The Study Of Bubble Behaviors And Ambient Flow Field In Non-Newtonian Fluid

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.