Photoelastic precursors to clogging events

Clogging affects countless systems, from microscopic agglomerations in inkjet printers and clots in blood vessels, to large-scale sewer blockages and clogs in silos of grains. Although clogging can be expensive and dangerous, our understanding of the particle scale stress and velocity signatures preceding a clog is currently limited due to experimental challenges.

Here, we study clogs at a fundamental level by closely observing the behaviour of two-dimensional photoelastic particles as they fall through a constriction. In this scenario, a clog occurs when a stable arch of particles forms at the orifice. We use a hopper setup that allows us to tune parameters such as the orifice angle and width. We examine how hopper geometry affects clogging mechanisms and flow regimes. High-resolution imaging techniques and advanced processing methods enable us to quantitatively extract inter-particle forces in the flow before, during, and after a clogging event. Experimental observations indicate the existence of arches that form and break spontaneously, preceding the formation of a stable clogging arch. Our photoelastic force data is used to discern the difference between these different arches. The distribution of forces gives us insight into why stable arches appear and provides a step toward predicting when a clogging event occurs.