J. Phys. II France
Volume 6, Numéro 11, November 1996
Page(s) 1639 - 1654
DOI: 10.1051/jp2:1996153
J. Phys. II France 6 (1996) 1639-1654

Tracer Dispersion in a Polymer Solution Flowing Through a Double Porosity Porous Medium

A. Paterson1, A. d'Onofrio1, 2, C. Allain1, J.P. Hulin1, M. Rosen2 and C. Gauthier3

1  Laboratoire de Fluides, Automatique et Systèmes Thermiques URA CNRS 871, Bâtiment 502, Université Paris-Sud, 91405 Orsay Cedex, France
2  Grupo de Medios Porosos, Facultad de Ingenieria, Paseo Colon 850, 1063 Buenos Aires, Argentina
3  Laboratoire des Matériaux et Structures du Génie Civil UMR CNRS-LCPC 113, Parc Club de la Haute Maison, 77420 Champs-sur-Marne, France

(Received 30 April 1996, received in final form 29 July 1996, accepted 31 July 1996)

Experimental results on the dispersion of a tracer in a polymer solution flowing through a nonconsolidated packing of porous grains are reported. We use a scleroglucane solution with a shear viscosity decreasing as a power law of the shear-rate over a broad range: the characteristic exponent $\alpha$ is varied between 0.40 and 0.77 by changing the polymer content. Porous grains of size $d_{\rm g} = 500~\mu $m and internal porosity $30\%$ are obtained by grinding sintered glass beads of initial diameter $110~\mu$m. Dispersion measurements use a saline tracer at Péclet numbers Pe between 0.7 and 700. At a constant Pe, the dispersivity $l_{\rm D} = K/U$ (K being the longitudinal dispersion coefficient) increases with $\alpha$ (by a factor of 6 between $\alpha = 0$ and $\alpha =
0.77$ around Pe = 10). At some Pe values, early arrival time effects are observed. The dispersivity also increases with Pe at all $\alpha$ values in the range of transition from diffusive towards convective transport in grains. These results are assumed to be due to the non-Newtonian characteristics of the solution increasing the contrast both between low and high velocity flow paths and between the inside and the outside of the grains.

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