Convective fingering of an autocatalytic reaction front

Abstract

We report experimental observations of the convection-driven fingering instability of an iodate-arsenous acid chemical reaction front. The front propagated upward in a vertical slab; the thickness of the slab was varied to control the degree of instability. We observed the onset and subsequent nonlinear evolution of the fingers, which were made visible by a pH indicator. We measured the spacing of the fingers during their initial stages and compared this to the wavelength of the fastest growing linear mode predicted by the stability analysis of Huang et. al. [Phys. Rev. E, 48, 4378 (1993), and unpublished].We find agreement with the thickness dependence predicted by the theory.Typeset using REVT E X 1

On the classification of buoyancy-driven chemo-hydrodynamic instabilities of chemical fronts

“…An autocatalytic reaction that has been the focus of several experimental studies on convection-driven deformation of fronts is the iodate-arsenous acid ͑IAA͒ system that features reactants that are heavier than the products such that ⌬ c Ͻ 0. 6,8,22,23,30,31 This reaction is exothermic as well ͑⌬ T Ͻ 0͒; hence, the solutal and thermal effects are cooperative for the IAA reaction. According to the model of Pojman and Epstein, 5 only simple convection is expected in that case; i.e., only IAA fronts ascending the gravity field should be unstable.…”

“…The first experiments were performed in capillary tubes and have addressed the influence of the radius of the tube or of the angle of orientation with respect to gravity on the onset of convection ͑characterized by one or two convection rolls͒ and on the speed of the front. [3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21] More recently, experiments in Hele-Shaw cells [21][22][23][24][25][26][27][28][29][30] and in a three-dimensional tank 31 have allowed investigation of the dynamics of more extended systems and of the stability of a wider spectrum of instability modes.…”

“…According to the model of Pojman and Epstein, 5 only simple convection is expected in that case; i.e., only IAA fronts ascending the gravity field should be unstable. Indeed, several experimental and theoretical works have focused on characterizing Rayleigh-Taylor induced deformation of ascending IAA fronts in capillary tubes, 6,8,[32][33][34][35][36] in Hele-Shaw cells, 22,23,30,[36][37][38][39][40][41][42]45 and in threedimensional tanks. 31 A similar situation occurs for combustion fronts for which cold liquid fuel reactants are converted into hot gas products.…”

Dispersion relations for the convective instability of an acidity front in Hele-Shaw cells

“…1 Recent experiments have analyzed such an instability in Hele-Shaw cells, [2][3][4][5][6][7][8][9] two planar glass plates of large lateral extent separated by a thin gap width. In such a geometry, the convective instability of the front induced by the unfavorable density stratification leads to a fingering of the front characterized by several wavelengths.…”

Miscible density fingering of chemical fronts in porous media: Nonlinear simulations

“…9 In miscible systems, chemical reactions are more prone to provide density differences that can drive buoyantly unstable situations as soon as a heavier fluid lies on top of a lighter one. Experimental evidence [10][11][12][13][14][15][16][17][18][19][20] and theoretical studies [20][21][22][23][24][25][26][27][28][29][30][31][32] on density driven instabilities have shown that the coupling between buoyancy driven flows and chemical reactions can strongly affect the properties of the fingering instability. The coupling with chemical reactions has been addressed mainly concerning the stability of planar fronts with regard to Rayleigh-Taylor fingering.…”