In many papers reporting models of adsorption processes, for historical reasons, the axial dispersion term is often either written in an incorrect form or the boundary conditions applied are not consistent. We review the correct formulation of these terms and show why the Danckwerts boundary inlet condition should be used in preference to the assigned inlet concentration. We also present a new formal proof of the exit boundary condition for open-closed systems and extend the results to open-open systems, which are practically relevant when solving adsorption models using finite element numerical schemes.

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