微通道内非牛顿流体中气泡破裂及聚并行为的模拟研究

发布时间：2018-03-07 23:20

  本文选题：非牛顿流体　切入点：微通道　出处：《天津理工大学》2017年硕士论文　论文类型：学位论文

【摘要】：近年来,随着微流体芯片技术(Lab-on-a-chip)的不断发展,利用微流体技术对微通道内气泡(液滴)的精准调控受到国内外研究者的广泛关注。相比流体体积法(Volume of Fluid,VOF),水平集法(Level Set)和VOF法耦合的(coupled level set and volume of fluid method,CLSVOF)能更加精准地捕获气液界面。本文利用CLSVOF法对微通道内气泡破裂及聚并进行数值模拟研究,研究结果可对微通道反应器的设计和气泡流的精准操作提供理论依据。本文首先通过网格无关性分析及与实验结果对比,验证了该数值方法的有效性,然后选用广泛应用于工业中的羧甲基纤维素钠(CMC)水溶液为非牛顿流体,计算了微通道内该流体中气泡破裂和聚并行为。首先,对四条并行分岔微通道内气泡破裂行为进行研究,模拟结果表明:随u_g/u_l增大,气泡破裂后子气泡依次呈现出长段弹状流、弹状流、泡状流、不阻塞泡状流四种流型;随中间两子通道宽度减小,其中气泡流型由弹状流转变为泡状流,而两侧两子通道由弹状流转变为长段弹状流;随子通道中间分岔角增加,中间子通道由长段弹状流转变为弹状流,而两侧子通道由弹状流转变为长段弹状流;随液相质量浓度的增加,子通道气泡流型出现较长弹状流到弹状流的趋势。另一方面,当u_g/u_l≈1时,气泡均匀破裂,当u_g/u_l增大时,中间子通道子气泡较大;随中间子通道宽度的减小,其中子气泡明显减小,而两侧子气泡增大较快;随子通道中间分岔角增加,中间子气泡减小,而两侧子气泡增大;随液相质量浓度的增加,气泡破裂更为均匀。然后,对部分扩张微通道内气泡聚并行为进行计算,计算结果显示:气泡聚并概率随扩张区域、液相流速、气泡大小、液相质量浓度的增大而增加,但随气泡间距的增加而减小;聚并时间随扩张区域、液相流速、气泡间距的增大而增加,但随液相质量浓度、气泡大小的增大而减小。此外,不等大气泡聚并结果表明:“小追大”情况往往会发生聚并行为,而相反“大追小”则出现二者排斥趋势,不能发生聚并。
[Abstract]:In recent years, with the development of Lab-on-a-chip-chip technology, The precise control of bubbles (droplets) in microchannels by microfluidic technology has attracted wide attention from researchers at home and abroad. Compared with volume of fluid volume of fluid volume, horizontal set and VOF coupled coupled level set and volume of fluid method CLSVOF, the level set method can be more effective than the volume of fluid volume of liquid volume method. In this paper, CLSVOF method is used to simulate the bubble rupture and aggregation in microchannels. The results can provide a theoretical basis for the design of microchannel reactor and the accurate operation of bubble flow. Firstly, the effectiveness of the numerical method is verified by mesh independence analysis and comparison with experimental results. Then, the non-Newtonian solution of CMC (sodium carboxymethyl cellulose), which is widely used in industry, is used as non-Newtonian fluid to calculate the bubble rupture and coalescence behavior in the microchannel. Firstly, the bubble rupture behavior in four parallel bifurcation microchannels is studied. The simulation results show that with the increase of 渭 g / UL, the sub-bubbles show four flow patterns: long slug flow, slug flow, bubbly flow, non-blocking bubbly flow, and decrease with the width of the two sub-channels in the middle. The bubble flow pattern changed from slug flow to bubble flow, while the two sub-channels on both sides changed from slug flow to long slug flow, and the intermediate sub-channel changed from long slug flow to slug flow with increasing bifurcation angle in the middle of sub-channel. On the other hand, with the increase of mass concentration of liquid phase, the bubble flow pattern of sub-channel shows a trend of longer slug flow to slug flow. On the other hand, when uSGP / UL 鈮，

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