Abstract

A Life of Sonoluminescing Bubbles

K.Yasui (National Institute of Advanced Industrial Science and Technology, Moriyama-ku Nagoya, Japan)

e-mail: k.yasui@aist.go.jp

Computer simulations of bubble oscillations are performed under conditions of multibubble sonoluminescence(MBSL) in water in order to study a life of bubbles. Bubbles are classified into five categories by their ambient radii. They are dissolving bubbles, stable sonoluminescing bubbles, unstable sonoluminescing bubbles, unstable bubbles, and "degas" bubbles. The range of the ambient radius for each category depends on the frequency and amplitude of ultrasound. A bubble emits light immediately after its appearance when the ambient radius is in a certain range, while the previous theory predicts that a bubble emits light only when it grows to the resonance size by rectified diffusion. The main mechanism of the bubble growth to a "degas" bubble is not the rectified diffusion but coalescence. The mechanism of the light emission depends on the frequency of ultrasound. As the frequency of ultrasound increases, the amount of water vapor trapped inside bubbles at the collapse decreases. As a result, MBSL originates mainly in plasma emissions at 1 MHz while it originates in chemiluminescence of OH radicals and plasma emissions at 20 kHz.

Section : 4