Emptying bottles filled with suspensions

This work investigates, based on laboratory experiments, the influence of particles on the drainage of a bottle filled with an isodense suspension. Similarly to the drainage of a pure liquid, the flow rate remains constant during the whole emptying process and is primarily controlled by the size of the exit hole. Despite a hole-to-particle size ratio that would normally promote clogging, no such events are observed due to the periodic entrainment of air bubbles. The presence of particles causes a slight decrease in flow rate when increasing the particle initial packing fraction. Even for initial packing fractions of up to 60 %, it only decreases by at most 20 %. Revisiting the model of Clanet & Searby (2004) J. Fluid Mech . 510 , 145–168, the flow rate is found to be linked to the rise velocity of the bubbles, which is surprisingly nearly independent of the packing fraction, even for values as high as 60 %. This counterintuitive result suggests that the suspension becomes heterogeneous, with a particle-depleted region in the pathway of the bubbles. Moreover, during drainage, the suspension exiting the bottle has a smaller packing fraction than the initial suspension, leading to an accumulation of particles inside the bottle and therefore an increase in the global packing fraction inside the vessel. When this latter reaches a critical value close to random loose packing, particles start to emerge above the liquid free surface. Based on accurate measurements that enable the computation of the mean packing fraction at all times, a model is proposed to describe this transition.