Department of Chemical Engineering, Illinois Institute of Technology, Chicago, IL 60616, United States of America.
Department of Chemical Engineering, Illinois Institute of Technology, Chicago, IL 60616, United States of America.
Adv Colloid Interface Sci. 2019 Oct;272:101998. doi: 10.1016/j.cis.2019.101998. Epub 2019 Aug 16.
When an air bubble arrives at the free interface, the bubble's lamella drains and ruptures. The bubble collapses, and gas vapor is released. The ruptured lamella retreats, and a rim at the edge of the retreating lamella forms. The rim becomes unstable and breaks into fine droplets, leading to the formation of a mist. As the collapsing bubble gas's vapor is released, the collapsing bubble oscillates and a vertical liquid jet erupts; this jet then breaks into a droplet(s). Here, we present a novel approach for monitoring the air bubble bursting frequency at the air-water interface by the piezoelectric-pressure-acoustic technique. The piezoelectric-acoustic technique monitors the lamella's rupture time, the frequency of the oscillation of the collapsing air bubble, and the frequency of the oscillation at the free air/water interface. The aqueous lamella rupture thickness was probed by reflected light interferometry, and the air bubble burst at the air/water interface was monitored with the high-speed photo imaging technique. The data obtained by the three techniques provided essential information for the stages of the air bubble collapse dynamics at the free interface without the presence of a surfactant. The simple model proposed by Rayleigh, Minnaert, and Lighthill (RML) for the oscillation resonance of a single air bubble was applied to calculate the air bubble collapsing frequency. The floating air bubble bursting frequency with an equatorial radius of 0.33 ± 0.05 cm was well predicted using the air bubble resonance frequency model, and was estimated as 1.0 ± 0.3 kHz. The velocity of the ruptured aqueous lamella covering the air bubble was estimated as 1 m/s. This research presents a comprehensive understanding of the phenomenon of the bare air bubble collapse at the free interface.
当气泡到达自由界面时，气泡的薄液膜会排出并破裂。气泡会塌陷，气体蒸气会被释放出来。破裂的薄液膜会后退，在后退的薄液膜边缘形成一个边缘。边缘变得不稳定并破裂成细液滴，从而形成雾。随着塌陷气泡气体蒸气的释放，塌陷气泡会振荡并喷出一个垂直的液体射流；这个射流随后会分裂成液滴。在这里，我们提出了一种通过压电压力声技术监测气-液界面上气泡破裂频率的新方法。压电声技术监测薄液膜的破裂时间、塌陷气泡的振荡频率以及自由气/水界面的振荡频率。使用反射光干涉法探测水膜破裂的厚度，使用高速摄像技术监测气/水界面上的气泡破裂。这三种技术获得的数据为无表面活性剂存在时自由界面上气泡塌陷动力学各阶段提供了必要的信息。Rayleigh、Minnaert 和 Lighthill (RML) 提出的用于单个气泡振荡共振的简单模型被应用于计算气泡塌陷频率。应用气泡共振频率模型可以很好地预测赤道半径为 0.33 ± 0.05 cm 的浮式气泡的破裂频率，估计为 1.0 ± 0.3 kHz。覆盖气泡的破裂水膜的速度估计为 1 m/s。本研究全面了解了自由界面上裸露气泡塌陷的现象。
