Effects of Fluid Flow on Chemical Excitation Waves with Normal and Anomalous Dispersion Relations

Reaction-Diffusion (RD) waves are autocatalytic reaction zones that propagate via molecular diffusion without mass transport. They arise from the interplay of nonlinear reaction kinetics of an activator and an inhibitor species and diffusion-mediated spatial coupling (e.g., action potentials in nerves, forest fires, or stadium waves). Introducing fluid flow in a liquid chemical RD system has a huge effect on the propagation behavior of the wave. By using glass capillary tubes to create a quasi-1D system, it is possible to develop stationary waves by advecting the liquid solution opposite to the direction of wave propagation. This occurs when fluid flow velocity is equal and opposite to diffusion. In our experiments, we used the Belousov-Zhabotinsky reaction with monotonic increasing (typical) and non-monotonic (anomalous) speed-wavelength relationships. After initiating waves at one end of a capillary, the reaction solution was advected in the opposite direction. The effect of flow rate on i) the propagation speed and ii) the front shape was investigated. We also present stationary chemical waves observed in both systems and report on the effect of advection on different types of anomalous wave dispersion.