Measuring stretching to predict the progress of diffusively limited chemical reactions

We investigate an acid-base reaction in the presence of chaotic advection and diffusion using experimentally measured stretching fields and fluorescent monitoring of the product. Both the flow symmetry and the Reynolds number (\textit{Re}) affect the spatial distribution and time dependence of the reaction product, which grows more slowly than expected, possibly as a result of highly non-uniform stretching.~ A single parameter, the product of the mean Lyapunov exponent $\bar {\lambda }$ and the number of cycles $N$, can be used to predict the spatial average time-dependent product concentration for flows possessing different degrees of spatial symmetry and various \textit{Re}. Unexpected oscillations occur on a time-scale much slower than the basic flow period, a phenomenon that is not reproduced by the usual model for fast reactions.~ This work was supported by National Science Foundation grant DMR-0405187.