Jetting dynamics associated with bubble formation during acoustic levitation

Jetting is a ubiquitous phenomenon that has significant applications in industries, which is often generated by the rupture of bubbles in the liquid phase. Here, we investigate the jetting dynamics of an acoustically levitated droplet during the drop-to-bubble transition by using high-speed imaging. Our results show that jetting occurs during bubble formation rather than during rupture. Both viscosity and surface tension are found to significantly influence the jetting process. Specifically, as viscosity increases, both the upward and downward jetting velocities decrease, while an increase in surface tension results in higher jetting velocities in both directions. Furthermore, finite element simulations of the ultrasonic field reveal that the downward-moving liquid experiences a stronger acoustic radiation force compared to the upward-moving liquid. During the movement of the jet, the downward jetting experiences a stronger suppression force than the upward jetting. This distinct force distribution results in a higher upward jetting velocity than downward jetting velocity. This study offers new insights into the interaction between an acoustic field and jetting dynamics, thereby providing a novel method for generating jets without cavitation.