工业中粉体颗粒的荷电机理及数值模拟方法∗

摘要

Particles in industrial flows can be charged under an action of external electric field, while in the absence of external electric field, tribo-electrostatic charges are almost unavoidable in gas-solid two-phase flows due to the consecutive particle contacts. The particle charging may be beneficial, or detrimental. In the past decade considerable progress has been made in understanding the physics of particles charging. However, the particle charging mechanism, especially in the gas-solid phase flow, is still poorly understood. The purpose of this review is to present a clear understanding of the particle charging and movement of charged particle in two-phase flow, by summarizing the charging mechanisms, physical models of particle charging, and methods of charging/charged particle entrained fluid flow simulations. In this review, charged particles in industry, which would be beneficial (triboelectrostatic separation, electrostatic precipitator) or detrimental (electrification in gas-solid fluidized bed and manufacturing plant) are discussed separately. The particle charging through collisions could be attributed to electron transfer, ion transfer, material transfer, and/or aqueous ion shift on particle surfaces. For conductive particle contacts, the difference in work function is often used to explain the charge transfer. For insulation particle contacts, the charging tendency can be explained by the ion transfer and material transfer. In addition, aqueous ion shift transfer would be an important charge transfer mechanism considering water content in environmental conditions and the influences of temperature and humidity. The charges on particle through collision can be quantitatively predicted by using the particle charging model. According to the differently induced ways of charge transfer, the charging models are related to the external electric field, asymmetry contact, and/or aqueous ion shift on particle surfaces. In fact, the motions of particles in industry are influenced by fluid flow. The effect of fluid on particle dynamics makes the particle charging more complicated. Thus it is more reasonable to study the particle charging from the viewpoint of the gas-solid two-phase flow. The method combining particle charging model with computational fluid dynamics and discrete element method is applicable to the studying of the particle charging/charged processes in gas-solid two phase flow in which the charge behaviors are significantly influenced by the fluid mechanics behavior. By this method, the influence factors of particle charging, such as gas-particle interaction, contact force, contact area, and various velocities, are described systematically. This review presents a clear understanding of the particle charging and provides theoretical references on controlling and utilizing the charging/charged particles in industrial technology.%工业过程中粉体颗粒不可避免地会相互摩擦碰撞而荷电。荷电颗粒的存在可能会危害正常的工业生产过程，也可能对工业过程起促进作用。因此，荷电粉体颗粒及其特性受到了广泛的关注，但目前对粉体颗粒的荷电机理依然缺乏透彻的了解，尤其是在气固两相流动中的粉体颗粒荷电现象。事实上，工业中存在的粉体颗粒的运动都受到流体的影响，是典型的气固两相流系统，流体对粉体颗粒的作用使粉体颗粒接触的荷电现象变得更为复杂，因此从两相流动的观点来研究粉体颗粒荷电的物理本质就显得越来越重要。本文介绍了工业过程中的几种不同类型的粉体颗粒荷电行为，回顾了颗粒的荷电机理与描述颗粒荷电的数学模型。对于工业过程中颗粒的荷电现象及颗粒在多相流体中的动力学行为，介绍了研究颗粒受流体影响时荷电特性的数值模拟方法。本文旨在对粉体颗粒的荷电机理、应用以及研究方法进行梳理与探讨，为正确认识工业过程中粉体颗粒的荷电现象并加以控制利用提供理论借鉴。