The interest in application of ultrasonic cavitation for cleaning and surface treatment processes has increased greatly in the last decades. However, not much is known about the behavior of cavitation bubbles inside the microstructural features of the solid substrates. Here we report on an experimental study on dynamics of acoustically driven (38.5 kHz) cavitation bubbles inside the blind and through holes of PMMA plates by using high-speed imaging. Various diameters of blind (150, 200, 250 and 1000 µm) and through holes (200 and 1000 µm) were investigated. Gas bubbles are usually trapped in the holes during substrate immersion in the liquid thus preventing their complete wetting. We demonstrate that trapped gas can be successfully removed from the holes under ultrasound agitation. Besides the primary Bjerknes force and acoustic streaming, the shape oscillations of the trapped gas bubble seem to be a driving force for bubble removal out of the holes. We further discussed the bubble dynamics inside microholes for water and Cu²⁺ salt solution. It is found that the hole diameter and partly the type of liquid media influences the number, size and dynamics of the cavitation bubbles. The experiments also showed that a large amount of the liquid volume inside the holes can be displaced within one acoustic cycle by the expansion of the cavitation bubbles. This confirmed that ultrasound is a very effective tool to intensify liquid exchange processes, and it might significantly improve micro mixing in small structures. The investigation of the effect of ultrasound power on the bubble density distribution revealed the possibility to control the cavitation bubble distribution inside the microholes. At a high ultrasound power (31.5 W) we observed the highest bubble density at the hole entrances, while reducing the ultrasound power by a factor of ten shifted the bubble locations to the inner end of the blind holes or to the middle of the through holes.

在最近的几十年中，将超声波空化应用到清洁和表面处理过程中的兴趣大大增加了。然而，对于固体基质的微结构特征内部的气穴气泡的行为了解甚少。在这里，我们使用高速成像技术对PMMA板的盲孔和通孔内的声驱动（38.5 kHz）空化气泡动力学进行了实验研究。研究了各种直径的盲孔（150、200、250和1000 µm）和通孔（200和1000 µm）。在基材浸入液体中时，气泡通常会被捕获在孔中，从而阻止其完全润湿。我们证明了在超声搅拌下可以成功地从孔中清除截留的气体。除了主要的Bjerknes力和声流，被捕获的气泡的形状振荡似乎是从孔中去除气泡的驱动力。我们进一步讨论了水和铜的微孔内部的气泡动力学²⁺盐溶液。已经发现，孔的直径以及部分液体介质的类型会影响空化气泡的数量，大小和动力学。实验还表明，通过空化气泡的膨胀，孔内的大量液体可以在一个声波循环内被置换。这证实了超声是强化液体交换过程的非常有效的工具，它可能会显着改善小型结构中的微混合。超声功率对气泡密度分布影响的研究表明，可以控制微孔内部的空化气泡分布。在高超声功率（31.5 W）下，我们观察到孔入口处的气泡密度最高，