Transportation of Individual Bubble in Diverging Section of Venturi-type Bubble Generator

Flow field and flow parameter, etc., in the diverging section of a Venturi-type bubble generator, are of significance in producing bubbles. A visualized research was consequently carried out on transportation of individual bubbles through a Venturi channel with a rectangular cross section. The analysis shows that dramatic deceleration and deformation of bubbles in the diverging section play a key role in final split or breakup of bubbles. Within a short period about several milliseconds, a bubble in the diverging section always undergoes an increasing deceleration followed by a decreasing deceleration process, during which the bubble also experiences similar manner in rotation process. The maximum rotation velocity of bubbles is about 900-3000 rad/s with the liquid flow rate in the range of 2.4 m³/h to 6.9 m³/h. However, a bubble would keep rotating and being deformed for a certain period of time after its deceleration process ends. The position of a bubble with the maximum rotation velocity lags behind that of maximum deceleration about 2 mm. Liquid flow rate and bubble size have significant effect on the rotation and deformation process. A larger liquid flow rate or a smaller size always incurs a more violent rotation process for a bubble, and the rotation velocity reaches the maximum in the shorter distance. Increasing liquid flow rate aggravates the deformation of a bubble to a certain degree. The visualized research results provide reference and help to illustrate the bubble breakup mechanism, improve the numerical simulation model and optimize the design.