Investigations of particle dynamics and their interaction with the carrying flow in micro systems
Final Report Abstract
The project has first studied the statistics of clogging in a constricted suspension flow, in an experimental model system in which solid particle-particle and particle-wall contacts were practically absent. In this condition, clogging can only occur by the formation of an arch blocking the constriction. Surprisingly, our results concluded that the arch formation in suspensions follows Poissonian statistics, in the same way as granular (dry) noncohesive particles do, and that one can reach a continuous flow independently of the particle concentration in a wide range of relative particle sizes. A statistical model was developed which predicts the average number of particles that would be able to pass the constriction before an arch is formed. This can be easily transformed into a functioning/flowing time for a given particle flux. Due to the Poissonian statistics, we can nearly predict the infinite flowing times for a wide range of particles sizes and geometries. In order to improve the performance of suspensions in confined systems, we studied the effect of acoustic forces on the clogging statistics. The system was designed to apply a force that would slowly drag particles to the center of the channel, reducing the probabilities of forming an arch at the constriction, and hindering the clogging probability. Although the experimental results are positive, above certain acoustic excitation amplitude, the clogging statistics become comparable to the case with no acoustic assistance. We hypothesize that this decrease in performance is related with the close proximity to each other at which the particles are being dragged by the acoustic forces, producing a significant amount of solid (permanent) clusters that would favor the arch formation. The project considered the motion of non-Brownian spherical particles in a straight channel with a Hele-Shaw (quasi-2D) geometry under viscous-dominated flow conditions. Surprisingly, when a low concentration of particles is loaded in the system, the particles trajectories are observed to twist, curve and even entangle with each other. Using experiments and particle dynamics simulations, we reveal that the rich complexity in the particle dynamics is due to the dominance of short-range particle-particle and particlewall hydrodynamic interactions, resulting in a very good quantitative comparison between experiments and numerical simulations.
Publications
-
Clogging in constricted suspension flows, Physical Review E 97 (2), 021102, (2018)
A. Marin, H. Lhuissier, M. Rossi, C.J. Kähler
