Parallel-competitive reactions in a two-dimensional chaotic flow

A parallel-competitive reaction system, A + B-1 --> 2P and A + B-2 --> 2W, where A and B-1 are the reactants, B-2 is a reactive impurity, P is the des ired product, and W is a byproduct, is simulated in a chaotic flow by solvi ng the differential convection-diffusion-reaction equations. Three differen t flow conditions are investigated: a predominantly regular system, a globa lly chaotic flow, and an intermediate case that displays predominantly chao tic behavior but which has four small islands of regular flow. The time evo lution and spatial distribution of species concentration depend strongly bo th on the nature of the flow and on the relative rates of the two reactions . Even in the globally chaotic flow, significant spatial heterogeneity exis ts throughout the duration of the reactive mixing simulation. Product and w aste accumulate in different spatial regions, depending on the relative cha racteristic times of the two reactions. When the primary reaction is the fa ster one, waste tends to accumulate in local A-rich regions and the selecti vity of product to waste is strongly affected by the degree of chaos in the system. On the other hand, when the side reaction is faster, waste accumul ates in segregated regions which have local excesses of B-2, but mixing has minimal effect on the quantity of waste produced. (C) 1999 Elsevier Scienc e Ltd. All rights reserved.