微通道内气泡破裂与界面动力学研究

发布时间：2018-06-17 22:22

本文选题：微流体 + 气泡　；参考：《天津大学》2015年博士论文

【摘要】：近二十年来,新兴的微化工技术得到了迅猛发展。微通道内的气泡行为及动力学是其重要的研究内容之一。本文利用高速摄像仪和高分辨率显微镜实验研究了微通道内气泡的破裂过程。主要内容如下:研究了不对称T型分岔口处的四种不同流型:包括完全阻塞破裂(B1)、部分阻塞破裂(B2)、无阻塞破裂(B3)和不破裂(NB),及其转变机制。完全阻塞破裂与部分阻塞破裂以及部分阻塞破裂与无阻塞破裂之间的转变均可由临界无因次气泡长度描述。与对称T型分岔口相比,本文所采用的不对称结构更易于气泡破裂。研究了不对称T型分岔口处完全受阻塞破裂区域内气泡的破裂过程。实验于宽度为400μm的正方型微通道内进行。气泡在不对称T型分岔口处的破裂过程可分为三个阶段:挤压阶段、过渡阶段和快速夹断阶段。挤压阶段主要受来流速度驱动,连续相粘度的增大可加速颈部变细。在过渡阶段,颈部最小宽度是一个线性变细的过程。在快速夹断阶段,来流速度的作用明显变弱,但其影响仍不可忽略。粘度的增大可减慢该阶段颈部的变细速度。在整个破裂过程中,气泡长度的影响几乎可以忽略。提出了一个可用于预测破裂时间的幂律关联式:0.93/2(/)c c cT T uT w??。研究了对称T型分岔口处气泡的部分阻塞破裂过程。在破裂过程的挤压阶段,在气泡头部和通道壁面之间会有一条表征部分阻塞破裂特点的缝隙出现。气泡和通道壁面之间缝隙的出现对气泡颈部动力学并无明显影响,但是气泡头部的演化过程在缝隙出现前后具有明显差异。通过对头部动力学的分析,探讨了一些对于T型分岔口设计非常重要的参数,例如最终破裂长度和漏液量。研究了十字型分岔口气泡破裂的临界条件。实验结果表明,气泡的临界破裂条件与气泡在十字型分岔口的两个时间尺度——破裂时间和形变时间有关。通过分析气泡通过十字型分岔口时的界面动态演化过程,确定了破裂和形变过程的起始时刻和终了时刻。通过分析各因素对破裂和形变过程的影响,构建了破裂时间和形变时间的数学模型,并得到了气泡破裂的临界条件。
[Abstract]:In the past twenty years, the new micro chemical technology has developed rapidly. The behavior and dynamics of bubbles in the microchannel are one of the important research contents. In this paper, the cracking process of bubbles in microchannels is studied by high speed camera and high resolution microscope. The main contents are as follows: four kinds of asymmetrical T branch branches are studied. Different flow patterns include complete blocking rupture (B1), partial blocking rupture (B2), non blocking rupture (B3) and unruptured (NB), and its transition mechanism. The transition between complete block and partial block rupture and partial block rupture and non blocking rupture can be described by critical dimensionless bubble length. Compared with symmetric T branch, this paper The asymmetric structure is more prone to bubble rupture. The fracture process of the bubbles in the area of the asymmetrical T junction completely blocked and broken is studied. The experiment is carried out in a square microchannel with a width of 400 mu m. The fracture process of the bubbles at the asymmetrical T junction can be divided into three stages: extrusion, transition and rapid clamping. During the transition stage, the minimum neck width is a linear thinning process. In the rapid clamping stage, the effect of the flow velocity is obviously weaker, but its effect can not be ignored. The increase of the viscosity can slow down the thinning speed of the neck at this stage. The effect of the bubble length is almost negligible during the entire fracture process. A power law association can be used to predict the rupture time: 0.93/2 (/) C C cT T uT w?? the partial blocking and breaking process of the bubbles at the symmetric T type fork is studied. In the extrusion stage of the fracture process, there will be a table between the bubble head and the channel wall. There is no obvious effect on the dynamics of the bubble neck dynamics, but the evolution process of the bubble head is obviously different before and after the appearance of the gap. By analyzing the dynamics of the head, some important parameters for the design of the T type fork fork are discussed. For example, the ultimate fracture length and the leakage amount. The critical condition of the fracture of the cross split fork is studied. The experimental results show that the critical fracture condition of the bubble is related to the two time scales of the air bubble in the fork of the fork -- the breaking time and the deformation time. By analyzing the influence of various factors on the rupture and deformation process, a mathematical model of the rupture time and deformation time is constructed, and the critical conditions for the fracture of the bubble are obtained.
【学位授予单位】：天津大学
【学位级别】：博士
【学位授予年份】：2015
【分类号】：TQ021.1

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