Characterization of Granular Electrostatics Generation

Jinzhui Li¹, Jun Yao¹, Yanlin Zhao^1*, Chi-Hwa Wang²

¹Beijing Key Laboratory of Process Fluid Filtration and Separation, College of Mechanical and Transportation Engineering, China University of Petroleum-Beijing, Beijing 102249, People’s Republic of China

²Department of Chemical and Biomolecular Engineering, National University of Singapore, 4 Engineering Drive 4, 117585, Singapore

* Corresponding author, Email address: ylzhao@cup.edu.cn (Y. Zhao)

ABSTRACT

Granule electrostatics is widely found in most granule engineering areas. However, the working mechanism has never been fully understood due to its sensitivity to working conditions, such as granule geometrical shape (including length-ratio and front-facing angle), contact area, granule material, relative humidity, sliding velocity, sliding orientation and normal stress. In this work, single granule was designed to slide along a metal plate and the electrostatics charges generated were measured via an electrometer connected with a computer. The working factors above have been considered for two kinds of granules made of PVC or coal. Regarding the geometrical factors, it is found that granules with larger length-ratio tend to produce more electrostatics, the slender or sharper granules tend to have higher capability of electrostatics generation and triangular granules generate more electrostatics than trapezoidal granules. In addition, electrostatics increase with decreasing granule front-facing angle and charges tend to gather at the granule tip. Regarding the granule material, it is found that coal granule tends to generate more electrostatics in comparison with PVC granule. The sequence of the relative work function for the three materials used in this work from high to low is given by the following sequence: PVC, stainless steel and coal. Regarding surrounding factors, it is found that electrostatics increases with granule contact area and such trend increases with decreasing relative humidity. Electrostatics generated increases with decreasing relative humidity and sliding velocity. Granule sliding orientation does affect electrostatics. In this work, granules sliding with smaller front-facing angle as well as shorter side tend to generate more electrostatics. Electrostatics increases with normal stress.

Keywords: Electrostatics; Charge Generation; Granule.