Tribo-charging of binary mixtures composed of coarse and fine particles in gas–solid pipe flow

Abstract

Experiments were conducted to investigate the effect of adding fines on the tribo-charging of coarse glass beads. Four types of fines, i.e., copper, stainless steel, uncoated and silver-coated fine glass beads, mixed with 240–830μm glass beads were conveyed by air through a stainless-steel spiral pipe acting as a tribo-charger. Regardless of the type or electrical conductivity of the fine particles tested, adding small amounts of fines (up to 10wt%) to coarse glass beads resulted in a sharp increase in the mass and surface charge densities of the particles. In general, the profiles of the mass and surface charge densities of the fine–coarse particle mixtures as a function of the mixture composition were determined by the relative magnitude of contact potential differences and the total surface areas of all the components. The dominant particle tribo-electrification mechanism switched from coarse particle–wall contacts to fine particle–wall contacts when the fines weight percentage in the mixture exceeded 10%. A model was developed to predict the mass charge density of binary mixtures as a function of the mixture composition.