Eur. Phys. J. E 7, 251-259 (2002)
DOI: 10.1140/epje/i200101142
Echo tracer dispersion in flows of polymer solutions through porous media: A tool for detecting weak permeability heterogeneities?
A. D'Onofrio1, 2, V.M. Freytes1, M. Rosen1, C. Allain2 and J.P. Hulin21 Grupo de Medios Porosos, F.I.U.B.A., Paseo Colon 850, 1063 Buenos Aires, Argentina
2 Laboratoire Fluides, Automatique et Systèmes Thermiques (UMR CNRS 7608) Bât. 502, Campus Universitaire, 91405 Orsay Cedex, France
hulin@fast.u-psud.fr
(Received 19 September 2001)
Abstract
Tracer dispersion in Newtonian and shear-thinning fluids (scleroglucan-water
polymer solutions) flowing through single and double porosity grain packings
has been studied experimentally using both classical transmission dispersion
and echo dispersion (in the latter, the concentration variation front is
pumped back through a detector at the inlet after penetrating for a chosen
distance into the sample). Transmission dispersion increases markedly in
both types of samples with the shear thinning index of the fluid at all
Péclet numbers (except when molecular diffusion is dominant). Echo and
transmission experiments give nearly identical dispersivity values for
Newtonian fluids while echo dispersivity is lower than transmission for
shear thinning ones. The normalized dispersivity difference has same order
of magnitude for single and double porosity samples and increases with the
shear thinning exponent
(by a factor of 2 between
and
). This difference may be due to heterogeneities
inducing permeability variations of small amplitude over distances of the
order of the sample section : their influence on tracer dispersion is partly
reversible with respect to a change of the flow direction and is only
detectable if it is amplified by the shear-thinning properties of the fluid.
47.55.Mh - Flows through porous media.
47.50.+d - Non-Newtonian fluid flows.
81.05.Rm - Porous materials; granular materials.
© EDP Sciences, Società Italiana di Fisica, Springer-Verlag 2002
