A method for measuring the charging tendency of powder in pneumatic conveyance through metal pipes

Abstract

The charging tendencies of powders of some synthetic high polymers are measured with a newly developed charging apparatus. The sample is continuously transported through a bent metal pipe using an air flow and is electrified by multiple frictions and collisions against the inner wall of the metal pipe. The transport speed V and the solid load d of the sample are changed from 1.4 to 2.8 m/s and 1.9 to 5.2 kg/m 3, respectively. The charge build-up of each examined is given by the empirical equation: Q = Q s [1 − k exp (−t/τ)]. The saturation charge Q s and the initial rate of charge accumulation q o [ = (d Q/d t) t=0 ] are found to depend on the transport speed and the material of the pipe. The initial rate of charge accumulation q o also depends on the solid load and in the case of a spherical PE sample, it can be described by an experimental equation obtained with aluminium pipe: q o = −2.47 V 0.4 d −1.07 × 10 −6 C/kg s. The saturation charge Q s of each sample used in this measurement at the same transport speed corresponds to the position of each sample in the familiar previously published triboelectric series [1–3].