Invited review: Clogging of granular materials in bottlenecks

TL;DR

This review discusses the phenomena of clogging in granular materials at bottlenecks, focusing on statistical distributions, arch formation, and factors influencing flow interruption and resumption.

Contribution

It provides a comprehensive overview of clogging mechanisms, statistical analysis, and future research directions in granular flow through bottlenecks.

Findings

Statistical distributions are key to understanding clogging and unclogging.

Arch structures influence flow interruption and depend on particle shape.

Critical outlet size may exist beyond which clogging does not occur.

Abstract

During the past decades, notable improvements have been achieved in the understanding of static and dynamic properties of granular materials, giving rise to appealing new concepts like jamming, force chains, non-local rheology or the inertial number. The `saltcellar' can be seen as a canonical example of the characteristic features displayed by granular materials: an apparently smooth flow is interrupted by the formation of a mesoscopic structure (arch) above the outlet that causes a quick dissipation of all the kinetic energy within the system. In this manuscript, I will give an overview of this field paying special attention to the features of statistical distributions appearing in the clogging and unclogging processes. These distributions are essential to understand the problem and allow subsequent study of topics such as the influence of particle shape, the structure of the clogging arches and the possible existence of a critical outlet size above which the outpouring will never stop. I shall finally offer some hints about general ideas that can be explored in the next few years.