文丘里式气泡发生器渐扩段内单气泡输运过程研究

文丘里式气泡发生器渐扩段的流场结构、流动参数等对气泡制备性能起关键作用，因此，对具有矩形截面的文丘里通道渐扩段区域单气泡输运过程进行了可视化研究。分析发现，渐扩段气泡剧烈减速及变形过程对气泡最终的断裂和破碎起关键作用。气泡的减速过程虽只持续数ms时间，依然呈现加速减速和降速减缓两个明显阶段；气泡旋转过程呈现相似的变化规律。在液体流量2.4～6.9 m³/h范围内，对应最大旋转速度可达900～3 000 rad/s。气泡旋转过程持续时间较减速过程稍长，气泡最大旋转速度的位置出现在最大减速加速度位置的下游约2 mm处；液体流量和气泡尺寸对气泡旋转和变形过程有明显影响，液体流量越大或气泡尺寸越小，气泡旋转过程越剧烈，且旋转速度在更短距离内达到最大值；增大液体流量在一定范围内加剧了气泡的拉伸变形。这些可视化研究结果，为进一步揭示文丘里气泡发生装置内气泡的碎化机制、完善数值分析模型、优化设计等提供参考和帮助。

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.