Firstly, vertical and horizontal types of liquid atomization equipments were made, using 20 kHz ultrasonic vibration. As the ultrasonic sources some magneto-strictive ferrite transducers were used, attached with a stepped horn and a conical horn made of aluminum, and driven by a 300 Watt type ultrasonic generator (Figs. 1 and 2). According to the results of the atomization efficiency tests on these equipments, their atomization ability was above 20 liters per hour and it was not much affected by the frequency deviation of the ultrasonic oscillator (Figs. 4〜7). Thus it was confirmed that our atomization equipments may be applied to internal combustion engines, oil burners and so on. There have been many sugestions that the cause of the liquid atomization by ultrasonics is due to the unstable surface waves of large amplitude produced on the liquid surface. But there are also some who held the view that cavitation bubbles produced in the liquid partly cause the liquid atomization phenomena. In order to determine the cause of liquid atomization phenomena, a barium titanate transducer was attached to the top of the conical horn. When the test liquid was atomized on its surface, the output waveform of the barium titanate transducer was observed by an oscilloscope and analyzed by a frequency analyzer. Moreover, an aqueous solution of luminol was used as a test liquid and we examined whether the so-called sonoluminescence could be observed or not in the dark field. As a result we were able to confirm that cavitation bubbles were not produced in the liquid in our experimental conditions liquid atomization. Secondly, we attached a test piece, as shown in Fig. 12, to the top of the conical horn. Driving the transducer of the atomization equipment by means of ultrasonic pulse waves, we experimented in order to make the test liquid atomize (Fig. 11). The results obtained confirmed that when the frequencies of the control pulse wave were in the range from 60 Hz to 100 Hz, the efficiency of liquid atomization was much decreased (Fig. 14). In the case when the frequency of the control pulse was equal to 120 Hz, photographs of the surface waves of the liquid in the atomizing state ware taken (Fig. 15). These photographs show the fact that the standing waves were produced in the liquid surface on the ringed part of the test piece and that minute droplets of the liquid were driven off from the top of the waves. We rationalized these experimental results by means of an approximate theory and thus explained the reasons why such stationary, standing waves were produced.
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