Abstract:

The application of swirl shear constitutes an essential approach for enhancing the bubble formation performance of the conventional Venturi tube microbubble generator. However, the wake effect will intensify the coalescence of bubbles and significantly impact the ultimate bubble formation quality. Installing the rotation-breaking structure at the Venturi tube outlet proves to be an effective solution to the coalescence issue of the microbubble wake. Nevertheless, the majority of the related research remains at the qualitative description level and lacks quantitative characterization and in-depth analysis. In this paper, we proposed two kinds of new rotation-breaking structures, and Sauter mean diameter and dispersion coefficient of bubble formation were utilized as evaluation indicators to compare and analyze the breaking effect and bubble formation characteristics under diverse structural and operating parameters with the assistance of the high-speed camera and wire-mesh sensor. The experimental results demonstrated that the performance of cross-plate rotation-breaking structure was conspicuously superior to that of the center baffle rotation-breaking structure. Sauter mean diameter was reduced by 4.0% compared to that of the center baffle rotation-breaking structure, and the inlet and outlet pressure drop by 33.7% compared to that of the center baffle rotation-breaking structure. In contrast to the non-installation of the rotation-breaking structure, Sauter mean diameter declines by 12.7%, and the inlet and outlet pressure drop increased marginally by 1.18%. When the plate length increased from to 45mm, the average particle size of the foam-forming Sauter mean diameter decreased from 0.43mm to 0.30mm, and the inlet and outlet pressure drop rises from 165.1kPa to 215.2kPa, with the growth rate decelerating significantly when the plate length exceeded 15mm. From the perspective of the influence of working parameters, the apparent liquid velocity and gas velocity exert a substantial influence on the efficiency and foaming performance of cross-plate rotation-breaking structure microbubble generator. When the apparent liquid velocity escalated from 0.56m/s to 1.70m/s, Sauter mean diameter by the cross-plate rotation-breaking structure decreases by 64.7%. The dispersion coefficient dropped by 81.9%, and the gas phase distribution uniformity increased. The apparent gas velocity increased from 1.33m/s to 3.98m/s, and Sauter mean diameter and dispersion coefficient of the bubble increased, attaining the maximum values of 0.51mm and 1.48, respectively, at 3.98m/s.

Key words: microbubbles, Venturi tube, swirl shear, breaking structure, sauter mean diameter, dispersion coefficient

摘要：

旋流剪切技术的应用是提升常规文丘里管式微气泡发生器成泡性能的重要途径，但其产生的尾流效应将加剧气泡聚并，从而影响最终成泡质量。在文丘里管出口处加装破旋结构是解决微气泡尾流聚并的有效途径，但相关研究多数停留在定性描述层面，缺乏定量表征和深入分析。为此本文提出两种新型破旋结构，借助高速摄像和Wire-mesh金属丝网传感器，以成泡索特平均粒径和分散系数等作为评判指标，对比分析不同结构参数和操作参数下的破旋效果和成泡特性。实验结果表明，安装交叉板式破旋结构时的工作性能明显优于中心挡板式破旋结构，成泡索特平均粒径同比中心挡板式破旋结构下降4.0%，而进出口压降同比下降33.7%；与不安装破旋结构相比，成泡索特平均粒径下降12.7%，进出口压降同比略微增长1.18%。交叉板式破旋结构的板长对成泡效率影响显著，当板长由0增至45mm时，成泡索特平均粒径从0.43mm降至0.30mm，进出口压降由165.1kPa增长至215.2kPa，且当板长超过15mm后增长幅度明显减缓。此外，表观液速和气速对安装交叉板式破旋结构旋流文丘里管式微气泡发生器的破旋效果和成泡性能影响显著，表观液速由0.56m/s增至1.70m/s时，交叉板式破旋结构的成泡索特平均粒径下降64.7%，分散系数下降81.9%，气相分布均匀度提升；表观气速由1.33m/s增至3.98m/s，成泡索特平均粒径和分散系数随之增加，在气速为3.98m/s时分别达到最大值0.51mm和1.48。

关键词: 微气泡, 文丘里管, 旋流剪切, 破旋结构, 成泡索特平均粒径, 分散系数