| Budget Amount *help |
¥3,400,000 (Direct Cost: ¥3,400,000)
Fiscal Year 1998: ¥900,000 (Direct Cost: ¥900,000)
Fiscal Year 1997: ¥2,500,000 (Direct Cost: ¥2,500,000)
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| Research Abstract |
Agglomeration of particles exposed to sound waves was studied experimentally and theoretically in the present work. The mechanism of acoustic agglomeration is discussed with an emphasis on the particle collision and adhesion. Experiments were carried out under room and high (1300℃) temperatures. In the room temperature experiments, large (Fe, size 75〜90 μm) and fine Mo (averaged diameter 7.26 μm) or FeィイD22ィエD2OィイD23ィエD2 (averaged diameter 14.29 μm) particles were electrically precharged by passing them through a positive (fine particles) and a negative (large particles) corona charger. The charged particles were injected into a vessel within which a standing sound wave was formed and, then, were deposited on a slide. The particle size distribution was analyzed by an optical microscope. In the high temperature experiments, an Ar-OィイD22ィエD2 mixture was blown on to an iron bath (carbon content about 4.2%) melted in a resistance furnace. Simultaneously, a sound wave was propagated to the
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bath surface through the gas phase. Dust emitted during the decarburization reaction was trapped by a quartz or a Mo plate, after which the dust samples were analyzed by a SEM. The sound waves were irradiated by using a set of loudspeakers (1, 3 or 6 units) or a piezocristall generator. The frequency was ranged from 120 to 20776 Hz. Maximal input electrical power was 70 W (set of 6 speakers) and 100 W (piezocristall generator).
The results can be summarized as follows. It was found that the particles are agglomerated with each other even neither acoustic nor electric fields applied. Sound waves of low frequency (120〜270 Hz) caused the particle agglomerates to disintegrate (Fe-Mo system). On the other hand, when the particles were exposed to sound on frequencies more than 300 Hz, the particle agglomeration was enhanced. The higher were the sound frequency and intensity, the larger was the effect of acoustic agglomeration. On the whole, charging of the particles resulted in a better agglomeration efficiency as compared with non-charged particles, especially for the Fe-Mo particle system. The results of the high temperature experiments showed the same tendency for an increase in agglomeration efficiency with sound frequency.
In analyzing the experimental results, two theoretical considerations were used. The first one is the orthokinetic theory supplemented by a developed model of particle collision which makes possible explaining the particle behavior at low and medium frequencies. The second one is the radiation pressure model which provides a reasonable explanation on the sound effect at high frequencies. The presence of unlike electrical charges on the particle surface enhance attraction force between them. This effect is assumed to be of prime importance when the particles approach to each other to such a short distance that the other forces (inertial and radiation forces) become very small. Less
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