Description
Flows of particles through constrictions occur in a broad range of situations, both in nature and in the industry. When the orifice is sufficiently small, clogging can occur, leading to an intermittent or permanent interruption of the discharge. Over the past two decades, extensive work has been conducted to understand the physics and statistics of clog formation. Most of these studies were performed using cylindrical or spherical model particles. However, particles in practical situations often exhibit complex shapes that affect their interactions and flow behavior. In particular, faceted and non-convex particles can interact through multiple contacts, which can strongly influence the probability of clog formation.
Here, we experimentally investigate the role of particle geometry in clogging by studying the flow of dense suspensions of non-Brownian gear-shaped and square-shaped particles in a 2D microfluidic hopper. The particles are fabricated using a photo-lithographic projection method. A PDMS channel is filled with a UV-curable polymer solution and exposed to a UV beam, resulting in the formation of a solid particle. The shape and size of the fabricated particle is controlled by placing a mask on the path of the UV beam. By repeating the fabrication process, the microfluidic channel is filled with hundreds of identical particles. All the particles are then densely packed using a Quake-valve, before being discharged through the channel constriction.
By measuring the average number of particles escaping the channel before a clog forms, we find that interlocked and face-to-face contacts significantly influence the clogging probability. Through systematic shape variations, we show that the clogging probability of gear-shaped particles varies non-monotonically with the fraction of particle surface available for interlocking. This behavior, also reported in other systems of non-convex particles, arises from a competition between the ease of interlocking and the strength of the interlocked contacts. We further demonstrate that the scaling of clogging probability with the outlet-to-particle size ratio deviates from the scaling law reported for circular particles. This deviation is explained by the resistance to rolling due to the multiple contacts between neighboring particles. Experimental results are compared with numerical simulations to gain further insight into the underlying arching dynamics.