Numerical Study on the Vapor Bubble Removal by Acoustic Streaming in Downward-Facing Pool Boiling

The dynamic mechanism of vapor bubble removal by acoustic streaming on downward-facing heating sur-face during boiling process was numerically investigated. It is observed that under the excitation of longi-tudinal surface acoustic wave (SAW), vortices are formed at the root of bubble due to acoustic streaming. The vortices promote the bubble to detach from heating surface, while inhibiting the lateral growth and movement of the bubble. Thus, the bubble can be suspended in the liquid, almost statically. In addition, under the excitation of the transverse SAW, the generated vortices produce a translational thrust on the bubble, causing the bubble to move laterally and eventually leave the heating surface. For the case of su-perimposed SAWs excitation, the transverse SAW breaks the balance of vortical flow around the bubble which initially excited by the longitudinal SAW. Meanwhile, the unbalanced vortices destroy the boundary layer of heating surface, and weaken the influence of the viscous force as well. The results show that un-der the superimposed SAWs excitation, comparing with transverse SAW solely, the time for the bubble to detach laterally from the downward-facing heating surface is shortened by nearly 33%, and the removal speed of the bubble is also increased by nearly 45%. It indicates that SAW excitation can serve as an effective approach for active control and enhancement of boiling heat transfer on the downward-facing heating surface.(c) 2022 Elsevier Ltd. All rights reserved.