非牛顿流体中气泡行为及其周围流场特性研究

发布时间：2018-06-24 11:55

本文选题：非牛顿流体 + 气泡运动　；参考：《大连理工大学》2016年硕士论文

【摘要】：非牛顿流体中的气泡运动行为广泛存在于石油化工、环境保护、能源开发及利用等工程领域。由于非牛顿流体特殊的流变性质以及气液两相之间相互作用的复杂性,对于非牛顿流体中的单气泡生成、上升以及双气泡聚并行为的研究目前仍不够完善。本文做了以下工作：(1)采用高速摄影技术以及数字图像处理技术对去离子水和不同浓度CMC水溶液中单气泡的生成及上升运动进行实验研究,考察了单气泡的形成过程,讨论了气泡上升过程当量直径、运动轨迹及运动速度的变化规律。研究发现,单气泡的形成过程可细分为三个阶段。在去离子水及CMC水溶液中,气泡的平均当量直径、摆动幅度以及摆动的随机性受喷嘴内径及CMC水溶液浓度的影响较大。在去离子水中,气泡先呈直线上升,当z28mm时,气泡开始振荡,呈螺旋形上升；而在CMC水溶液中,气泡运动轨迹几乎均呈直线。随着CMC水溶液浓度的增加,进气流量的降低,气泡水平速度的波动及气泡垂直速度逐渐减小。随着喷嘴内径的增大,CMC水溶液中气泡水平速度的波动变大,同时高浓度CMC水溶液中气泡的垂直速度也随之增大,但对低粘度溶液中运动气泡的垂直速度的影响并不明显。此外,建立了在一定无量纲参数数值范围内,适用于去离子水与CMC水溶液中,气泡的Rｅ与We、Mo之间的函数关系式。(2)采用FLUENT软件,基于流体体积法(VOF)对单气泡生成及上升运动进行数值模拟,并与实验结果进行对比分析,进而研究气泡周围液相场的特点。研究了单气泡形成过程中气泡及其周围液相压力场和速度场的分布规律,并重点对CMC水溶液中上升气泡周围液相速度场的影响因素进行讨论分析。随着CMC水溶液浓度的升高,气泡周围液体运动速度降低,气泡的影响区减小；而随着进气流量及喷嘴内径的增加,气泡周围液体速度增加,气泡影响区域变宽变长。(3)采用高速摄影对平行双气泡的生长聚并过程进行实验研究并与数值模拟结果对比。结果表明,双气泡的生长及聚并过程可分为四个阶段。重点分析平行双气泡聚并前后气泡纵横比变化的影响因素。气泡聚并之前,气泡纵横比会随着进气流量、喷嘴内径的增加而分别升高和降低。在较低气量、较大喷嘴内径以及大喷嘴间距的情况下,平行双气泡较晚发生聚并。气泡聚并之后,随着进气流量、喷嘴内径的增大及喷嘴间距的减小,气泡纵横比增大,且整个过程中CMC溶液浓度对聚并过程的影响都较为微弱。
[Abstract]:Bubble motion behavior in non-Newtonian fluids is widely used in petrochemical engineering, environmental protection, energy development and utilization. Due to the special rheological properties of non-Newtonian fluids and the complexity of the interaction between gas-liquid phases, the studies on the formation, rise and aggregation of double bubbles in non-Newtonian fluids are still insufficient. In this paper, the following works have been done: (1) the formation and rising motion of a single bubble in deionized water and CMC aqueous solution with different concentrations have been studied experimentally by using high-speed photography and digital image processing technology, and the formation process of single bubble has been investigated. The changes of equivalent diameter, trajectory and velocity of bubble rising are discussed. It is found that the formation process of single bubble can be divided into three stages. In deionized water and CMC aqueous solution, the average equivalent diameter, swing amplitude and randomness of the bubble are greatly affected by the inner diameter of the nozzle and the concentration of CMC aqueous solution. In the deionized water, the bubbles first rise in a straight line, and when the bubbles begin to oscillate, the bubbles rise in a spiral shape, while in the aqueous solution of the z28mm, the trajectory of the bubbles is almost in a straight line. With the increase of CMC aqueous solution concentration and the decrease of inlet air flow rate, the fluctuation of bubble horizontal velocity and bubble vertical velocity gradually decrease. With the increase of nozzle diameter, the fluctuation of the horizontal velocity of bubbles in CMC aqueous solution becomes larger, and the vertical velocity of bubbles in high concentration CMC aqueous solution increases, but the effect on the vertical velocity of moving bubbles in low viscosity solution is not obvious. In addition, a functional relationship between re and Weimo of bubbles in deionized water and CMC aqueous solution in a certain dimensionless parameter range is established. (2) fluent software is used. Based on the fluid volume method (VOF), the formation and rising motion of a single bubble are numerically simulated, and compared with the experimental results, the characteristics of the liquid field around the bubble are studied. The distribution of pressure field and velocity field of liquid phase during the formation of a single bubble is studied, and the factors affecting the velocity field of liquid phase around a rising bubble in CMC aqueous solution are discussed. With the increase of CMC concentration, the velocity of the liquid around the bubble decreases and the influence zone of the bubble decreases, while the velocity of the liquid around the bubble increases with the increase of the inlet air flow rate and the inner diameter of the nozzle. (3) High-speed photography was used to study the growth and coalescence process of parallel double bubbles, and the results were compared with the numerical simulation results. The results show that the growth and coalescence of double bubbles can be divided into four stages. The influence factors of the aspect ratio of the bubbles before and after the parallel double bubbles are analyzed. Before bubble coalescence, the aspect ratio of bubble increases and decreases with the increase of inlet flow rate and nozzle diameter. Under the conditions of lower gas flow, larger nozzle diameter and larger nozzle spacing, the parallel double bubbles converge later. After bubble coalescence, with the increase of inlet air flow rate, the increase of nozzle inner diameter and the decrease of nozzle spacing, the aspect ratio of bubble increases, and the concentration of CMC solution has a weak effect on the coalescence process in the whole process.
【学位授予单位】：大连理工大学
【学位级别】：硕士
【学位授予年份】：2016
【分类号】：TQ021.1

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