Department of Mechanical Systems Engineering , Tokyo University of Agriculture and Technology , Nakacho 2-24-16 , Koganei , Tokyo 184-8588 , Japan.
Department of Chemical and Materials Engineering, Faculty of Engineering , University of Alberta , Edmonton , Alberta T6G1H9 , Canada.
Langmuir. 2018 Apr 10;34(14):4234-4240. doi: 10.1021/acs.langmuir.8b00246. Epub 2018 Mar 28.
We investigate the enhancement of the velocity of focused liquid jets by surface bubbles preformed on the inner surface of the container. The focused jets are created from the impact on a liquid-filled cylindrical tube at cavitation numbers of 0.37 (strong impact where cavitation is likely to occur on unprocessed surfaces) and 2.1 (weak impact where cavitation does not occur from the impact). The bubbles with a base diameter up to hundreds of micrometers were formed via the process of solvent exchange using air-equilibrated ethanol and water. Our measurements by high-speed imaging show that at both cavitation numbers, the jet velocities with preformed bubbles are significantly higher than those without preformed bubbles. Furthermore, our results show that after the process of solvent exchange, a large number of expanding bubbles are observed at cavitation number of 0.37, indicating that possibly both sub-millimeter and sub-micrometer bubbles on the surface contribute to the jet velocity enhancement. At the cavitation number of 2.1, the surface bubbles are observed to oscillate immediately after the impact. The measurements of the liquid pressure after the impact reveal that at both cavitation numbers, the negative pressure is damped by the preformed surface bubbles, contributing to the increase of the jet velocity. This work sheds light on the crucial role of surface bubbles on the impulsive motion of liquids. Our findings have significant implications for the focusing jet technology, opening the opportunities for jetting fragile samples such as biological samples.
我们研究了通过在容器内表面预先形成的表面气泡来增强聚焦液体射流的速度。聚焦射流是通过在空化数为 0.37（强冲击，可能在未经处理的表面发生空化）和 2.1（弱冲击，冲击时不会发生空化）的充满液体的圆柱管上的冲击产生的。直径达数百微米的气泡是通过使用空气平衡的乙醇和水进行溶剂交换过程形成的。我们的高速成像测量结果表明，在这两种空化数下，带有预先形成的气泡的射流速度明显高于没有预先形成的气泡的射流速度。此外，我们的结果表明，在溶剂交换过程之后，在空化数为 0.37 时观察到大量膨胀的气泡，这表明表面上的亚毫米和亚微米气泡可能都有助于射流速度的提高。在空化数为 2.1 时，表面气泡在冲击后立即观察到振荡。冲击后液体压力的测量结果表明，在这两种空化数下，预先形成的表面气泡都会使负压衰减，从而导致射流速度增加。这项工作揭示了表面气泡对液体脉冲运动的关键作用。我们的发现对聚焦射流技术具有重要意义，为喷射脆弱样品（如生物样品）提供了机会。
