Chao Cong, Jin Xiaoqiang, Fan Xianfeng
School of Engineering, The University of Edinburgh, The King's Buildings, Robert Stevenson Road, Edinburgh EH9 3JL, U.K.
Langmuir. 2020 Dec 15;36(49):15102-15111. doi: 10.1021/acs.langmuir.0c02679. Epub 2020 Dec 6.
The evolution of thin-liquid films in a microchannel is one of the most critical and intricate phenomena to understand two-phase movement, evaporation, micromixing, heat transfer, chemical synthesis, biological processes, and efficient energy devices. In this paper, we demonstrate experimentally the effect of a liquid film on the removal of an initially dry and lodged bubble in laser-etched poly(methyl methacrylate) microfluidic networks and discuss the evolution of the liquid film in accordance with the bubble superficial velocity and the effect of liquid properties and branch angle on the evolution of the liquid film and the pressure drop. During the removal of a dry bubble, four stages have been observed in the bubble velocity profile and they directly relate to the evolution of the liquid film. The correlation of maximum bubble velocity has been derived as a function of bubble length, fluid viscosity, surface tension, geometry of the cross-sectional area, and dimensions of the microchannel and agrees with the experimental results. The bubble moving distance required for the full deposition of a continuous and stable thin-liquid film is affected by the liquid viscosity and network branch angle. The liquid with a higher viscosity will increase the pressure drop for removing dry bubbles from microfluidic networks, while this effect will be hampered by increasing the microfluidic network complexity. The deposition of the thin-liquid film surrounding bubbles significantly decreases the pressure drop required to remove bubbles from microfluidics. Compared with deionized water, the glycerol solution is prone to acting as the lubricating liquid due to its strong H-bond interaction with the channel wall and the reduction in interfacial energy of the gas-water interface.
微通道中薄液膜的演变是理解两相流、蒸发、微混合、传热、化学合成、生物过程和高效能量装置等过程中最关键且复杂的现象之一。在本文中，我们通过实验证明了液膜对激光蚀刻聚甲基丙烯酸甲酯微流控网络中初始干燥且附着的气泡去除的影响，并根据气泡表观速度以及液体性质和分支角度对液膜演变和压降的影响来讨论液膜的演变。在去除干燥气泡的过程中，在气泡速度分布中观察到了四个阶段，它们与液膜的演变直接相关。已得出最大气泡速度与气泡长度、流体粘度、表面张力、横截面积几何形状以及微通道尺寸的函数关系，且与实验结果相符。连续且稳定的薄液膜完全沉积所需的气泡移动距离受液体粘度和网络分支角度的影响。粘度较高的液体将增加从微流控网络中去除干燥气泡的压降，而增加微流控网络的复杂性会阻碍这种影响。围绕气泡的薄液膜的沉积显著降低了从微流体中去除气泡所需的压降。与去离子水相比，甘油溶液由于其与通道壁的强氢键相互作用以及气 - 水界面界面能的降低，更容易充当润滑液。
