加圧時におけるキャビテーション***ージョン : 加圧時のキャビテーション作用の研究(第2部)

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In this report, we took notice of the erosion effects of an ultrasonic cavitation produced in the gap between parallel planes, i. e. between the test piece and the acoustic irradiation surface of step horn, and examined the effects of the distance of the planes and the static pressure. Cavitation effects are affected by the excitation mode of an ultrasonic transducer, i. e. ultrasonic burst pulse excitation mode and continuous one. Therefore, in this report the experimental results using the ultrasonic burst pulse are also shown. Ferrite transducers (28 kHz) were attached to a 1/2 wavelength-resonant step horn of stainless steel, and excited by an oscillator or a function generator and a 500-watts-type broad band power amplifier. As a test piece of this experiment we used a circular plate of aluminum, whose thickness is 1 mm and diameter is 30 mm. Temperature of this experiment was held at 15±1℃ by a cooling coil that was set in the pressure vessel. Using the continuous irradiation of ultrasound, we held first the hap between the test piece and the horn tip to be constant, and examined the change of erosion weight loss under elevated pressure (Fig. 3). If the gap is from 0. 44 mm to 2. 63 mm, the erosion weight loss has a sharp maximum at an elevated pressure of several atmospheres. If the gap is above 4. 38 mm, the weight loss has also some maximum, but its value is not so large. In case the gap was kept constant at 0. 44 mm, we examined how the peak values of erosion weight loss change with the ultrasonic irradiation time (Fig. 4), and ascertained that the peak values appear under pressure of several atmospheres regardless of the irradiation time. There are few reports on the cavitation erosion under elevated pressure. Sirotyuk, using a 560 kHz transducer, and Angona, using a 30 kHz transducer, examined the erosion weight loss of some test pieces set in an acoustic focal region, and showed that the erosion weight loss has its maximum at some elevated pressure. Our results are similar to theirs in spite of different experimental conditions. Experiment on the cavitation erosion using some ultrasonic burst pulses was only made by Plesset, who showed that he could get more erosion weight loss than by the continuous radiation method under some conditions. Using a function generator and a broad band power amplifier, we obtained arbitrary ultrasonic burst pulses. The gap between the test piece and the irradiated surface of the horn was held 0. 44 mm wide. In this experiment we adjusted the irradiation time so as to the net irradiation time to be constant. When the irradiation time is kept constant at 5 minutes, the erosion weight loss of the test piece gets its maximum under pressure of several atmospheres, and by elevating the static pressure the weight loss gradually decreases to zero (Fig. 7). When we use the ultrasonic burst pulse irradiation, the erosion weight loss is nearly the same as in the continuous one under low pressure, but becomes larger than the continuous irradiation under high pressures. In case the rest time and elevated pressure are constant of 20 msec and 4 kg/cm^2, respectively, changing the time of burst pulse we made an experiment of the erosion weight loss (Fig. 8). We have got the results that the erosion weight loss gets its maximum when the ratio of burst time and rest time of the pulse is 1/2, and by decreasing the ratio, the erosion weight loss diminishes rapidly, and by increasing the ratio, it approaches to a half of its maximum value.
社団法人日本音響学会の論文
1976-06-01

加圧時におけるキャビテーション***ージョン : 加圧時のキャビテーション作用の研究(第2部)

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