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液态涡流场不仅可以传质传热, 影响声场分布, 还可以影响流场中气泡的行为特性, 进一步影响声空化效果. 以三维漏斗形涡流场中气泡的动力学方程并结合气泡破碎理论为基础, 研究了涡流场(搅拌产生的流场)对气泡破碎概率及其气泡空化效果的影响. 结果表明, 随着转速的增大, 气泡的破碎概率显著提高, 同时气泡破碎临界半径逐渐减小, 从600 rad/min时的200 μm降至2000 rad/min时的55.5 μm, 这意味着在高速旋转的涡流场中, 气泡在尚未膨胀到应达到的最大空化半径时就提前发生破碎, 导致其失去空化效应, 从而降低超声降解效果. 实验结果进一步验证了声空化效果在适中转速(600—1000 rad/min)下最佳, 而过高转速则会抑制降解效果. 这些发现为声空化技术的优化提供了理论基础和实验支持.
The liquid vortex flow field plays a crucial role not only in the transfer of matter and heat but also in significantly affecting the distribution of sound fields, which in turn influences the behavior of bubbles in the flow. This ultimately affects the phenomenon of acoustic cavitation. Based on the combination of the theory of bubble fragmentation and the theory of funnel-shaped vortex, in a three-dimensional vortex field. The effect of the vortex flow field (flow field generated by stirring) on the bubble breakup probability, as well as its modulation of acoustic cavitation, is investigated in this paper. In addition, the phenomena observed in experiments are explained. When the stirring speed reaches 1000 rad/min, the degradation effect no longer shows a monotonic increase, but instead begins to decline. It is demonstrated that with the increase of stirring speed, the probability of bubble breakup increases significantly. For instance, when the stirring speed is 1000 rad/min, the probability of bubble breakup is about 0.17%. At a stirring speed of 1500 rad/min, the breakup probability rises to 23%, and at 2000 rad/min, it reaches 44%. Moreover, the critical radius for bubble breakup decreases. The critical radius, as defined in this study, refers to the bubble radius at which the probability of breakup becomes nonzero. Experimental data show that at 600 rad/min, the critical radius for bubble breakup is about 200 μm, while at 2000 rad/min, it shortens to 55.5 μm. This indicates that in a high-speed rotating vortex field, bubbles may rupture before reaching their maximum cavitation radius, thus losing their effective cavitation effect. Further analysis shows that in the vortex flow field, for bubbles with an initial radius smaller than 22.5 μm, the temperature inside the bubbles upon collapse can reach as high as 2217.3 K (corresponding to an initial radius of 22.5 μm). For bubbles with an initial radius of 20 μm, the collapse temperature can even reach 2264.3 K. For bubbles with an initial radius of 40 μm, when the stirring speed does not exceed 1500 rad/min, the bubbles can still collapse under the action of the sound field, and the temperature inside the bubble upon collapse can reach 1659.6 K, which is sufficient to trigger off the cavitation effect. However, when the stirring speed exceeds 1500 rad/min, bubbles may break up too quickly and lose their cavitation capacity, thus failing to produce the expected cavitation effect. Experimental results further verify that at moderate stirring speeds (600—1000 rad/min), the acoustic cavitation effect is most pronounced, while excessively high stirring speeds suppress the enhancement of the degradation effect. This phenomenon suggests that the introduction of the vortex flow field makes the factors affecting acoustic cavitation more complex. The optimization of the acoustic cavitation effect requires not only the consideration of the sound field distribution and mass transfer but also the comprehensive factors such as gas entrainment, bubble aggregation, and breakup. Therefore, a thorough analysis and regulation of these factors are crucial for the widespread application of acoustic cavitation technology in engineering, with important theoretical value and practical significance, providing scientific basis and direction for further optimizing the acoustic cavitation process. -
Keywords:
- acoustic degradation /
- vortex field /
- bubble breakage /
- acoustic cavitation
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图 1 理论涡流场中质点运动粒子轨迹图
Fig. 1. Trajectory diagram of particle motion in a theoretical vortex field.
图 2 不同转速下, 气泡破碎概率随气泡半径变化曲线
Fig. 2. Bubble fragmentation probability as a function of bubble radius at different rotation speeds.
图 3 气泡初始半径破碎概率随转速的变化
Fig. 3. Variation of bubble fragmentation probability with rotation speed for different initial bubble radii.
图 4 涡流场中声空化泡的破碎特性 (a) 1500 rad/min, 2000 rad/min转速下不同初始半径气泡破碎示意图; (b) 1000 rad/min, 1100 rad/min转速下不同初始半径气泡破碎示意图; (c) 1500 rad/min, 2000 rad/min转速下不同初始半径气泡破碎温度示意图; (d) 1000 rad/min, 1100 rad/min转速下不同初始半径气泡破碎温度示意图
Fig. 4. Fragmentation characteristics of cavitation bubbles in a turbulent flow field: (a) Schematic diagram of bubble fragmentation with different initial radii at 1500 rad/min and 2000 rad/min speeds; (b) schematic diagram of bubble fragmentation with different initial radii at speeds of 1000 rad/min and 1100 rad/min; (c) schematic diagram of bubble fragmentation temperature at different initial radii at 1500 rad/min and 2000 rad/min speeds; (d) schematic diagram of bubble fragmentation temperature at different initial radii at speeds of 1000 rad/min and 1100 rad/min.
图 5 涡流场中声空化对亚甲基蓝降解效果
Fig. 5. Effect of cavitation in a turbulent flow field on the degradation of methylene blue.
表 1 不同搅拌转速对应的气泡破碎半径
Table 1. Bubble fragmentation radius corresponding to different stirring speeds.
搅拌转速/
(rad·min–1)破碎半径/μm 搅拌转速/
(rad·min–1)破碎半径/μm 500 251.1 1200 90.6 600 200.2 1300 85.4 700 175.1 1400 82.5 800 159.3 1500 78.0 900 136.6 1600 71.5 1000 122.1 1800 62.4 1100 99.5 2000 55.5 
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