轴向旋流式微气泡发生器的结构设计与数值模拟

Structural design and numerical simulation of axial-swirling type micro-bubble generator

设计了一种旋流式微气泡发生器,由环形注气机构和新型气泡破碎机构两部分组成,前者采用中心圆环＋微孔板结构,后者由静止起旋元件和文丘里管组成,采用ANSYS FLUENT软件对新型气泡破碎机构的流道进行数值模拟,并与常规文丘里流道对比.结果表明,新型气泡破碎机构流道内的水流速度、径向速度梯度、湍动能和湍能耗散率均大于常规文丘里流道,常规文丘里流道出口处产生的微气泡直径为新型气泡破碎机构的2倍.采用响应曲面法优化静止起旋元件结构,优化后的叶片出口角度为35？,中心圆柱体直径为12.3 mm,叶片长度为10 mm,优化后的气泡破碎机构产生的微气泡直径为优化前的75%.

A swirling-type micro-bubble generator was designed in this paper. The main structure of swirling-type microbubble generator consisted of annular gas injection mechanism and new-type bubble breaking mechanism. Among this, the annular gas injection mechanism adopted the structure of ＂center ring＋micro-plate＂. The new-type bubble breaking mechanism was composed of the static swirl element and the venturi tube. The static swirl element was coaxially set in the inlet section of venturi tube. Compared with traditional venturi tube, the newtype bubble breaking mechanism had some technical advantages and may produce much smaller microbubbles. With the help of ANSYS FLUENT software, the numerical simulation of the flow path of the new bubble breaking mechanism was carried out and compared with the conventional venturi flow path. The simulation results showed that the velocity, radial velocity gradient, turbulent kinetic energy and turbulent dissipation rate in the new bubble flow path were larger than those of the conventional venturi channel. By introducing the simulated data into the empirical formula, the calculated particle size of micro-bubbles produced at the exit of traditional venture tube was about 2 times of the new bubble breaking mechanism. The results indicated that the new bubble breaking mechanism can produce smaller microbubbles. In order to improve the bubbling efficiency of axial swirling type microbubble generator, the optimization design of new type bubble breaking mechanism was taken. The structure of the rotating element was optimized by the corresponding surface method. The optimized blade exit angle was 35°, the center cylinder diameter was 12.3 mm, and the leaf length was 10 mm. The particle size of microbubbles produced by the optimized bubble breaking mechanism was calculated to be 75% before optimization, which indicated that the optimized new type bubble breaking mechanism can deeply improve bubbling efficiency of axial swirling type microbubble generator.