Volume 67, Number 3, August 2004
|Page(s)||369 - 375|
|Section||Electromagnetism, optics, acoustics, heat transfer, classical mechanics, and fluid dynamics|
|Published online||01 July 2004|
Simple model for reverse buoyancy in a vibrated granular system
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
Corresponding author: email@example.com
Accepted: 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.
PACS: 45.70.-n – Granular systems / 45.70.Mg – Granular flow: mixing, segregation and stratification / 81.05.Rm – Porous materials; granular materials
© EDP Sciences, 2004
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