Laboratory Experiments on Agglomeration of Particles in a Granular Stream

TL;DR

This study investigates how particle shape and adhesion influence agglomeration in granular streams through laboratory experiments, revealing irregular particles form larger and more easily formed agglomerates than spherical ones, with implications for planetary surface features.

Contribution

The paper introduces a new statistical method for measuring particle adhesion and compares agglomeration behaviors of spherical and irregular particles in granular streams.

Findings

Irregular particles form larger agglomerates than spherical particles.

Irregular particles agglomerate more easily at similar velocities and adhesion levels.

Agglomerate size and degree can indicate particle shape and adhesion properties.

Abstract

Inelastic collisions occur among regolith particles, such as those in the ejecta curtain from a crater, and may cause clustering or agglomeration of particles and thus produce discrete patterns of ejecta deposits around a crater. Previous studies have shown that clusters, and even agglomerates, are formed via mutual, inelastic collisions of spherical particles due to adhering forces between particles in granular streams. To investigate the condition of agglomerate formation in granular streams, we conducted laboratory experiments of granular streams using both spherical and irregular, non-spherical particles. Measurements of particle adhesion in this study were performed using a centrifugal separation method, in contrast to the previous study in which atomic force microscopy (AFM) was used. This enabled simultaneous measurements of multiple particles of various shapes for a statistical analysis of the results. With similar relative velocities and adhesion values, irregular particles were found to form agglomerates much more easily than spherical particles. The axial ratio of the agglomerates of spherical particles and irregular particles was similar and was in accordance with those observed in previous laboratory studies, whereas the size of the agglomerates of irregular particles was larger than the size of spherical particles. The degree of agglomeration and the size of agglomerates can be used as an indicator of the shape or adhesive force of the particles in granular stream. Our findings on agglomeration in granular streams could provide new insights into the origin of rays on airless bodies and grooves on Phobos.