Collective bubble dynamics near a surface in a weak acoustic standing wave field

Abstract

The transport of bubbles to a neighboring surface is very important in surface chemistry, bioengineering, and ultrasonic cleaning etc. This paper proposes a multi-bubble transport method by using an acoustic standing wave field and establishes a model which explains the multi-bubble translation by expressing the balance between Bjerknes forces and hydrodynamic forces on a bubble in a liquid medium. An uniform one-dimensional acoustic standing wave field was created by a multi-layered resonator which was designed based on a one-dimensional equivalent network model. A pair of modified Keller-Miksis equation and translation equations, which take into account the influence from boundary surfaces and neighboring bubbles, were used to simulate the bubble translations. The bubble translations were observed by a high speed camera system. Results indicated that the bubble translations were mainly influenced by the acoustic wave field, the boundary, neighboring bubbles, and buoyancy force from the surrounding liquid. The primary Bjerknes force generated by the sound field dominated the bubble translations at the beginning when the bubbles were far away from the boundary. A surge of attractive secondary Bjerknes force from the boundary was seen when the bubbles were approaching the boundary. The attraction force outweighed the primary Bjerknes force within a short distance of the surface and resulted in a faster bubble motion. Besides the forces generated from the acoustic field and the boundary, neighboring bubbles also exerted secondary Bjerknes forces on a target bubble and influenced its translation. Moreover, to optimize the bubble translation in a multi-bubble environment, a parametric study was carried out to investigate the influence of varied bubble size and acoustic pressure amplitudes on the bubble translation. It was found that increasing the size of a bubble can hardly alter its trajectory but only force it to move at a faster speed. An increase of pressure amplitude can also accelerate the bubble motion and enhance the bubble-bubble interaction. The secondary Bjerknes force between two bubbles can switch from an attractive one when they oscillate in phase, to a repulsive one when the bubble oscillations are out of phase. These findings provide an insight into the multi-bubble translation near a surface and can be applied to future bubble motion control studies, especially in drug delivery, sonoporation, and ultrasonic cleaning.

Experimental and theoretical analysis of secondary Bjerknes forces between two bubbles in a standing wave

“…Therefore, existing experimental studies are either qualitative [20,21] or restricted to long bubble-bubble separations (>2 mm) and large bubble sizes in the order of millimeters [4,16]. Recently, trajectory and sign change in secondary Bjerknes force for bubbles with sizes in the micrometer range and with shorter distances have been reported [17,22,23], however, these experiments were conducted with the bubbles near or adhered to a surface. In addition, due to difficulties associated with these experiments, usually one ultrasound frequency and power level alone is studied.…”

Research of the Influence of Low-Frequency and High-Frequency Actions on Processing of Technological Environments

“…Therefore, it is possible to state that there is a problem of finding solutions on a new model of the notion of a process that is adequate to the real. The high-frequency modes of processing include the acoustic method [4]. Cavitation operating modes should significantly differ from the vibration values of the parameter: sound frequencies (f=20-20 10 3 Hz) and ultrasonic -(f=20 10 3 -10 8 Hz).…”

In-phase synchronization between two auto-oscillating bubbles

“…At the heart of these spatiotemporal structures is the mutual interaction between neighboring bubbles. While the interaction of many bubbles has received a great deal of interest [5][6][7][8][9][10][11][12][13][14][15][16][17][18][19], the study of the specific interaction between two oscillating bubbles remains an experimental challenge [5,9,13,[16][17][18]. Besides experimental complexity, a more fundamental problem is that the acoustic interaction of two bubbles is clouded by the external sound field driving the bubbles into oscillations.…”