Lock-exchange experiments with an autocatalytic reaction front

Abstract

A viscous lock-exchange gravity current corresponds to the reciprocal exchange of two fluids of different densities in a horizontal channel. The resulting front between the two fluids spreads as the square root of time, with a diffusion coefficient reflecting the buoyancy, viscosity, and geometrical configuration of the current. On the other hand, an autocatalytic reaction front between a reactant and a product may propagate as a solitary wave, namely, at a constant velocity and with a stationary concentration profile, resulting from the balance between molecular diffusion and chemical reaction. In most systems, the fluid left behind the front has a different density leading to a lock-exchange configuration. We revisit, with a chemical reaction, the classical situation of lock-exchange. We present an experimental analysis of buoyancy effects on the shape and the velocity of the iodate arsenous acid autocatalytic reaction fronts, propagating in horizontal rectangular channels and for a wide range of aspect ratios (1/3 to 20) and cylindrical tubes. We do observe stationary-shaped fronts, spanning the height of the cell and propagating along the cell axis. Our data support the contention that the front velocity and its extension are linked to each other and that their variations scale with a single variable involving the diffusion coefficient of the lock-exchange in the absence of chemical reaction. This analysis is supported by results obtained with lattice Bathnagar-Gross-Krook (BGK) simulations Jarrige et al. [Phys. Rev. E 81, 06631 (2010)], in other geometries (like in 2D simulations by Rongy et al. [J. Chem. Phys. 127, 114710 (2007)] and experiments in cylindrical tubes by Pojman et al. [J. Phys. Chem. 95, 1299 (1991)]), and for another chemical reaction Schuszter et al. [Phys. Rev. E 79, 016216 (2009)].

Marangoni-driven convection around exothermic autocatalytic chemical fronts in free-surface solution layers

“…In closed horizontal solution layers (no surface open to air), convection triggered by the density jump across a propagating front has been shown both experimentally [30][31][32][33][34] and numerically [35][36][37][38][39][40][41] to deform and to speed up this front in isothermal conditions. When the reaction is exothermic, the combination of solutal and thermal density changes comes into play and has been noted to affect for instance the propagation of polymerization fronts in horizontal layers 42,43 and to result in new dynamical behaviors for the case of chemical fronts of the chlorite-tetrathionate (CT) reaction [44][45][46] and of the IAA reaction.…”

“…54) but, as mentioned earlier, convection can affect the dynamics and propagation speeds of these fronts in aqueous solutions. 9,19,20,27,33,41,47,52 As discussed above, the complexity of such experimental systems arises from the fact that it is not always trivial to discriminate between surface tension-driven and buoyancy-driven convection.…”

Accurate measurement of curvilinear shapes by Virtual Image Correlation

“…According to the beam theory [8], the curvature is of importance as it is related to the bending moment. In fluid mechanics [9][10][11][12], or chemistry, the line to be identified can be a front (temperature, concentration...). In this case, the knowledge of the normal vectors, related to the angles of tangents, can be needed for a flux computation.…”

Diffúzív és konvektív instabilitás tanulmányozása autokatalitikus reakciófrontokban

“…Térgeometriai megfontolások figyelembevéte-lével hasonló következtetésre jutottak külföldi kutatók is, akik mind az elmélet, mind pedig kísérlet oldaláról megvizsgálták a közegmozgás hatását. Megállapították, hogy a folyadék magasságától függő keveredési hosszt nagyban befolyásolják a reakciókörülmények, és így mind a négyzetes arányosság, mind az 1,32-es hatványkitevő is érvényes lesz, csak más-más körülmények alkalmazása esetén [91,93,94].…”

“…A poli(vinil-alkohol) (PVA) koncentrációja a reaktánselegyben 1,2 g l −1 volt. Már korábban sikerült Salinnak és munkatársainak állandó sebességgel terjedő állandó alakzatokat létrehozni PVA alkalmazásával [91]. A létrejött frontalakjaim megegyeztek a náluk tapasztalható frontalakokkal azonos cella orientációnál.…”