Department of Mechanical Engineering, Nanjing University of Science and Technology , Nanjing, Jiangsu, China.
J Phys Chem B. 2013 Oct 17;117(41):12549-55. doi: 10.1021/jp404886h. Epub 2013 Oct 7.
When subjected to an ultrasonic standing-wave field, cavitation bubbles smaller than the resonance size migrate to the pressure antinodes. As bubbles approach the antinode, they also move toward each other and either form a cluster or coalesce. In this study, the translational trajectory of two bubbles moving toward each other in an ultrasonic standing wave at 22.4 kHz was observed using an imaging system with a high-speed video camera. This allowed the speed of the approaching bubbles to be measured for much closer distances than those reported in the prior literature. The trajectory of two approaching bubbles was modeled using coupled equations of radial and translational motions, showing similar trends with the experimental results. We also indirectly measured the secondary Bjerknes force by monitoring the acceleration when bubbles are close to each other under different acoustic pressure amplitudes. Bubbles begin to accelerate toward each other as the distance between them gets shorter, and this acceleration increases with increasing acoustic pressure. The current study provides experimental data that validates the theory on the movement of bubbles and forces acting between them in an acoustic field that will be useful in understanding bubble coalescence in an acoustic field.
当处于超声驻波场中时，小于共振尺寸的空化泡会迁移到压力波腹处。当气泡接近波腹时，它们也会相互靠近，并形成一个簇或聚结。在这项研究中，使用高速摄像机的成像系统观察了在 22.4 kHz 的超声驻波中两个相互靠近的气泡的平移轨迹。这使得可以测量比先前文献中报道的更接近的距离处的接近气泡的速度。使用径向和平移运动的耦合方程对两个接近的气泡的轨迹进行了建模，结果与实验结果具有相似的趋势。我们还通过监测在不同声压幅度下气泡接近时的加速度，间接地测量了二次 Bjerknes 力。当它们之间的距离变短时，气泡开始相互加速，并且这种加速度随着声压的增加而增加。本研究提供了实验数据，验证了在声场中气泡运动和作用于它们之间的力的理论，这对于理解声场中的气泡聚结将是有用的。
