Triboelectric charging of polydisperse particles in a developed pipe flow

A framework has been developed for computing the tribocharging of particles while they are being conveyed pneumatically through high-velocity circular pipes. Fully-developed flow and particle conditions are considered. With four compositions of particle ranging from nanometre sizes to 100 μm, the radial electrostatic field induced by the space charge of all the particles was approximated, and then updated with the different radial distributions. Simple models for the response of the particles to turbulence, for the radial drift induced by the electrostatic field, for inter-particle collisions, and for the asymptotic charging at the wall were developed. For particle numbers totalling 3x10⁹/m³, it was shown that collisions can be ignored. Large differences in the radial number density distributions for different particle sizes were found, from uniformity for those under about 5 μm, to heavy concentration at the wall for the larger ones.