Time-resolved velocity and pressure field quantification in a flow-focusing device for ultrafast microbubble production

TL;DR

This study investigates the rapid velocity and pressure fluctuations within a flow-focusing device during microbubble production, combining experimental measurements and numerical modeling to understand oscillatory behaviors at microsecond and nanosecond scales.

Contribution

It provides the first detailed quantification of velocity and pressure oscillations in flow-focusing nozzles at nanosecond resolution, linking these to bubble pinch-off dynamics.

Findings

Velocity oscillations propagate at microsecond scales.

Pressure oscillations linked to bubble pinch-off occur at nanosecond scales.

Experimental and numerical results agree on oscillation characteristics.

Abstract

Flow-focusing devices have gained great interest in the past decade, due to their capability to produce monodisperse microbubbles for diagnostic and therapeutic medical ultrasound applications. However, up-scaling production to industrial scale requires a paradigm shift from single chip operation to highly parallelized systems. Parallelization gives rise to fluidic interactions between nozzles that, in turn, may lead to a decreased monodispersity. Here, we study the velocity and pressure field fluctuations in a single flow-focusing nozzle during bubble production. We experimentally quantify the velocity field inside the nozzle at 100 ns time resolution, and a numerical model provides insight into both the oscillatory velocity and pressure fields. Our results demonstrate that, at the length scale of the flow focusing channel, the velocity oscillations propagate at fluid dynamical time scale (order of microseconds) whereas the dominant pressure oscillations are linked to the bubble pinch-off and propagate at a much faster time scale (order of nanoseconds).