Mechanisms of particle entrainment in confined gas-particle systems under moving boundaries

TL;DR

This study uncovers that particle entrainment in confined gas-particle systems driven by moving boundaries is primarily governed by the mechanical work done on particles, rather than peak forces, providing a new framework for understanding boundary-induced transport.

Contribution

The paper introduces a work-based framework for particle entrainment, highlighting the combined role of pressure-gradient and unsteady drag forces under moving boundary conditions.

Findings

Entrainment is driven by the work performed on particles, not just pressure or peak forces.

Boundary kinematics influence entrainment by altering force work duration.

A unified energetic measure predicts the final entrained mass.

Abstract

Particle entrainment in confined gas-particle systems driven by moving boundaries is central to many industrial and natural processes, including pharmaceutical manufacturing, food processing, and chemical engineering. Although often termed a "suction effect," its physical origin remains unclear, especially under unsteady flow, strong particle interactions, and transient force networks. Here we study suction-induced entrainment in a prototypical confined system using high-fidelity coupled CFD-DEM simulations resolving unsteady gas flow and discrete particle motion with moving boundaries. By decomposing the forces on individual particles, we show that suction is not purely pressure-driven, but results from the combined action of pressure-gradient and unsteady drag forces generated by boundary-accelerated flow. Despite the heterogeneous and transient force fields, the final entrained mass is found to be governed primarily by a single energetic measure: the mechanical work performed on the particle assembly in the entrainment direction during boundary motion, rather than by peak instantaneous forces. Varying boundary kinematics demonstrates that changes in displacement or velocity history control entrainment mainly by modifying the duration over which fluid-particle forces perform work. These results reveal an organizing principle for suction-driven entrainment and establish a work-based framework for boundary-induced particle transport in confined gas-particle systems.