And yet it clogs: bridging of suspensions in constricted channels*

From pipes, to highways, to arteries, stopping the flow is always inconvenient and sometimes dangerous. Clogging can occur whenever a suspension, comprised of discrete particles dispersed in a liquid, flows through a confined geometry. It is a major issue in many engineering systems, such as additive manufacturing or bioengineering but also in irrigation systems and waste management in civil engineering. In this study, we consider the clogging by bridging, i.e., through the formation of a stable arch of particles at a constriction that hinders the transport of particles downstream of the clog. We characterize the role of the volume fraction of particles and of the constriction size on the lifetime of 3D-printed millifluidic devices. Our results show that for small enough constriction and for any solid fraction of particles, the clogging of the system appears to be a matter of when rather than of if. We rationalize our results using a stochastic approach that provides guidelines to avoid clogging by bridging in constricted channels. Understanding the mechanisms and conditions of clog formation can lead to new design principles and to improve the reliability of many engineering systems.