Eur. Phys. J. E 3, 227-236
Diffusion of a single particle in a 3D random packing of spheres
I. Ippolito1 - L. Samson1 - S. Bourlès1 - J.-P. Hulin2
1 Groupe Matière Condensée et Matériaux
(UMR CNRS 6626), Université de Rennes 1, Bâtiment 11A,
Campus de Beaulieu, 35042 Rennes Cedex, France
2 Laboratoire
Fluides Automatiques et Systèmes Thérmiques (UMR CNRS 7608),
Université de Paris Sud, 91405 Orsay Cedex, France
irene.ippolito@univ-rennesl.fr
Received 5 November 1999 and Received in final form 30 March 2000
Abstract
We report an experimental study of the dispersion properties of
individual spherical particles of size d, moving under gravity in
a dry random packing of large spheres of size D. The diameter
ratio d/D is below the critical value 0.1547 above which beads
get pinned inside the packing . They move in this regime at a
constant mean velocity decreasing with the ratio d/D. We
analyse dispersion parallel and transverse to the mean velocity by
studying the bead distribution in the x-y plane at the exit of
the packing (radial dispersion) and the transit time distribution
(longitudinal dispersion) while varying the height H of the
bed. Diffusion in both directions is found to be governed
essentially by the diameter D of packed spheres and not by the
size d of the small beads. A dispersivity length characterising
the spreading amplitude is determined. Comparisons between
transverse and longitudinal dispersion demonstrate that both
processes have similar properties. A key parameter is the diameter
D which controls the path length of the particles.
PACS
81.05.Rm Porous materials; granular materials
- 45.70.Mg Granular flow: mixing; segregation and stratification
- 05.40.Fb Random walks and Levy flights
Copyright EDP Sciences, Società Italiana di Fisica, Springer-Verlag
