Bubble Behavior In Non-Newtonian Fluids

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.