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Exclusion zones created by pulsating bubbles in microfluidics

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Under ultrasonic excitation, microfluidic bubbles can create steady flows called streaming. This phenomenon can be useful to create very strong flows in microfluidics, as streaming velocities can reach up to a few millimetres per second for bubbles sizing around 50 microns in diameter.

We show that the interaction between these steaming flows and an external steady flow can create excluded zones, in which the fluid no longer interacts with its surrounding. Using these zones, we suggest that one can trap a known quantity of reactant or particles and then release them in another medium after changing the surrounding fluid. These flows can be simply modeled using hydrodynamic dipoles, thus the shapes and size of these zones can be predicted for any assembly of bubbles, allowing one to tailor-made different geometry of excluded volumes.

View online : Thomas Combriat, Flore Mekki-Berrada, Pierre Thibault, and Philippe Marmottant Phys. Rev. Fluids 3, 013602 (2018)