Fluid-particle suspension by gas release from a granular bed

TL;DR

This study experimentally investigates how gas injection through a granular bed in a Hele-Shaw cell creates a particle suspension, revealing a steady state driven by bubble-induced entrainment and sedimentation.

Contribution

It introduces a new experimental analysis of particle suspension dynamics caused by gas bubbles in a granular bed, including a phenomenological model of particle recirculation.

Findings

Existence of a stationary suspension state.

Average solid fraction can be estimated from the granular bed area.

Most particles are entrained through a global recirculation process.

Abstract

We have studied experimentally particle suspension when injecting a gas at the bottom of an immersed granular layer confined in a Hele-Shaw cell. This work focuses on the dynamics of particles slightly denser than the surrounding fluid. The gas, injected at constant flow-rate, rises through the granular bed then forms bubbles which entrain particles in the above liquid layer. The particles settle down on the edges of the cell, avalanche on the crater formed at the granular bed free surface, and are further entrained by the continuous bubbling at the center. We report the existence of a stationary state, resulting from the competition between particle entrainment and sedimentation. The average solid fraction in the suspension is derived from a simple measurement of the granular bed apparent area. A phenomenological model based on the balance between particle lift by bubbles at the center of the cell and their settling on its sides demonstrates that most of the particles entrained by bubbles come from a global recirculation of the suspension.