Integrated DEM–CFD modeling of the contact charging of pneumatically conveyed powders

• We present a model for contact charging of pneumatically conveyed powders.
• A discrete element model for the particles is coupled with CFD for the gas.
• The importance of including electrostatic interactions with walls is investigated.
• The charging behavior depends sensitively on details of the particle–wall contact.

A model is proposed that incorporates contact charging (also known as triboelectric charging) of pneumatically conveyed powders in a DEM–CFD framework, which accounts for the electrostatic interactions, both between particles and between the particles and conducting walls. The simulation results reveal that the influence of the electrostatic interaction between particle and wall is significant and should not be neglected, since it is found to influence both the spatial distribution of the powder in the duct, and the acquired charge of the particles. We find that there is a critical mean charge: only when the mean charge of the particles exceeds this value, the influence of the electrostatic particle–wall interaction starts to show. This critical charge is independent of the particle concentration in the duct. In this work we use a simple charging model based on the normal impact velocity. A lumped parameter α, dubbed charging efficiency, is introduced to account for the increased contact surface caused by particle rolling on impact due to a tangential component of the impact velocity. The applied model should therefore be viewed as a learning model. In a range of reasonable estimates of α, the charging behavior is non-linear and very sensitive to the value of α; this illustrates the complexity of the system. It also stresses the need for modeling tools to increase our understanding of the particle dynamics and charging behavior.

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