大规模液体中的强超声传播和空化效应

The most of the application of acoustic cavitation effects is usually limited in laboratory scale, and rarely extended to the industrial processes. To form a large-scale intense cavitation field, we need to understand the propagation of the strong ultrasound in gassy liquid, and to optimize and strengthen the cavitation effects in a large volume of liquid. In theory, the bubble dynamics in multi-bubble surrounding will be proposed by using the mean-field approach at first. Since the two-phase fluid dynamics for the gas-liquid mixture is only suitable for the liquid containing small-pulsed bubbles, we will describe the role of the strong-pulsed cavitation cloud by a source function of the wave equation. The source function and its dependence on the local pressure will be obtained by both experiment and theory. Finally we will propose a theoretical model for the acoustic propagation in the cavitating liquid. The numerical investigation based on the model will be carried out and be helpful to form the large-scale cavitation field in experiment. In experiment, at first we will observe and measure the interaction between bubbles to understand the multi-bubble dynamics. As a key investigation of the project we will study the influence of the large-scale cavitation effects on the parameters, such as the shape of the reactor, the structure, the number and the positions of the transducers, and the ultrasound frequency, amplitude and waveform, etc. Combining with the numerical results, we will optimize the parameters and realize the strong cavitation field in a large volume of liquid. The ultrasound-assisted extraction of plant in the cubic-meter scale will be carried out to test the feasibility in industrialization application.

声空化效应多停留在实验室规模，难以进入产业化应用。建立一个大规模、高密度、脉动剧烈的声空化场需要解决含气液体中的强超声传播问题，和大范围声空化效应的优化问题。理论上，我们首先拟采用平均场方法建立气泡云环境中的单气泡动力学模型。然后，考虑到含气泡液体的二相流体理论，只适用小幅脉动的空化场中的声传播问题，拟在声波方程中引入一个源函数来表征空化泡的群体作用。通过实验测量和理论建模获得这个源函数及其与局域声压等的关系，最终给出伴随声空化的声传播理论。完成数值研究，为建立大规模声空化场提供理论指导。实验上，首先，观察气泡间的相互作用，了解多气泡脉动的动力学行为。然后，研究大范围声空化效应与各种参数的关系，比如，反应器形状、换能器结构、个数和空间分布，还有频率、幅度和波形等。结合数值结果，在空化泡产额和脉动强度之间进行优化，建立大规模的空化场。并以萃取植物精油为例，检验大规模应用的可行性。

声空化泡内部具有极端高温高压，声空化效应可以应用于清洗、粉碎、灭活、细胞穿孔、化学和医学等领域。但由于存在空化屏蔽，目前声空化效应多数停留在实验室规模，难以进入产业化应用。本课题通过研究强超声在含气液体中的传播规律，探索扩大声空化范围的有效途径，期望实现声空化效应的产业化应用。通过研究，（1）了解了含气液体中的强超声传播规律，发现空化屏蔽效应引起的反常声传播现象、空化引起的声能量传播的不对称性，以及空化液体中的声禁带现象；（2）发展了基于晶格模型的空化云中的气泡动力学模型，数值计算表明，等声压驱动下，云中空化泡的脉动和单空化泡情形差异并不大，导致空化云中的实际声压显著下降的事实的实验发现；（3）提出了内聚声波、分层液体和温度梯度等3种改善声空化均匀性的方案，并建立了半米尺度的均匀声空化场，可以在超声萃取等产业使用。