Vertically shaken column of spheres. Onset of fluidization

TL;DR

This study experimentally investigates the onset of surface fluidization in a vertically vibrated column of spheres, challenging existing theoretical criteria and demonstrating that a critical acceleration is not sufficient to determine fluidization.

Contribution

The paper provides experimental evidence that the critical acceleration criterion is inadequate for predicting fluidization in a column of spheres, contrasting with previous theoretical and experimental findings.

Findings

Critical acceleration is not a proper criterion for fluidization.

Experimental results disagree with the simple acceleration threshold theory.

Comparison shows the need for more complex criteria for fluidization onset.

Abstract

The onset of surface fluidization of granular material in a vertically vibrated container, z=A cos(\omega t), is studied experimentally. Recently, for a column of spheres it has been theoretically found that the particles lose contact if a certain condition for the acceleration amplitude \ddot{z} \equiv A\omega^2/g = f(\omega) holds. This result is in disagreement with other findings where the criterion \ddot{z}=\ddot{z}_{crit}=const. was found to be the criterion of fluidization. We show that for a column of spheres a critical acceleration is not a proper criterion for fluidization and compare the results with theory.