超音波洗浄機などにおける液中全音響パワーの熱量法的測定の実際的仕方
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概要
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Acoustic wave energy once radiated into a bulk of fluid contained in a tank, is finally converted into heat gained by the fluid, with conversion efficiency nearly 100%, after traveling throughout the bulk by undergoing successive perfect reflection at its boundary. It would therefore be possible to determine calorimetrically the total acoustic power existing in the fluid by a simple measurement of the time rate of heat generation (i. e. the rate of temperature-rise) within the fluid. Although the accuracy of this determination procedure was proved to be good in many physical laboratories, the method has never been applied extensively to practical ultrasonic equipment such as cleaning tank. The reason for this appears to lie in that some fundamental precautions are called for from the standpoint of physical experiment on heat, in order to carry out accurate experimentation. The present paper describes the essential precautions needed in the calorimetric determination of acoustic power and also shows that correct results were actually obtained with these precautions on experimenting on some practical cleaning tanks. Fig. 1 shows our simple and general arrangement for the measurement. One ordinary glass-rod thermometer together with a metal gauze protection against strong sonic field is the only essential measuring tool, because the bath becomes equitemperature owing to the natural agitation caused by ultrasonic streaming. Minimization of evaporation heat loss is also necessary to carry out accurate experiment and this problem was ingeniously solved by covering the water surface by a floating sheet of paper heavily wetted with machine oil. The present method gives the accurate total acoustic power, so far as heat generation within the transducers themselves is negligible. Fig. 2(A) and 2(B) show the results of the experiments we carried out on Tank A transducerized with 3 bariumtitanate vibrators and on Tank B with 6 vibrators, giving the measured total acoustic powers of 43. 4W and 97W respectively. These values are in good agreement with the measured electrical input powers. Fig. 3 shows another experiment on Tank A with a bare-wire low-voltage electric heater introduced therein. The difference between the two slopes obtained with and with out the heater power is again in agreement with the heater power itself within experimental error. The present method requires only one ordinary glass-rod thermometer as the essential measuring tool and no modification in the ultrasonic equipment, nevertheless its reliability is excellent and it promises to be a very practical means to determine the total acoustic power within the fluid.
- 社団法人日本音響学会の論文
- 1969-07-20