Acta Physica Sinica, Volume. 68, Issue 23, 234302-1(2019)

Influence of large bubbles on cavitation effect of small bubbles in cavitation multi-bubbles

Qinghim and Naranmandula *

In previous papers, researchers generally adopted a simplified assumption that there is a single type of bubble in liquid. In this paper, two simplified bubbles models are established based on the shape and structure of cavitation bubbles formed in ultrasonic field, i.e. linear model consisting of three bubbles and cluster model composed of five bubbles, and each model is assumed to consist of two types of bubbles. The influences of large bubbles on cavitation effect of small bubble in the middle for three- and five-bubble model are numerically studied by using the modified Keller-Miksis equation and van der Waals equation. The changes of the expansion radius of the small bubble in the middle, the temperature in the small bubble and the secondary Bjerknes force between large bubble and small bubble with the increase of the initial radius of large bubbles are mainly investigated. In the calculation, it is assumed that the locations of bubbles stay unchanged and the shape of bubbles remains spherical in the oscillation process. Meanwhile, the time-delay effect on the secondary Bjerknes force can be neglected because the sound wave speed is very fast in water and the bubbles in the liquid can oscillate synchronously. The calculation results show that the expansion of small bubble in the middle can be completely suppressed or delayed when the initial radius and the number of bubbles are appropriate on condition that the distance between large and small bubble, the driving sound pressure and frequency of the applied sound field stay unchanged. The main reason for delayed expansion is that the total pressure acting on small bubbles is delayed to form a negative pressure in the process of the change. The collapse time of delayed expansion of small bubble is basically the same as that of large bubbles, which makes small bubble collapsed rapidly and thoroughly under the strong radiative barotropic effect of large bubble's collapse, and leads the maximum temperature in the small bubble to be higher than that of the single bubble with the same initial radius and the small bubble with normal expansion. In addition, when the expansion of small bubble is delayed, the secondary Bjerknes force between the large bubble and the small bubble appears to be repulsive first and attractive then. This rule is different from the change rule of the secondary Bjerknes force between the two bubbles in normal expansion. The results in this paper have significant theoretical guidance for specific problems such as suppressing liquid cavitation or enhancing liquid cavitation effect by the manual injection of large bubbles.

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Qinghim , Naranmandula . Influence of large bubbles on cavitation effect of small bubbles in cavitation multi-bubbles[J]. Acta Physica Sinica, 2019, 68(23): 234302-1

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Paper Information

Received: Aug. 5, 2019

Accepted: --

Published Online: Sep. 17, 2020

The Author Email:

DOI:10.7498/aps.68.20191198

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