In this paper, we designed a new venturi bubble generator, which mainly consist of two serial rectangular perspex venturi channels with the same geometrical dimension. Visualization experimental method combined with digital image analysis was adopted to study the motion, deformation and breakup process of bubbles when the micro-bubble generator was installed vertically. The bubble foaming frequency which is defined as the amount of forming bubbles within one second from the air injection hole was significantly enhanced with the increase of water flow rate, but was not sensitively affected by the air flow rate. The discrete bubbles moved in a two-stage venturi channel and experienced collapse or breakup in the divergent section. The Sauter mean diameter of bubbles which recorded in each divergent outlet decreased gradually. The Reynolds numbers of water had a significant effect on the breakup characteristics of bubbles. With the increasing of Re, the bubbles experienced binary breakage and multiple breakup successively. Under the effect of complex turbulence vortex, the bubbles presented different breakup patterns in each stage. When Re_th > 19793, the bubble breakup ratio of the first stage divergent section was larger than that of the second stage, and the difference of the generated bubble Sauter mean diameter in each divergent outlet was minimized accordingly. The surface stability of the daughter bubble was enhanced, and it was difficult to breakup significantly under the effect of recirculation flow. The numerical simulation results by Computational Fluid Dynamics (CFD) indicated that the area of the vortex was increased for larger second stage divergent angle, which intensify the phase interaction and promote the possibility of sub-micron bubble breakup.

在本文中，我们设计了一种新型文丘里气泡发生器，主要由两个几何尺寸相同的串联矩形有机玻璃文丘里管组成。采用可视化实验方法结合数字图像分析，研究了微气泡发生器垂直安装时气泡的运动、变形和破碎过程。气泡发泡频率定义为喷气孔1秒内形成气泡的数量随着水流量的增加而显着增加，但不受空气流量的敏感影响。离散气泡在两级文丘里通道中移动，并在发散部分发生坍塌或破裂。在每个发散出口处记录的气泡的Sauter平均直径逐渐减小。水的雷诺数对气泡的破裂特性有显着影响。随着越来越多Re，气泡先后经历了二元破裂和多次破裂。在复杂湍流涡的作用下，气泡在各个阶段呈现出不同的破碎形态。当Re _th  > 19793，第一级发散段的气泡破碎率大于第二级，相应地使每个发散出口产生的气泡Sauter平均直径的差异最小化。子泡的表面稳定性增强，在回流的作用下不易破碎。计算流体动力学 (CFD) 的数值模拟结果表明，随着第二阶段发散角的增大，涡流的面积增加，这加强了相相互作用，促进了亚微米气泡破裂的可能性。