【作者】 姜韶堃；

【导师】 马友光；

【作者基本信息】 天津大学 ， 化学工程， 2007， 博士

【摘要】 非牛顿流体中的气泡行为是诸多实际化工过程的基础。本文实验研究了非牛顿羧甲基纤维素钠(CMC)溶液中的单气泡生成、上升以及连续气泡的聚并现象,并进行了相应的理论分析。采用激光显影成像技术结合CCD照相方法研究了液相中单喷嘴单气泡的生成行为。与传统照相技术相比,该法能够获得清晰的二维气泡放大图像。实验结果表明,气泡生成大致可以分为两个阶段,第一阶段,主要受径向扩张控制,第二阶段,纵向拉伸运动占明显优势。此外,还研究了溶液流变性质、气室体积和喷嘴直径等因素对气泡分离体积和气速之间关系的影响。利用激光多普勒测速仪测定了气泡上升过程中其周围流体的流场分布。结果表明液相轴向和径向时均速度分别随着轴向和径向位置变化体现出特定的规律。统计分析得到,气泡周围液相轴向和径向产生了非均衡的湍动效应,并且气泡生成区域的液相扰动要比气泡上升区域更剧烈一些。采用傅立叶分析和小波方法等时频分析技术对液相中单点瞬时速度时间序列进行研究,功率谱图中的特征峰证明实验气速条件下的气泡上升运动存在着一定的周期性规律;功率谱低频宽峰、局部间歇测度和小波能量分布都表明液相流场中存在着特定的涡流结构。针对非牛顿流体中的气泡上升及连续聚并现象进行了气泡通过时间序列采样,采用时频分析技术、混沌理论及分形理论展开讨论。当聚并现象发生后,功率谱分析表明气泡由准周期运动发展为混沌运动,各小波尺度能量随着高度和气速分布也体现出特定的规律。关联维数的非整数特征和最大Lyapunov指数均大于0表明气泡上升及聚并过程是确定性的混沌运动,并且具有较高的复杂度,通过最大Lyapunov指数还可以对聚并程度做近似判断。R/S分析表明,气泡上升及聚并过程具有明显的双分形特征,受到正持久性和反持久性两种动力学因素制约。更多还原

【Abstract】 Bubble behavior in non-Newtonian fluids is of great importance for practical production in chemical industry. In this thesis, experiments were conducted to investigate the formation and rising of a single bubble and coalescence of successive bubbles in non-Newtonian fluids of Carboxymethylcellulose sodium (CMC) polymer. Theoretical analyses were also made to reveal the characteristics of bubble movement.Laser image visualization technique, combined with photograph method by CCD, was employed to study single bubble formation at a submerged orifice in liquid phase. The photographs show that magnified two-dimensional bubble images can be obtained clearly. The experimental results show that bubble growing process can be divided into two stages: in the first stage, bubble growth is mainly controlled by the radial expansion, but in the second stage, axial elongation dominates the process. In addition, the effects of rheological properties of solution, reservoir volume and orifice diameter on the relation between bubble detached volume and gas flowrate were investigated experimentally.Laser Doppler velocimetry was used to measure the mean velocity field in liquid phase around the bubble during its rising process. It indicates that axial and radial mean velocities along the directions of axis and radius exhibite characteristic distribution trends, respectively. Anisotropic turbulence was found by statistical analysis, and fluctuations of liquid in the bubble formation area were more violent than that in the bubble rising area. Instantaneous velocity time series were analyzed by applying Fourier analysis and Wavelet method. Power spectrum reveals that the rising of bubbles behaves some certain periodic rule under the conditions of experimental gas flowrates, and the wide peaks in the low-frequency area of power spectrum, local intermittency measure and wavelet energy profile imply the existence of vortex with certain structures in liquid near bubbles.Time series on bubble passage for successive rising and coalescence of bubbles were collected and analyzed by making use of time-frequency analysis, chaos theory and fractal theory. As coalescence occurred, power spectrum showed that bubbles rose from approximately periodic movement to typical chaos and the variation of wavelet scale energy with heights and gas flowrates, respectively, also represented specified regularity. Non-integral correlation dimensions and positive largest Lyapunov exponents proved that the rising and coalescence of bubbles were deterministic chaos with great complexity, and coalescence extent could be estimated with largest Lyapunov exponent. Furthermore, R/S analysis manifested double fractal characteristics which meant that the rising and coalescence of bubbles were controlled by persistence and anti-persistence dynamics.更多还原