Numerical analysis of contact electrification of non-spherical particles in a rotating drum

Contact electrification is generally referred to as the charge transfer process between particles during collisions. The transferred charge can be accumulated on the surface of the particles especially for insulating materials with irregular shapes, which can lead to a non-uniform charge distribution and eventually affects the charge accumulation process. In this study, in order to investigate the influence of the particle shape on contact electrification, a sphere-tree multi-sphere method and a contact electrification model are implemented into the discrete element method (DEM) to model the charging process of irregular particles in a rotating drum. Irregular particles with various Sauter mean diameters but the same maximum diameter and equivalent volume diameters are considered. The charge distribution and accumulation on the particles are investigated. It is found that the charge transfer originates from the contact between the particle and the drum due to the contact potential difference and initially takes place primarily at the region near the wall of the drum. The charge eventually propagates to the entire granular bed. The charge of the particles increases exponentially to an equilibrium value. For particles with the same maximum diameter, a larger charging coefficient is obtained for the particles with smaller Sauter mean diameters and sphericities, which leads to a faster charge accumulation, while for particles with the same equivalent volume diameter and fill ratio, similar charging coefficients are observed. A non-uniform intra-particle charge distribution is induced on each individual multi-sphere particle.

接触起电通常是指粒子碰撞过程中的电荷转移过程。转移的电荷可在粒子表面累积，特别是对于形状不规则的绝缘材料，这会导致电荷分布不均匀，并最终影响电荷累积过程。在本研究中，为了探究粒子形状对接触起电的影响，将一种球 - 树多球方法和一个接触起电模型应用到离散元方法（DEM）中，以模拟转鼓中不规则粒子的充电过程。考虑了具有不同索特平均直径但相同最大直径和等效体积直径的不规则粒子。对粒子上的电荷分布和累积情况进行了研究。研究发现，由于接触电势差，电荷转移源于粒子与转鼓之间的接触，并且最初主要发生在转鼓壁附近区域。电荷最终会传播到整个颗粒床。粒子的电荷呈指数增长直至达到平衡值。对于具有相同最大直径的粒子，索特平均直径和球形度较小的粒子具有较大的充电系数，这导致更快的电荷累积，而对于具有相同等效体积直径和填充率的粒子，观察到相似的充电系数。在每个单独的多球粒子上会产生不均匀的粒子内电荷分布。