| Summary: | 碩士 === 國立成功大學 === 機械工程學系碩博士班 === 96 === Now, there are many methods which can produce nano-powder. Using high intensity ultrasound is one way of those methods. The ultrasound is generated using a piezoelectric transducer and is amplified thru a horn emersed in liquid. Enormous cavitation bubbles are then produced around the horn tip and cause the effects of materials refined and sonochemistry. But this method will make the horn tip be quickly eroded by cavitation bubbles. The erosion not only shortens the life time of the horn, but also pollutes the sample in sonochemical cell.
In this study, we design a sonochemical cell so that the problem of the horn tip erosion can be avoided. First, we use the software COMSOL to simulate the acoustic field in the cell. The idea is to find a resonant acoustic mode in which the largest acoustic pressure is moved from the horn tip to the inside of the cell. The size of the cell must be designed so that the resonant frequency corresponding the mode matches that of the piezoelectric transducer. Once the resonant mode is achieved, very large normalized acoustic pressure can be obtained away from the horn tip. So we design a cell which the resonance properties and the acoustic pressure field modal accord with the demands.
Experimentally, we use hydrophones to measure the acoustic field in the cell and confirm the results of the simulation. A novel horn with enlarged cross-sectional area is proposed and used to excite the resonant acoustic mode. It is shown that this method can generate cavitation bubble field at a location inside the cell accord with the demands. That is, we can avoid tip erosion by cavitation bubbles also prove that the cell has a big effect to acoustic pressure field.
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