Abstract:

In past decades, the electrostatics of granules and granular flows has obtained more and more attention due to many industrial problems and development of new technologies. The collisions between granule-granule and granule-wall generate electrostatics. The occurrence of electrostatic can be affected by a variety of factors. As the contact between the granular and the wall, the accumulation of electrostatic charge on their surfaces can reach to an equilibrium state. The present work reviewed electrostatic generation and electrostatic equilibrium in pneumatic conveying granules systems. Two main contact charging ways between granule and wall (collision electrification and friction electrification), granular flow pattern and dynamic analysis were analyzed emphatically. The factors affecting the charging process of granules were discussed, including external conditions (temperature, relative humidity), granules geometry conditions (size, shape, contact area, roughness) and stress conditions. Besides, the numerical calculations of electrostatics in pneumatic conveying granules systems were introduced briefly. Finally, in order to clarify the mechanism of electrostatics in the pneumatic conveying granules systems, the physical mechanism of electrostatics in single granules was analyzed. This review revealed that the working mechanism of electron transfer due to collision or friction remains was not fully understood. These issues is expected to be resolved gradually in the future.

Key words: electrostatic interactions, granules, pneumatic conveying, contact electrification

摘要：

在过去的几十年里，由于许多工业问题和相关新技术的发展，颗粒和颗粒流的静电学得到了越来越多的关注。颗粒-颗粒和颗粒-壁面之间发生碰撞从而产生静电。静电的发生会受多种因素的影响，随着颗粒与壁面之间的接触会在它们的表面产生静电荷的积累，静电量可以达到饱和状态。本文分别综述了气力输送颗粒系统中的静电发生及静电平衡，着重分析了颗粒与壁面之间接触带电的两种方式（碰撞带电和摩擦带电）、颗粒流模式及受力情况，讨论了颗粒带电过程所受的影响因素，包括外界条件（温度、相对湿度）、颗粒几何条件（尺寸、形状、接触面积、粗糙度）以及受力条件（摩擦力、常压）等。此外，对气力输送颗粒系统中静电的数值计算作了简单介绍。最后，为澄清气力输送颗粒系统中静电发生的机理，对单颗粒发生静电的物理机制进行了分析。根据对相关研究结果的总结，发现由于碰撞或摩擦造成的电荷转移的工作机制尚未完全明了，这些问题将在未来逐步得到解决。

关键词: 静电效应, 颗粒, 气力输送, 接触带电