Applicability of the linearized theory of the Maxwell–Stefan equations

The present article aims for a better understanding of the applicability of the linearized theory of the Maxwell–Stefan equations for multi‐component diffusion. An analysis of the theory's accuracy is performed with respect to the classical two‐bulb diffusion experiments by Duncan and Toor, from which the results are transferred to more general scenarios. It is shown that for an accurate linearized theory it is essential to have a quasi‐stationary and quasi‐one‐dimensional flux, and also a so‐called reference point. Two examples illustrating the theory's failure in case of unmet prerequisites are presented: a three‐bulb configuration and a two‐dimensional diffusion case. For the first setup the linearized theory results in negative concentrations, for the second it requires influxes at openings that are actually outlets. © 2016 American Institute of Chemical Engineers AIChE J , 62: 2929–2946, 2016