Acoustic Anti-Clogging Effect in Microfluidic Constrictions: Can Clogging Be Reduced by Simply Redistributing Particles?

Forcing stuff through narrow constrictions leads inevitably to clogging. Regardless the system we are dealing with: grains in silos, particles through funnels, crowds through narrow exits, or in our case, a suspension through a microfluidic constriction. Finding methods to influence and eliminate the clog formation is not only of crucial importance to improve the mass transfer in industrial systems, but also to save lives when dealing with crowds. In this work we study the effect of ultrasound actuation on a diluted suspension passing through a very narrow microfluidic constriction (from 1 up to 2 particle diameters). A standing acoustic wave with a central node in the middle of the channel induces acoustic radiation forces on the suspended particles, leading to particle migration towards the center of the channel. But, is this transversal particle redistribution -- caused by the acoustic radiation force-- enough to cause a substantial improvement of the mass transfer? We will present experimental and numerical results that confirm that, although ultrasound actuation indeed has a great influence on the performance of the microfluidic hourglass, the particle redistribution around the center of the channel plays only a minor role in the prevention of clogs.