| Summary: | 碩士 === 國立成功大學 === 機械工程學系碩博士班 === 97 === Sonochemical effects of high intensity ultrasound come mainly from acoustic cavitation. Cavitation bubble collapse in liquid is so violent that very high local pressure and temperature, combined with extraordinarily cooling, provide a unique environment for driving chemical reactions under extreme conditions. In general, high power ultrasonic sonochemical systems utilize a metal horn to amplify the intensity of the ultrasound generated from a piezoelectric transducer. As a result, cavitation bubbles form near the horn tip, causing severe erosion of the horn, contamination of the sample, and degeneration of the system resonance.
In the study, the COMSOL finite element software is used first to construct a tool for designing and analyzing the ultrasonic sonochemical system. Different physical modules, namely piezoelectric module, structural module, and acoustic module, are coupled together. In order to eliminate the cavitation erosion, an enlarged horn is designed for reducing the energy density of the ultrasound transmitted to the sonochemical cell. Numerical results show that an ideal resonant mode can be found by adjusting the immersed depth of the horn and the radius of the sonochemical cell so that the greatest amplitude of the acoustic pressure is located away from the horn tip. Experimentally, it is confirmed that the various resonant modes observed in the numerical analysis indeed exist. The most important finding of the present study is that focused cavitation field can be generated away from the horn by careful design of the components of the resonant sonochemical system.
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