Analysis of an ultrasonic field attenuated by oscillating cavitation bubbles

Abstract

This paper numerically analyzes the sound pressure on an object in an ultrasonic cleaning vessel by considering the dissipation of cavitation bubbles. To clarify the effect of ultrasonic attenuation on the number of cavitation bubbles, the cavitation intensity on a brass object is measured experimentally by changing the quantity of water. Then, the analyzed sound pressure results are compared with the measured cavitation intensity results. The energy dissipation by the oscillation of bubbles is estimated by the irreversible process of heat and mass transfer. The calculation is carried out for the natural oscillation and forced oscillation of cavitation bubbles. It is found that the dissipation of thermal conduction results from the radial oscillation of bubbles by ultrasound. The sound pressure calculated by this dissipation agrees with the cavitation intensity profile estimated using experimental results from the erosion loss of aluminum foil. As the quantity of the water in the cleaning vessel is increased, the sound pressure becomes lower. This is because the amount of energy dissipation of the ultrasonic wave increases proportionally to the number of bubbles. However, when the standing wave causes resonance between the ultrasonic generator and the block, the effect of the sound pressure on the bottom of the block is not disturbed by the water volume.