Granular compaction by fluidization

Alexis Tariot,Philippe Gondret,Georges Gauthier,F Radjai,S Luding,S Nezamabadi,J.Y Delenne

doi:10.1051/epjconf/201714010003

Abstract

How to arrange a packing of spheres is a scientific question that aroused many fundamental works since a long time from Kepler’s conjecture to Edward’s theory (S. F. Edwards and R.B.S Oakeshott. Theory of powders . Physica A, 157 : 1080-1090, 1989), where the role traditionally played by the energy in statistical problems is replaced by the volume for athermal grains. We present experimental results on the compaction of a granular pile immersed in a viscous fluid when submited to a continuous or bursting upward flow. An initial fluidized bed leads to a well reproduced initial loose packing by the settling of grains when the high enough continuous upward flow is turned off. When the upward flow is then turned on again, we record the dynamical evolution of the bed packing. For a low enough continuous upward flow, below the critical velocity of fluidization, a slow compaction dynamics is observed. Strikingly, a slow compaction can be also observed in the case of “fluidization taps” with bursts of fluid velocity higher than the critical fluidization velocity. The different compaction dynamics is discussed when varying the different control parameters of these “fluidization taps”.

Highlights

Since Edwards’ theory on piles of athermal spheres [1], several ways to compact a dry granular pile have been tried and studied using vibrations [2], taps [3,4,5], shear [4, 6] or heating cycles [7, 8]
Shearing appears the more efficient way to compact [6] with a global solid volume fraction φ 0.66 reached after about 104 cycles which is significantly higher than the random close packing φRCP 0.64
It is well known that applying an upward viscous flow to a granular pile will generate a global decompaction of the granular bed that leads to a fluidized bed

Summary

Introduction

Since Edwards’ theory on piles of athermal spheres [1], several ways to compact a dry granular pile have been tried and studied using vibrations [2], taps [3,4,5], shear [4, 6] or heating cycles [7, 8]. Shearing appears the more efficient way to compact [6] with a global solid volume fraction φ 0.66 reached after about 104 cycles which is significantly higher than the random close packing φRCP 0.64. Schröter et al.[9] showed for instance that cycles of fluidization/sedimentation of a collection of non-Brownian spheres lead to a higher solid fraction of the granular bed at rest for lower fluidization velocities, extending the works of Onada and Liniger[10]

Methods

Results

Conclusion