Triboelectric charging of monodisperse particles in fluidized beds

Abstract

To investigate the interplay between particle charging and hydrodynamics in fluidized beds, models for triboelectric charging and electrostatic forces were built into a computational fluid dynamics‐discrete element method model. Charge transfer was governed by the difference in effective work function between contacting materials as well as the electric field at the point of contact. Monodisperse particles were fluidized with an effective work function difference between the particles and the conducting walls. For smaller work function differences, hydrodynamics were not changed significantly as compared with an uncharged case. In these simulations, the average charge saturated at a value much lower than the value anticipated based on the work function difference, and a unimodal distribution of charges was observed. For larger work function differences, particles stuck to walls and bed height oscillations due to slugging were less pronounced. For these cases, a bimodal distribution of charges emerged due to effects from strong electric fields. © 2016 American Institute of Chemical Engineers AIChE J, 63: 1872–1891, 2017

Experimental and numerical study of wall layer development in a tribocharged fluidized bed

“…This increases the average contact area and hence the average charge transferred in each collision. Based on the soft-sphere contact model, Kolehmainen et al (2017a) concluded that if damping forces are neglected, the ratio of the charge that would be transferred in a real contact to the charge transferred in a simulated 'soft' contact is…”

“…A list of so-called interacting cells is constructed at the beginning of the simulations to track the location of the particles in the computational mesh. The short-range term is not limited by a prescribed cutoff radius as in Kolehmainen et al (2016Kolehmainen et al ( , 2017a but covers all the particles located in the interacting cells. The list of interacting cells is determined according to the desired minimum distance of the short-range term (δ s,min ).…”

“…Differing from Kolehmainen et al (2016Kolehmainen et al ( , 2017a, the correction term is equal for all particles in a cell, so the electric field correction can be conducted cell by cell before mapping the long-range field to the particles. In order to evaluate the charge transfer between particles, the electric field at the contact point of particles i and j is approximated as where E r,ij is the electric field due to other sources than the colliding particles.…”

“…For example, all the particles in cell A contribute to the short range field of the particles in cell B if the shortest distance between the cells is below δ s,min . Similarly to Kolehmainen et al (2016Kolehmainen et al ( , 2017a, the long-range field is evaluated as the gradient of the electric potential φ over the computational mesh:…”

Surface contact charging

“…It does not describe the microscopic chemistry or physics of how charges rearrange to produce the phenomenological behaviors defined by Eq's [1] and [2]. Several groups have published important contributions, for example dealing with changes to effective material work functions due to the fields produced by charged particles 11,12,13 , and with carriers that may be responsible for surface charge transport 14,15 . Second, the change in polarization on a particle inevitably feeds back on itself -i.e.…”