| Abstract
| - To gain a better understanding of the advection of reaction fronts in a porous medium, we consider thesimilarities and the differences between the advection of wavefronts in a packed bed and in a flat gap or apipe. The model calculations are based on the reaction−diffusion−advection equation for cubic autocatalysis,with the flow field in a gap taken into account explicitly. The analysis performed allows us to conclude that,in the “wide gap” limit, i.e., when the ratio of the gap (or pore) width to the front width is large, for theadverse flow in a porous medium one can expect the formation of stationary wavefronts for a wide range offlow velocities, if one takes into account that advection in a porous medium can effectively quench the axialdiffusion of an autocatalyst. These predictions are verified experimentally for a non-oscillatory autocatalyticreaction, viz., the oxidation of thiosulfate with chlorite, carried out in a packed bed of glass beads. It isdemonstrated for the first time that, in the case of an adverse flow, the stationary wavefronts in the “widegap” limit are indeed observed for this reaction, and this limit can be achieved by, e.g., increasing theconcentrations of the key reactants. We suggest that the observations of stationary wavefronts in the oscillatoryBelousov−Zhabotinsky reaction reported earlier can be accounted for in similar terms. The formation ofstationary wavefronts in a packed bed is favored owing to the much larger flow dispersion effects (the ratioof the largest flow velocity to the average flow velocity) in a porous medium as compared to flow in a gapor a pipe. Nevertheless, for a correct description of the effects of advection on the wavefront propagation, itis not appropriate to substitute the dispersion coefficient for diffusivity in the reaction−diffusion−advectionequation.
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