CFD study of particle back-flow in pneumatic conveying systems due to triboelectrification

TL;DR

This study uses CFD simulations to investigate how electrostatic forces influence particle back-flow in pneumatic conveying systems, revealing that charged particles can reverse flow direction under certain conditions.

Contribution

It demonstrates that electrostatic forces can induce particle back-flow in pneumatic conveying systems, especially during discontinuous feeding, which was not previously well understood.

Findings

Electrostatic forces drive particles into low-velocity regions.

Particles with charge ≥ 5.04 fC can reverse flow direction.

Back-flow occurs during discontinuous particle injection.

Abstract

In industrial plants, pneumatic conveying systems are often used to convey particles from one location to another. Surprisingly, in bench-scale experiments, clusters of particles sometimes flow backward or upstream in the conveying channel. In this paper, the effect of electrostatic charge and forces on particle back-flow was investigated. Different conveying conditions with varying particle charges were simulated using computational fluid dynamics (CFD), and the resulting flow patterns were compared with CFD simulations of uncharged particles. In a channel flow with periodic boundary conditions in the streamwise and spanwise directions, it was found that electrostatic forces drive particles into low-velocity regions but do not reverse their flow. When transporting particles through a finite-length duct, electrostatic forces cause particles to settle close to the duct's inlet. Finally, when particles were injected into the duct in a pulse, back-flow was observed once particles obtained a charge of 5.04 femto-coulombs or more. The electrostatic forces decelerated the particles at the tail of the pulse and ultimately reversed their direction, whereas the particles at the head of the pulse were accelerated. Thus, it was concluded that electrostatic forces can cause particle back-flow in pneumatic conveying systems if particles are fed discontinuously.