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.

We numerically study the impact of a large sphere dropping into a prefluidized granular bed using a state-of-the-art hybrid discrete particle and immersed boundary (DP-IB) method. For the first time, both the gas-induced drag force and the contact force exerted on the intruder are investigated separately. Our results show that even for relatively large granular particles of 0.5. mm diameter, namely Geldart B particles, and an intruder of 1. cm, the drag exerted by the interstitial gas accounts for up to 5% of the total force experienced by the intruder. Our simulation results match well with existing experimental observations. This work shows that the current simulation scheme could become a tool to investigate the effect of interstitial gas on the dynamics of projectile impact cratering. More generally, the method allows for accurate simulation of the hydrodynamic effects of large internal objects moving through (pre-)fluidized granular beds.