Ren Zibo, Zuo Zhigang, Wu Shengji, Liu Shuhong
State Key Laboratory of Hydroscience and Engineering, and Department of Energy and Power Engineering, Tsinghua University, 100084 Beijing, China.
Phys Rev Lett. 2022 Jan 28;128(4):044501. doi: 10.1103/PhysRevLett.128.044501.
The removal of surface-attached particles with cavitation bubbles is usually attributed to the jetting or shear stresses when bubbles collapse. In this Letter, we report an unexpected phenomenon that millimeter-sized spherical particles made of heavy metals (e.g., stainless steel), when initially resting on a fixed rigid substrate, are suddenly accelerated like projectiles through the production of nearby laser-induced cavitation bubbles of similar sizes. We show experimentally and theoretically that the motion of a particle with radius R_{p} is determined by the maximum bubble radius R_{b,max}, the initial distance from the laser focus to the center of the particle L_{0}, and the initial azimuth angle φ_{0}. We identify two dominant regimes for the particle's sudden acceleration, namely, the unsteady liquid inertia dominated regime and the bubble contact dominated regime, determined by R_{b,max}R_{p}/L_{0}^{2}. We find the nondimensional maximum vertical displacement of the particle follows the fourth power and the square power scaling laws for respective regimes, which is consistent with the experimental results. Our findings can be applied to nonintrusive particle manipulation from solid substrates in a liquid.
利用空化气泡去除附着在表面的颗粒通常归因于气泡坍塌时产生的喷射力或剪切应力。在本快报中，我们报告了一种意外现象：由重金属（如不锈钢）制成的毫米级球形颗粒，当最初放置在固定的刚性基板上时，会像抛射体一样突然被附近产生的类似尺寸的激光诱导空化气泡加速。我们通过实验和理论证明，半径为Rp的颗粒的运动由最大气泡半径Rb,max、从激光焦点到颗粒中心的初始距离L0以及初始方位角φ0决定。我们确定了颗粒突然加速的两种主要机制，即非稳态液体惯性主导机制和气泡接触主导机制，这两种机制由Rb,maxRp/L02决定。我们发现，在各自的机制中，颗粒的无量纲最大垂直位移分别遵循四次方和平方比例定律，这与实验结果一致。我们的研究结果可应用于从液体中的固体基板进行非侵入式颗粒操控。
