抄録
Many types of interesting flows were observed when the water contained in a microspace, such as a microchannel of a few hundred micrometer width and depth, was irradiated by ultrasound at frequency in the range from 20kHz to 1MHz and intensity of several hundred of milliwatts per square centimeter. If a bubble exists in the microchannel, microstreaming of different mode and strength were observed depending on the size of bubble, input power and ultrasonic frequencies. Several hundred of yeast cells, added as tracer, were effectively collected around the oscillating bubble of about 100μm in diameter. When the bubble size was as small as about 10μm, a violent circulating microstreaming was observed around the bubble. In this case, the yeast cells were carried in streaming orbits and the cells might be damaged by the collision and the strong shearing stress at the boundary layer of the bubble. Some interesting types of flows were observed in microchannel even in the case without bubbles. Periodic gathering of yeast cells in the direction of channel was one of the typical flow in a microchannel. On the other hand, yeast cells could be accumulated at the center part of the channel by the circulating flow from the side wall to the center.
