Density fingering of reaction-diffusion fronts in porous media
description
Transcript of Density fingering of reaction-diffusion fronts in porous media
Density fingering of reaction-diffusion fronts in porous media
L. Macias; D. Müller; N. Berrueta; L. Riolfo and A. D'Onofrio
A. ZaltsC. El HasiD. Rubio
Universidad Nacional General Sarmiento
A. De WitP. Trevelyan
Université Libre de Bruxelles
Grupo de Medios Porosos,Facultad de Ingeniería, Universidad de Buenos Aires,Argentina
In collaboration with:
Objectives
Experimental study of Rayleigh-Taylor instability on reaction-
diffusion fronts
two kinds of reactions
the acid autocatalysis of Chlorite-Tetrathionate (CT).
a simple exothermic neutralization reaction, NaOH solution and HCl solution (Acid-Base)
• Hele-Shaw cells and Porous Media
What is the difference between the two kinds of reaction?
• Chemical kinetic constant q
• The main difference is the stationary travelling wavefront
qCT = 2.4×104 M-3s-1qAB = 1.4×1011 M-1s-1CT
V
J. Yang, A. D´Onofrio, S. Kalliadasis, A. de Wit. J. Chem. Phys. 117, 9395 (2002)
reactants
product
conc
entra
tion
position
Acid - Base
P. Trevelyan, A. De Wit.
product
reactants
conc
entra
tion
position
Rayleigh – Taylor instability modified by chemical reaction in the interface
without chemical reaction with chemical reaction
Grupo de Medios Porosos, FIUBA (2002) Grupo de Medios Porosos, FIUBA (2004)
g
Rayleigh – Taylor instability modified by chemical reaction in the interface
without chemical reaction with chemical reaction
reactants
product
g
Mixing zone is smaller
x
Density profile
Rayleigh – Taylor instability modified by chemical reaction in the interface
D. Lima, A. D´Onofrio, A. De Wit, J. Chem. Phys. 124, 014509 (2006)
Effect of temperature (CT reaction)
Chlorite-Tetrathionate (CT)
Is an exothermic reaction
thermals effects are very important
Effect of temperature (CT reaction)
G. Garcia Casado, L. Tofaletti, D. Müller, A. D´Onofrio,. J. Chem. Phys. 126, 114502 (2007)
t = 140s
t = 80s
t = 140s
t = 210s
t = 140s
t = 210s
1 cm
t = 140s
t = 210s
1 cm
t = 140s
t = 210s
1
1 cm
Temperature
T = 12.4ºC T = 20.5ºC T = 39.4ºC
Effect of temperature (CT reaction)
G. Garcia Casado, L. Tofaletti, D. Müller, A. D´Onofrio,. J. Chem. Phys. 126, 114502 (2007)
Effect of temperature (CT reaction)
G. Garcia Casado, L. Tofaletti, D. Müller, A. D´Onofrio,. J. Chem. Phys. 126, 114502 (2007)
Front evolution at the inlet of the porous medium (CT reaction)
Porous medium
Helle shaw cell
3.5 cm
Grupo de Medios Porosos, FIUBA (2006)
Mix
ing
zone
t (s)
reactants
product
x
Density profile CT reaction
Acid - Base reaction
g
x
Density profile Acid - Base reaction
Acid
Base
Acid
Base
Acid - Base reaction
4.5 cmA <B
A. Zalts, A Ureña, D. Rubio, C. El Hasi, A. D´Onofrio. PRL (sent to publish)
Acid - Base reactionAcid - Base reaction
Equation of system Numerical results
P. Trevelyan, A. De Wit.
Acid
Base
g
Acid - Base reaction
t=490min t=2520min t=6650min t=490min t=2518min t=6648 min t=260 min t=2518min t=6648min
1 cm
0.1M 0.03M 0.01M
Acid - Base reaction
Variations of the mixing zone as a function of time for different concentrations.
Power spectra of the fingers for different concentrations. Note that the basic modes increases when the solution concentration increases.
Acid - Base reaction
Acid - Base reactionConclusion
• The Rayleigh – Taylor instability is modified by chemical reactions in the interface producing a decrease of the mixing zone (CT reaction).
• Temperature is a very important factor in this kind of systems as it could produce the disappearance of the instability (CT reaction).
• Even with an initial stable density profile, this chemical reaction (Acid – Base reaction) develops instabilities.
• In the Acid – Base case the mixing zone increases when the concentration decreases.