Buoyancy-driven convection may switch between reactive states in three-dimensional chemical waves

Abstract

Traveling waves in an extended reactor, whose width cannot be neglected, represent a three-dimensional (3D) reaction-diffusion-convection system. We investigate the effects of buoyancy-driven convection in such a setting. The 3D waves traveled through horizontal layers of the iodate-arsenous acid (IAA) reaction solution containing excess of arsenous acid. The depth of the reaction solution was the examined parameter. An increase in the intensity of buoyancy-driven flow caused an increase of the traveling wave velocities. Convection distorted the front of the chemical waves. For layers deeper than h>13 mm, heat release became smaller than heat production causing the emergence of Rayleigh-Bénard convection cells. At the interface, a dependency of wave shape on solution depth was observed. For h<7 mm, the waves adopted a stable V-like shape, while for h>13 mm a parabolic shape dominated. For 7<h<13 mm, both shapes were realized with the same probability. Finally, an intermittent switch between stoichiometric regimes is observed as an unexpected effect of the buoyancy-driven convection. The switch is expressed by iodine enrichment in the product. Hence, the experiments demonstrate that the buoyancy-driven convective flow can cause long-lived, but nevertheless transient, changes in the chemical composition by inducing a local transition between different regimes of the IAA reaction.

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

“…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.…”

“…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. 47 On the other hand, the opposite limit case of pure Marangoni flows affecting the propagation of chemical fronts in the absence of density changes has been relatively less investigated except for the case of surface reactions. 48,49 In the particular case of the Belousov-Zhabotinskii (BZ) reaction, numerical integrations of the Oregonator model equations coupled to the Navier-Stokes equations have allowed the comparison between Marangoni and buoyancy-driven effects on the dynamics of pulse waves.…”

Convection induced by thermal gradients on thin reaction fronts

“…Examples of these fronts can be found in combustion where chemical reactions are exothermic [3]. Compositional and thermal gradients lead to convection in polymerization fronts [4], and also in autocatalytic chemical reactions propagating in liquids such as the iron(II)-nitric acid reaction [5], the iodate-sulfite reaction [6], the chlorite-tetrathionate reaction [7][8][9], and the iodate-arsenous acid (IAA) reaction [10].…”

Diffúzív és konvektív instabilitás tanulmányozása autokatalitikus reakciófrontokban

“…A rendelkezésre álló térnek megfelelően különböző nagyságú, de azonos nyílási szögű V formájú minták keletkeztek a reakció lejátszódása során. Hasonló mintázatok létrejöttét tapasztalták más kutatók is, akik szintén a háromdimenziós hullám vízszintes terjedését vizsgálták, de a jodát-arzénessav rendszerben az oldatréteg magasságának változtatásával [95]. A növekvő cellaszélességnél kapott frontsebességek értékeit összehasonlítva az látható, hogy nem térnek el jelentős mértékben egymástól, közel azonosnak mondhatók.…”