【作者】 张菊；

【导师】 刘志军；

【作者基本信息】 大连理工大学 ， 化工过程机械， 2016， 硕士

【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z>28mm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。更多还原

【Abstract】 Bubble behavior in non-Newtonian fluids is widely used in petrochemical industry, environmental protection, energy development and utilization and so on. Due to the complexity of the rheological properties of non-Newtonian fluids and the interaction between gas-liquid, the research on the motion of single bubble and the bubble coalescence is still not perfect. The following work has been done:(1) Formation and the ascending motion of a single bubble in deionized water and carboxymethyl cellulose (CMC) solution was experimentally investigated by high speed photography and digital image processing technique. The bubble diameter, trajectory and the velocity were discussed and the process of bubble formation was studied. The results showed that the process of the formation of the bubble can be divided into three stages. The average equivalent diameter and the oscillation were greatly affected by the diameter of the nozzle and the concentration of the solution in deionized water and CMC aqueous solution. In deionized water, the bubble rose straight up initially, when z>28 mm, the bubble began to oscillate with a helical path while the trajectory of the bubble was almost linear in CMC aqueous solution. With the solution concentration increasing and the gas flow decreasing, the fluctuation of the horizontal velocity and the value of the vertical velocity of the bubble decreased. The influence of the diameter of the nozzle on the vertical velocity is not obvious in CMC aqueous solution with low concentration, but the fluctuation of the horizontal velocity and the value of the vertical velocity of the bubble in CMC aqueous solution with high concentration increased by the increase of the diameter of the nozzle. In addition, the correlations between Re, We and Mo respectively in deionized water and CMC aqueous solution were proposed.(2) Based on the volume of fluid (VOF) a numerical simulation was performed to study the formation and the movement of single bubble in FLUENT to investigate the characteristics of liquid phase field and compared with the experimental results. The pressure and the velocity field of the liquid around the bubble were analyzed during the bubble formation and more attention is paid to the study of the influence factor of the liquid velocity field during the rise of the bubble. With the increase of the concentration of the CMC aqueous solution, the velocity of the liquid around the bubble decreased and the deeply influenced region narrowed. And the velocity of the liquid increased with the increase of gas flow and the diameter of nozzle, while the deeply influenced region was broaden and lengthened.(3) The growth and coalescence process of parallel double bubble were experimentally investigated by high speed camera that were compared with the numerical simulation results. The results showed that the whole process of the bubble growth and coalescence was divided into four stages. And more attention is paid to the study of the influence factor of the bubble aspect ratio before and after the bubble coalescence. Before the bubble coalescence, the aspect ratio increased with the gas flow increased and decreased with the diameter of nozzle increased. The bubble coalescence occurred later at the lower gas flow, the larger diameter of the nozzle and the larger spacing of the nozzles. After the bubble coalescence, with the increase of the gas flow and the diameter of the nozzle and the decrease of the nozzle spacing, the aspect ratio increased, but the influence of CMC solution concentration on the aspect ratio was relatively weak.更多还原