Tribocharging properties of wheat bran fragments in air-solid pipe flow

•Tribocharging properties of different bran tissues were investigated.•Tribocharging characters of bran tissues in three kinds of tubes were compared.•A mechanism of tribocharging in air-solid pipe flow was built.•Influences of flow rate and water content on tribocharging were studied.

Triboelectric separation (TS) has been used to separate aleurone particles from wheat bran fragments, but its mechanism remains poorly understood. In this study, the tribocharging properties of different bran tissues in the pipes made of Teflon, Nylon and stainless steel were investigated. The effects of air flow rate and water content on tribocharging were also studied. The results showed that, after tribocharging with Teflon pipe, the total charges of the bran fragments were positive, and decreased with the times of tribocharging, while, in Nylon pipe, the total charges obtained by the bran fragments were negative initially, then increased to be positive. The more aleurone cells in bran fragments, the more their total charges changed. After tribocharging with steel pipe, the total charges of bran fragments were positive and almost constant. The results of TS indicated that the polarities of the charges obtained by aleurone and pericarp particles were reversed by the pipe materials. Based on the results, a mechanism of tribocharging in air-solid pipe flow was built to explain the charging diversity of the wheat bran tissues in TS.