Electrostatics of the granular flow in a pneumatic conveying system

The phenomenon of electrostatic charge generation and its effects on granular flow behavior in a pneumatic conveying system was studied. The main parameters used for quantitative characterization of the phenomenon were the induced current, particle charge density, and equivalent current of the charged granular flow. These were measured using a digital electrometer, Faraday cage, and modular parametric current transformer, respectively. Three different flow patterns corresponding to different electrostatic effects within the pneumatic conveying system were observed, and these were named the disperse flow, half-ring flow, and ring flow patterns. It was found that the induced current, particle charge density, and equivalent current increased with decreasing flow rates. Electrostatic effects generally become stronger with time, and this may lead to clustering behavior occurring even in the disperse flow regime. The effects of several factors such as pipe wall material, particle composition, relative humidity of the conveying air used, and the presence of an antistatic agent in the system were investigated and found to be important in determining the electrostatic charge generation characteristics and granular flow patterns observed.