Multi-scale modeling of gas-solid flows with charged particles

It has been known for centuries that materials tend to charge electrically when they come into mechanical contact. This charging, known as triboelectric charging, or tribocharging for short, is observed naturally in the large electric fields observed in volcanic eruptions and sandstorms as well as in many gas-solid industrial processes, from conveying pipes to polymerization reactors and triboelectric separators. The effects on gas-solid flow systems are particularly important because these systems often undergo large amounts of tribocharging due to frequent collisions between particles and walls. For these processes, the hydrodynamics of the gas-solid flows strongly influence the overall efficiency and safety of the system, and the hydrodynamics can be altered significantly by tribocharging and resulting electrodynamic forces. In this talk, how to describe the connection between the macroscopic behavior of gas-solid flow systems and tribocharging at particle-scale through a multi-scale modelling approach will be discussed. We have first developed Eulerian-Lagrangian (e.g., Computational Fluid Mechanics-Discrete Element Model) modelling approach accounting for tribocharging[1] and validated the model predictions through experimental data of granular vibrated and fluidized beds with charged particles[2,3]. As the Eulerian-Lagrangian modelling is limited to relatively small gas-solid systems, we have developed a kinetic-theory based transport equation for mean charge for bi- and mono-disperse particles coupled with a Eulerian-Eulerian (two-fluid) model for industrial-scale applications[5,6] using the validated charge model. We foresee that the developed modelling framework will inform industries which utilize gas-solid flows on how they can avoid hazards and inefficiencies associated with tribocharging, or even utilize this charging to their advantage.