Asymptotic properties of radial A plus B → C reaction fronts

If two initially separated solutions of reactants are put in contact and a simple A + B -> C reaction takes place, reaction-diffusion profiles develop due to the coupling of reaction and diffusion. The properties of such fronts are well known in the case of an initially planar contact line between the two solutions. In this study one of the reactants is injected at a constant flux from a point source into a miscible solution of the other reactant so that the reaction front expands out radially. Both the leading order large-time and small-time asymptotic limits of the reactant concentrations and reaction front position are obtained analytically. Just as in the planar reaction front case, the position of the reaction front scales like t(1/2) and the width of the reaction front scales with t(1/6). In the large Peclet number limit the large-time asymptotic properties of the radial reaction front are found to be similar to those of the planar front except that the profiles are advected with the fluid flow. The distance between the contact line and the position of the radial reaction front is 1/root 2 of the distance that a planar reaction front travels. Further, the length scales inside and outside of the reaction zone are reduced by factors of 2(1/6) and root 2, respectively, compared to the planar reaction front.