Secondary flows drive triboelectric powder charging in pneumatic conveying

TL;DR

This study uses high-resolution simulations to show that secondary flows in ducts significantly influence triboelectric powder charging, leading to faster charging, more uniform charge distribution, and altered particle and fluid dynamics compared to channel flow.

Contribution

The paper reveals how secondary flows in duct geometries enhance powder charging and distribution, providing new insights into controlling triboelectric effects in pneumatic conveying systems.

Findings

Particles charge faster in duct flow than in channel flow.

Secondary flows promote better mixing and uniform charge distribution.

Electrostatic forces influence particle distribution and flow behavior.

Abstract

Highly resolved simulations reveal the fundamental influence of a carrier fluid's flow dynamics on triboelectric powder charging. We found that particles transported through a square-shaped duct charge faster than in a channel flow caused by secondary flows that led to more severe particle-wall collisions. Specifically, particles with a Stokes number of 4.69 achieve 85 % of their equilibrium charge approximately 1.5 times faster in duct flow than in channel flow. Also, charge distribution is more uniform in a duct cross-section compared with a channel cross-section. In channel flow, particles are trapped near the walls and collide frequently due to limited movement in the wall-normal direction, causing localized charge buildup. In contrast, duct flow promotes better mixing through secondary flows, reducing repeating collisions and providing uniform charge distribution across the cross-section. Upon charging, electrostatic forces significantly reshape particle behaviour and distribution. Once the powder achieves half of its equilibrium charge, particles increasingly accumulate at the wall, leading to a reduced concentration in the central region. These changes in particle distribution have a noticeable impact on the surrounding fluid phase and alter the overall flow dynamics. These findings open the possibility for a new measure to control powder charging by imposing a specific pattern.