Why do Particle Clouds Generate Electric Charges?

TL;DR

This paper presents a simple, predictive model explaining how inert dielectric grains in collisional flows generate electrical charges, supported by simulations and experiments, addressing a long-standing scientific question.

Contribution

It introduces a novel, basic explanation for granular charging in collisional flows, validated through simulations and tabletop experiments.

Findings

Charge transfer occurs in collisions of identical dielectric grains in an electric field.

The model accurately predicts charging behavior observed in experiments.

Simulations confirm the theoretical predictions.

Abstract

Grains in desert sandstorms spontaneously generate strong electrical charges; likewise volcanic dust plumes produce spectacular lightning displays. Charged particle clouds also cause devastating explosions in food, drug and coal processing industries. Despite the wide-ranging importance of granular charging in both nature and industry, even the simplest aspects of its causes remain elusive, because it is difficult to understand how inert grains in contact with little more than other inert grains can generate the large charges observed. Here, we present a simple yet predictive explanation for the charging of granular materials in collisional flows. We argue from very basic considerations that charge transfer can be expected in collisions of identical dielectric grains in the presence of an electric field, and we confirm the model's predictions using discrete-element simulations and a tabletop granular experiment.