The Scaling of Triboelectric Charging Powder Drops for Industrial Applications

TL;DR

This study investigates how triboelectric charging scales with powder mass across different sizes, revealing that the simple linear relation breaks down at industrial scales and providing a new understanding of charge behavior.

Contribution

It introduces a detailed analysis of triboelectric charge scaling across small to large industrial powder quantities, challenging previous assumptions of linearity.

Findings

Charge scales with mass as Q ∝ m^b with 0.68 ≤ b ≤ 0.86

Scaling relation breaks down before reaching industrial scales

Scaling exponent varies with humidity but remains consistent across powders

Abstract

Triboelectrification of granular materials is a poorly understood phenomenon that alters particle behaviour, impacting industrial processes such as bulk powder handling and conveying. At small scales ($< 1 g$) net charging of powders has been shown to vary linearly with the total particle surface area and hence mass for a given size distribution. This work investigates the scaling relation of granular triboelectric charging, with small, medium ($< 200 g$), and large-scale ($\sim 400 kg$) laboratory testing of industrially relevant materials using a custom powder dropping apparatus and Faraday cup measurements. Our results demonstrate that this scaling is broken before industrially relevant scales are reached. Charge (Q) scaling with mass (m) was fitted with a function of the form $Q \propto m^b$ and $b$ exponents ranging from $0.68\ \pm\ 0.01$ to $0.86\ \pm\ 0.02$ were determined. These exponents lie between those that would be expected from the surface area of the bulk powder ($b = 2 / 3$) and the total particle surface area ($b = 1$). This scaling relation is found to hold across the powders tested and at varying humidities.