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.