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Modelling of Gas-Solid Flows with Tribocharging Ozel, Ali


Triboelectrification or tribocharging is a process by which two materials exchange electric charge upon mechanical contact and it has been observed in many industrial applications such as fluidised beds, pneumatic conveying systems and silo flows. In this study, we seek to shed light on dynamics of tribo-electrically charged particles in gas-solid flows through a combination of computational modelling and experiments. To study how tribocharging affects hydrodynamics of gas-solid flows, we have developed Computational Fluid Dynamics-Discrete Element Method (CFD-DEM) augmented by a finite-volume based Poisson solver for electric field and a charge transfer model. In the charge model, the charging tendency of particles is captured by effective work function difference between the contacting surfaces and the electrical field at contact. In recent studies, we performed vibrated and fluidized bed experiments and measured average charge on polyethylene particles at different humidity conditions. We also performed CFD-DEM simulations of the same flow configurations and showed that the predicted charge values were in a good agreement with experimental data. As CFD-DEM simulations are limited to flow systems with a relatively small number of particles and there is a need to examine the interplay of flow and tribocharging in large-scale systems, we have also formulated a kinetic-theory based Euler-Euler model for monodisperse particles with tribocharging. To this end, we derived the mean charge transport equation from the Boltzmann equation allowing for conduction of mean charge through collisions in the presence of electric field, and boundary condition capturing tribocharging at the wall. These models were implemented in an open-source continuum physics software, OpenFOAM. Model predictions were then assessed through comparisons with hard-sphere Euler-Lagrange simulations and experimental studies.

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