CONVECTIVE EFFECTS ON CHEMICAL WAVES .2. SIMPLE CONVECTION IN THE IODATE ARSENIOUS ACID SYSTEM

The convection-induced increase of the wave front velocity in the iodate-arsenous acid system can be explained by considering the convective flow velocity caused by the density gradient in the reaction front. The density is decreased by the exothermicity of the reaction and by the positive volume change of the reaction. Because both effects decrease the density, no complicated mechanism such as double-diffusive convection need be invoked. The wave front velocity may be considered as a superposition of a fluid flow velocity on a reaction-diffusion velocity. We provide a qualitative description of the upward and downward propagating fronts and make predictions of changes in the shape of the upward front at different tube radii. We calculate the increase in front velocity for ascending fronts using results from experiments on flames in vertical tubes. We also calculate the increase in front velocity for waves in a horizontal tube using an asymptotic solution for the fluid velocity in a differentially heated cylinder.