Study of Bubbly and Annular Flow Using Quantitative Flow Visualization

Abstract

Multiphase flow phenomena in bubble columns and annular pipe flow were experimentally studied using quantitative flow visualization. The bubble column work was divided between studies on the operation regime within a sparged bubble column, the effect of vibration on bubble size and void fraction, and the impact of vibration on bubble induced mixing. The operation regime study varied the gas superficial velocity and liquid phase properties and then analyzed the impact on the bubble size distribution and void fraction to identify operation regimes. This study showed that increasing the liquid viscosity enhances the regime transition from homogeneous to heterogeneous. In addition, bubble size was successfully scaled in the heterogeneous regime showing that it has an inverse power-law correlation with the scaled specific input power. The vibration study used a single point injector and measured the bubble size distribution and void fraction with high-amplitude (up to 10 mm), low-frequency (< 23 Hz) vibrations. A power-law correlation between the scaled bubble size and scaled specific input power was identified. The bubble induced mixing study tracked the distribution of a passive scalar within a sparged bubble column exposed to vibrations in the aforementioned range. These results show that vibration suppresses the liquid velocity agitations in the bubble swarm wake, which decelerates mixing, while also bubble clustering and aggregation produces void fraction gradients that induce a mean flow that accelerates mixing. Finally, the annular pipe flow work used planar laser induced fluorescence to study the sensitivity of the annular film thickness on the bottom of the pipe to inclination angle. The current measurements were first validated by comparing the results in horizontal (pipe) orientation with established data from the literature. The horizontal results also showed that the ratio of the film roughness to film thickness increases with increasing liquid flow rate. Then the pipe inclination angle was varied from 20 degrees (downward) to +60 degrees (upward). The downward results show the film thickness decreasing with increasing inclination angle, while the upward results have the film thickness remain relatively constant. However, the upward results did show that the film thickness had significant temporal fluctuations.