Geometric control of powder jet dynamics and energy dissipation

TL;DR

This study investigates how the geometry of a concave surface influences powder jet dynamics and energy dissipation, revealing a scaling relation and a mechanical model that explain the observed behavior.

Contribution

It systematically analyzes the effect of concave radius on powder jet ejection velocity and height, establishing a quantitative framework for powder flow dissipation.

Findings

Increasing concave radius broadens jets and reduces velocity and height.

Jet height scales linearly with concave radius, modulated by energy dissipation.

A mechanical model reproduces the observed scaling behavior.

Abstract

Applying an impulsive force to a powder layer shaped with a concave surface generates a sharp powder jet. This phenomenon has been proposed as a method for evaluating the flowability of powders from small amount of samples. In this study, we systematically varied the radius of the initial concave shape as a controllable parameter and quantitatively examined the resulting jet dynamics, focusing on ejection velocity and maximum height. Our high-speed observations revealed that increasing the concave radius led to broader jets with significantly reduced velocity and maximum height. These dynamic quantities followed a scaling relation with drop height, while the scaling coefficient decreased with the concave radius, indicating that the surface geometry directly governs the extent of energy dissipation. Furthermore, a minimal mechanical model incorporating the sliding distance and velocity squared type dissipation of the powder flow reproduces the observed linear dependence of the jet height on the concave radius. These findings establish powder jets as a sensitive probe of dissipation in dynamic powder flow and provide a quantitative framework for comparing powder specific interactions such as humidity, particle size and particle shape.