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Chemo-hydrodynamic pattern formation at interfaces

Research project PX/7/LP/25 (Research action PX)

Persons :

  • Prof.  DE WIT Anne - Université Libre de Bruxelles (ULB)
    Coordinator of the project
    Financed belgian partner
    Duration: 1/5/2003-1/3/2006

Description :

Hydrodynamically unstable chemical fronts or interfaces influenced by chemical reactions underly many industrial applications. The coupling of chemical reactions and hydrodynamics can occur in several ways. The two most common cases are nonlinear volume reactions that create their own self-organized interface (referred to as chemical fronts) and chemical reactions at liquid-liquid interfaces. Our objective is to characterize pattern formation due to the coupling between such chemical reactions at interfaces and hydrodynamic instabilities. Our focus is on clarifying the underlying physical mechanisms and corresponding stability properties of the interfaces through theoretical studies complemented by ground based and microgravity experiments. These studies aim to analyze the influence of the chemically-driven fluid flows on the changes in heat / mass transfer, on mixing rates and on spatio-temporal dynamics of concentrations.

Two prototype experiments are therefore analyzed, each of them representative of a broad class of systems. The first system focuses on hydrodynamic deformation and acceleration of autocatalytic chemical fronts. Due to concentration and temperature differences across a self-organized front, Rayleigh-Taylor or double-diffusive instabilities can develop when the front travels in a Hele-Shaw cell oriented vertically in the gravity field. In thin layers of solution in contact with air, surface tension effects can in addition come into play. Our research aims at a theoretical understanding of the spatio-temporal dynamics resulting from the coupling between these various hydrodynamic instabilities with the autocatalytic reactions. Experiments are performed by our collaborators in Szeged (Hungary) and in Magdeburg (Germany).

In the other prototype situation, which is a chemical reaction at a liquid-liquid interface, interfacial-tension effects are a key element leading to chemically driven interfacial convection or CDIC. Our focus is on understanding the physical mechanisms underlying the complex patterns observed which result from a combination of Rayleigh-Bénard, Rayleigh-Taylor, double-diffusive and Marangoni instabilities. We analyze by analytical and numerical work how a simple exothermic A+B->S chemical reaction can trigger and influence these various hydrodynamic instabilities in a two-layer system contained in a Hele-Shaw cell. Related experiments are performed in Dresden (Germany), in Toulouse (France) and are also tested in microgravity conditions to discriminate between the buoyancy- and Marangoni-driven effects.

Our collaborations takes place in the framework of the international research programme “Chemo-hydrodynamic instabilities at interfaces” sponsored by ESA and national space agencies.

Satellite(s) or flight opportunity(ies):

- Sounding Rockets

Field of research:

Physical Science: Fluid Physics

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