Study Of Single Bubble Breakup In Stirred Tank

Bubble motion and breakup behavior have significant effects on the transfer process of two-phase flow in most gas-liquid reactors,because bubble is the dispersed phase among them.The main research content of this paper is motion and breakup process of single bubble behind Rushton turbine blade in stirred tank.High-speed camera technology and 2D-PIV technology are used respectively to study bubble behavior.The causes of bubble breakup at critical stirring rate are explored by analyzing the breakup behavior of bubbles at different stirring rates,combined with flow field structure behind blade,High-speed camera was used to measure the movement and breakup process of single bubble under different experimental conditions,which equivalent diameter ranging from 2.7 mm to 3.3 mm.With the increase of stirring rate,the breakup probability of bubbles increases,the number of daughter bubbles in first breakup increases,and the bubble breakup time decreases.The critical stirring power of bubble breakup is 0.47 W·kg-1 in this experiment.Single-phase liquid flow field without bubble at critical stirring rate was obtained by 2D-PIV technique.It is found that shear rate in part of the area behind blade is larger when the blade is near the entrance of bubbles by analyzing the single-phase flow field,and the range of liquid velocity,turbulent kinetic energy ratio,turbulent kinetic energy dissipation ratio and capillary number in bubble breakup concentrated area is obtained.Flow field on the trajectory of the bubble shows that bubble must interact with liquid phase for some time before breakup.Turbulent kinetic energy,turbulent kinetic energy dissipation rate and shear rate of liquid phase increase along the bubble trajectory and reach the maximum value during bubble movement behind the blade.By measuring the liquid flow field in the presence of bubble with 2D-PIV technique,we found the maximum liquid velocity around bubble before breakup decreased relative to that when the bubble entered the flow field,while the maximum energy dissipation rate and shear rate of turbulent flow increased significantly.The critical shear rate of the surrounding liquid phase is 1008 s-1 at bubble breakup moment.Energy of liquid phase in turbulent flow field is transferred to bubble and accumulated in it during bubble movement,and the total energy reaches a critical value before bubble breakup.Then bubble is broken by instantaneous high turbulent flow energy dissipation rate or strong shear in liquid phase.