受限管道内移动气泡的液膜界面形貌研究
INTERFACE MORPHOLOGY OF MOVING BUBBLES IN CONFINED CHANNELS
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摘要: 受限管道中的气泡移动在诸如二氧化碳填埋与驱油、心脑血管和肺部气液输运等领域具有重要的应用, 液膜动力学以及气-液界面的形貌演变这些关键问题受到关注. 文章旨在通过基于光干涉的实验方法, 探究气泡在受限管道内移动过程中, 气体与管壁间的液膜相对厚度分布, 并分析其变化规律, 得到周期性变速移动气泡引起的液膜厚度特征. 通过液滴微流控的流动聚焦法, 分别在蛇形延长管道和平直短管道内形成了匀速移动的气泡和变速移动气泡. 利用绿色光在气-液和液-固界面产生的两道反射光之间干涉所形成的条纹, 通过相对光干涉强度(ROII)方法得到液膜厚度分布. 发现在与气泡固连的参考系中, 匀速移动气泡引起的液膜厚度呈稳态分布, 且得到了与以往的研究工作相符的、接近气泡尾部的马鞍形厚度分布, 证明了该实验方法的有效性. 在气泡进行周期性减速—加速—匀速的移动过程中, 气泡参考系内的液膜厚度呈现了随时间周期性变化的厚度分布. 气泡加速与减速均引起了界面形貌的整体变化, 且体现出了滞后性. 本研究发现了变速移动气泡特殊的液膜厚度演变规律, 将为针对受限管道内气泡的理论和计算研究提供实验观测的依据.Abstract: Bubble motion in confined channels has important applications in such fields as carbon dioxide landfill and oil displacement, cardio-cerebrovascular and pulmonary gas-liquid transport. Key issues such as liquid film dynamics and the morphology evolution of the gas-liquid interface have drawn much attention. The purpose of this work is to explore the relative thickness distribution of the liquid film between gas and solid wall, by an experimental method based on light interference, during the motion of bubbles in a confined channel. In particular, we aim to identify the characteristics of liquid film thickness caused by periodically varying speed of bubbles. In the experiments, steadily moving bubbles and bubbles with accelerations were formed in a snake-shaped long channel and a straight short channel, respectively, by the flow-focusing method of droplet microfluidics. The relative optical interference intensity (ROII) method was used to obtain the thickness distribution of the liquid film by analyzing the fringes, which are formed by the interference between two beames of reflected lights at the gas-liquid and the liquid-solid interfaces, respectively. Our findings indicate that the liquid film caused by bubbles moving at a constant velocity shows a steady thickness distribution in the bubble’s moving reference frame, and a saddle-shaped thickness distribution at the rear of the bubble is obtained, which proves the validity of the experimental method. On the contrary, when the bubble undergoes periodic deceleration - acceleration - constant speed motion, the thickness distribution of the liquid film in the bubble’s moving reference frame changes periodically with time. The varying speed of bubbles causes the overall temporal evolution of the gas-liquid interface morphology and shows a hysteresis effect. This study of the liquid film thickness at varying speed of bubbles may provide phenomena and experimental data for theoretical and computational study on the bubble dynamics in confined geometries.