delayed. Thus, for gaseous diffusion in "real", typically tapered pores the transport limitation is more serious than considered so far.
In Two Bulb Diffusion Experiments on a uniform tube the results of Duncan and Toor