Lock exchange and autocatalytic reaction front

Lab FAST, UPMC Paris6 UPS Paris11 and CNRS, Bat. 502, Orsay, F-91405, France. Viscous lock-exchange is the reciprocal exchange of two fluids of different density in a horizontal channel: the front between the two fluids spreads as the square root of time with a diffusion coefficient reflecting the buoyancy, viscosity and geometry of the current. Iodate Arsenous Acid (IAA) autocatalytic reaction front between reactant and product propagates as solitary waves (constant velocity and stationary concentration profile) resulting from a balance between molecular diffusion and chemical reaction. The fluid left behind the front has a different density leading to a lock-exchange configuration. We revisit, with chemical reaction, the lock exchange situation. We present an experimental analysis of buoyancy effects on IAA reaction fronts, propagating in horizontal rectangular channels of different aspect ratio. We observe stationary-shaped fronts, spanning the height of the cell and propagating along the cell axis. As the result of the data analysis, we find out that the product of the front velocity times its extension is nothing but the diffusion coefficient of the lock-exchange in the absence of chemical reaction. The analysis accounts for results in other geometries and for other chemical reactions.