Abstract We present an experimental study on hydrodynamic cavitation generated by accelerating liquid through a series of constrictions in the presence of gas bubbles and explore its possible applications in water treatment with particular example in aquaculture industry. The formation of intense cavitation bubbles is visualized using a high-speed photography. The cavitation is initiated when a gas bubble moves towards a narrow cylindrical constriction where it accelerates, expands and then splits into smaller bubbles owing to the sharp pressure gradient of the liquid flow inside the constriction section. As the bubbles emerge downstream from the constrictions, they are exposed to a higher pressure region and collapse violently forming a cloud of bubbles. Smaller and more dispersed bubbles are produced by further passing the bubbles through a second series of constrictions. By introducing gas bubbles that serve as cavitation nuclei prior to the constriction, it is unnecessary to force the liquid flow below its vapor pressure to produce intense cavitation, thus enhancing the cavitation activities. We also present experimental evidences of a significant reduction of gram-negative Escherichia coli concentration after exposing them to the cavitation bubbles. Yet, the cavitation bubbles are found to be not sufficiently strong to lyse endospores Bacillus subtilis that are widely used in aquacultures. Graphic abstract

中文翻译：

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气核辅助水动力空化用于水产养殖水处理的实验研究

摘要 我们提出了在气泡存在的情况下通过一系列收缩加速液体产生的水动力空化的实验研究，并以水产养殖业的具体例子探索其在水处理中的可能应用。强烈空化气泡的形成使用高速摄影进行可视化。当气泡向狭窄的圆柱形收缩部分移动时，由于收缩部分内液体流动的急剧压力梯度，气泡在该收缩部分加速、膨胀然后分裂成更小的气泡，从而引发空化。当气泡从收缩处向下游出现时，它们会暴露在更高的压力区域并剧烈崩溃，形成一团气泡。通过进一步使气泡通过第二系列的收缩，产生更小和更分散的气泡。通过在收缩之前引入作为空化核的气泡，没有必要迫使液体流动低于其蒸气压以产生强烈的空化，从而增强了空化活动。我们还提供了在将革兰氏阴性大肠杆菌暴露于空化气泡后显着降低的实验证据。然而，发现空化气泡不足以溶解广泛用于水产养殖的枯草芽孢杆菌内生孢子。图形摘要 没有必要迫使液体流动低于其蒸气压以产生强烈的空化，从而增强了空化活动。我们还提供了在将革兰氏阴性大肠杆菌暴露于空化气泡后显着降低的实验证据。然而，发现空化气泡不足以溶解广泛用于水产养殖的枯草芽孢杆菌内生孢子。图形摘要 没有必要迫使液体流动低于其蒸气压以产生强烈的空化，从而增强了空化活动。我们还提供了在将革兰氏阴性大肠杆菌暴露于空化气泡后显着降低的实验证据。然而，发现空化气泡不足以溶解广泛用于水产养殖的枯草芽孢杆菌内生孢子。图形摘要