Flow of dense suspensions through a quasi-bidimensional constriction: particle dynamics and self-filtering

Understanding the extrusion of suspensions of particles through nozzles and constrictions is important for manufacturing applications as the composition of the extruded material can be significantly affected by the process and, as a result, different from the initial suspension in the reservoir. We investigate experimentally the flow of a dense suspension of non-Brownian particles through a constriction of controlled width in a quasi-bidimensional channel. We also systematically vary the angle of the constriction, studying both slightly tapered and hopper-like channels. We analyze the discharge by imaging the particles crossing the constriction per unit time, evaluating the local volume fraction, and characterizing the particle velocity profile at the outlet. Our experiments show that while the discharged solid fraction can be well-predicted at sufficiently large constriction widths, self-filtration is observed when decreasing the width of the constriction. The results are compared to the discharge of dry grains in a model silo, and a common framework is developed to predict the predict the behavior of particles when varying the geometry of the system.