Reaction enhancement of isolated scalars by vortex stirring

The effect of vortex stirring on reaction rate enhancement is investigated for two reactive scalars initially separated by a third nonreactive scalar. The presence of the intervening scalar precludes reactions at early times. Vortex stirring accelerates the coalescence of the reactive scalars relative to pure diffusion and enhances the resulting reaction rates. Analytical and numerical results for reactive stirring by a single point vortex are shown for a range of Peclet (Pe) and Damkohler (Da) numbers. At low Da and high Pe, nondimensional reaction rates grow as Pe(1/3), and peak reaction times decrease as Pe(-2/3). Reaction rates scale linearly with Da for slow reactions, but this scaling breaks down for fast reactions due to reactant depletion. The stirring-induced reaction rate enhancement is shown to be relatively insensitive to initial placement of scalars within the point vortex. The study provides mechanistic insights into more general mixing and reaction problems involving initially isolated scalars. (c) American Institute of Physics.