Micro Bubble and Sonoluminescence

Abstract

The author reviews the interaction of micro bubbles with ultrasound. First, the action of acoustic radiation pressure on bubbles is discussed in contrast with that on small particles noting the concept of Bjerknes force, resonant bubbles and nonlinear oscillation of bubbles. In the past decade, sonoluminescence, light emission from a single oscillating bubble, attracted attention of researchers because of its strange characteristics. A short history of sonoluminescence and its characteristics are summarized based on bubble motion in a sound field. Lastly, industrial and medical applications of extreme environment generated by collapsing micro bubbles are discussed as promising technology in the new century.

Froth Separation of Ferrihydrite Slurry Using Microbubbles with Ultrasonic Irradiation

“…The primary and secondary Bjerknes forces decrease with increasing ultrasonic frequency, with the secondary Bjerknes force decreasing more than the primary and being approximately inversely proportional to the fourth power of ultrasonic frequency. 12,13,16) At 38 kHz in this study, it was supposed that the primary and secondary Bjerknes forces strongly acting on the microbubbles in the slurry caused the abrupt clustering and raising of the bubbles leaving the colloidal particles in the aqueous medium. Figure 6 shows photo images of microbubble motion in water at a frequency of 38 kHz and an output power of 600 W observed using the high-speed video camera.…”

“…The clusters avoided the pressure antinodes during their rapid rising because clusters sized around 300 mm are larger than the resonant radius at 38 kHz. 12) On the other hand, at a frequency of 430 kHz, the sizes of microbubbles in the experiments were mostly larger than the resonant radius. The microbubbles moved to the pressure node where aggregations are much slow and loose due to weaker secondary Bjerknes forces than that at 38 kHz, enabling the carrying and separation of the ferrihydrite particles.…”

“…The detailed explanations and equations of ''Bjerknes force'' have been shown in literatures. [8][9][10][11][12][13] If there is only a single bubble, it is trapped in the antinode, then oscillated. 17,18) On the other hand, if the bubble is larger than the resonant radius, it moves to a node of sound pressure distribution where the bubble does not strongly oscillate because of the lower amplitude of the sound pressure.…”

“…And, the controlling the motion of microbubbles by the action of the ''Bjerknes force'' on a bubble in an ultrasonic acoustic field was investigated. [8][9][10][11][12][13] A bubble placed in a field with a pressure gradient receives a force, the so called primary Bjerknes force, that is in proportion to its volume and pushes the microbubble from higher pressure to lower pressure. If the bubble is small and oscillates in the ultrasonic standing wave, it moves toward the pressure antinode.…”

“…If two bubbles are oscillating in phase, they attract one another and this force governs the aggregation and clustering of bubbles. 12,13) The aggregated and clustered bubbles caused by the secondary Bjerknes force are rapidly rising by their own buoyancy and the effect of the primary Bjerknes force.…”