Differential diffusion effects on buoyancy-driven instabilities of acid-base fronts: the case of a color indicator.

Buoyancy-driven hydrodynamic instabilities of acid-base fronts are studied both experimentally and theoretically in the case where an aqueous solution of a strong acid is put above a denser aqueous solution of a color indicator in the gravity field. The neutralization reaction between the acid and the color indicator as well as their differential diffusion modifies the initially stable density profile in the system and can trigger convective motions both above and below the initial contact line. The type of patterns observed as well as their wavelength and the speed of the reaction front are shown to depend on the value of the initial concentrations of the acid and of the color indicator and on their ratio. A reaction-diffusion model based on charge balances and ion pair mobility explains how the instability scenarios change when the concentration of the reactants are varied.

[1]  K. Eckert,et al.  Convective mixing induced by acid-base reactions. , 2011, The journal of physical chemistry. B.

[2]  A. Wit,et al.  Buoyancy-driven instabilities of miscible two-layer stratifications in porous media and Hele-Shaw cells , 2010, Journal of Fluid Mechanics.

[3]  S. Backhaus,et al.  Convective instability and mass transport of diffusion layers in a Hele-Shaw geometry. , 2010, Physical review letters.

[4]  Hamdi A. Tchelepi,et al.  Convective dissolution of carbon dioxide in saline aquifers , 2010 .

[5]  A. Wit,et al.  Influence of buoyancy-driven convection on the dynamics of A+ B → C reaction fronts in horizontal solution layers , 2010 .

[6]  A. Wit,et al.  Active role of a color indicator in buoyancy-driven instabilities of chemical fronts , 2010 .

[7]  A. De Wit,et al.  Chemically driven hydrodynamic instabilities. , 2010, Physical review letters.

[8]  Karsten Pruess,et al.  Laboratory Flow Experiments for Visualizing Carbon Dioxide-Induced, Density-Driven Brine Convection , 2009, Transport in Porous Media.

[9]  T. Nishimura,et al.  Heat Transfer under Buoyancy-Induced Flow at the Chemical Reaction Front Using Thermochromic Liquid Crystal Sheet , 2009 .

[10]  A. De Wit,et al.  Dynamics of A + B --> C reaction fronts in the presence of buoyancy-driven convection. , 2008, Physical review letters.

[11]  A. Ureña,et al.  Pattern formation driven by an acid-base neutralization reaction in aqueous media in a gravitational field. , 2008, Physical review. E, Statistical, nonlinear, and soft matter physics.

[12]  K. Eckert,et al.  Acceleration of reaction fronts by hydrodynamic instabilities in immiscible systems , 2006 .

[13]  K. Eckert,et al.  PLUME AND FINGER REGIMES DRIVEN BY AN EXOTHERMIC INTERFACIAL REACTION , 1999 .

[14]  Rácz,et al.  Properties of the reaction front in an A+B-->C type reaction-diffusion process. , 1988, Physical review. A, General physics.

[15]  R. W. Griffiths.  Layered double-diffusive convection in porous media , 1981, Journal of Fluid Mechanics.