2022 Impact factor 1.8
Soft Matter and Biological Physics

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

Received 5 November 1999 and Received in final form 30 March 2000

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.

81.05.Rm Porous materials; granular materials - 45.70.Mg Granular flow: mixing; segregation and stratification - 05.40.Fb Random walks and Levy flights

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