Surface coating induced lubrication in flowing granular materials

TL;DR

This study uses simulations to explore how surface coating with lubricants affects the flow of granular materials on an incline, revealing a non-monotonic relationship between lubricant content and flow rate.

Contribution

It introduces a computational approach to understand powder lubrication, showing how coating influences flow behavior and flow rate dependence on lubricant content.

Findings

Flow rate increases then decreases with lubricant content.

Lubricant coating reduces inter-particle friction.

High lubricant content leads to densification and damping.

Abstract

We investigate the flow of spherical, bulk granular particles down an inclined plane mixed with small-sized spherical lubricant particles using discrete element method simulations. Predefined cohesive interaction is implemented between lubricant and bulk particles, enabling the coating of the former over the latter. The overall flow rate exhibits non-monotonic dependence on lubricant content. Initially, it increases with lubricant addition, reaches a maximum at an intermediate lubricant content, and decreases for even higher lubricant content. The increase in the flow rate is attributed to a lower inter-particle friction coefficient between lubricant-coated bulk particles. The decrease in the flow rate at higher lubricant content, on the other hand, is attributed to enhanced densification and increased damping between crowded particles. Both these occurrences are examined using various flow level characteristics. The simulation results are found to be in qualitative agreement with previous experimental results. Overall, the outcome integrates novel computational insights and prior experimental results to enhance the understanding of the powder lubrication phenomena.