Influence of the initial charge on the triboelectrification of millimeter size set of particles in an inclined tube

Abstract

In this paper, the triboelectric charge buildup on a set of initially charged particles is investigated. During the study, 30 g of charged polypropylene particles of 2–3 mm size were repeatedly passed through a 1 m inclined copper or polyvinylchloride (PVC) tube. At the tube output, the charge is measured after each passage, allowing the cumulative charge evolution over time to be measured. The obtained curves are fitted to an exponential model to extract the time constant of the process. For each experience, particles are first charged at different levels and polarities relatively to the presumed saturation charge using both corona discharge and triboelectricity. The obtained results show that the initial charge value and polarity strongly affect the subsequent triboelectricity variations as well as the process speed. The triboelectric charge evolution is mainly related to the ratio between initial charge (Q0) and saturation charge value (Qs). Therefore, the particle's charge will increase if Q0 < Qs, decrease if Q0 > Qs, or be maintained at the same level when Q0 ≈ Qs. The particles can change polarity and be recharged with the opposite sign according to the tube and the initial charge level. This triboelectric charge behavior is explained based on the surface energy state in the electron transfer model. Furthermore, increasing the particles quantity from 5 g to 60 g reduces the saturation charge from 11 nC/g to 2.5 nC/g, which is approximately 77% less. Surface potential distribution measurements show an uneven distribution with less charge in large amounts compared to lower amounts.