Simple model for reverse buoyancy in a vibrated granular systemG. Gutiérrez1, O. Pozo1, L. I. Reyes1, R. Paredes V.2, J. F. Drake3 and E. Ott3
1 Departamento de Fisica, Universidad Simón Bolivar Apartado 89000, Caracas 1080-A, Venezuela
2 Centro de Fisica, Instituto Venezolano de Investigaciones Cientificas Apartado Postal 21827, Caracas 1020-A, Venezuela
3 University of Maryland - College Park, MD 20742-2431, USA
(Received 15 August 2003; accepted in final form 1 June 2004)
We report an experimental study of the motion of a large sphere immersed in a deep dry granular bed, subjected to vertical sinusoidal vibrations. Under certain conditions large heavy objects immersed in a homogeneous vibrated granular medium rise and similar light ones sink to the bottom. This is called reverse buoyancy. We have measured the vertical velocity of immersed large spheres, as a function of their density, under conditions for which reverse buoyancy is observed. We propose a one-dimensional mechanical model, based on the assumption that a cyclic fluidization of the medium occurs. With this model, that takes into account a buoyancy force and a frictional drag, we obtain, under the conditions of our measurements, the rising velocity for heavy objects and the sinking rate for light ones. The model yields a very good qualitative and quantitative agreement with our experiments.
45.70.-n - Granular systems.
45.70.Mg - Granular flow: mixing, segregation and stratification.
81.05.Rm - Porous materials; granular materials.
© EDP Sciences 2004