INVESTIGATION OF HYSTERESIS IN ACOUSTICALLY DRIVEN CHANNEL FLOW AT ULTRASONIC FREQUENCY

ABSTRACT

The purpose of this article is to investigate the hysteresis phenomenon in the acoustic streaming flow in a channel. The channel is bounded by one stationary beam and one beam vibrating in a standing wave form. According to Wan and Kuznetsov [1-2], the acoustic streaming within the channel is driven by the slip velocity at the edge of the acoustic boundary layer near the vibrating beam. The streaming flow exhibits two different types of flow patterns at small and large channel widths. In this article, a transition between these two flow patterns and the corresponding jump in the Nusselt number as the channel width changes is investigated. As a result of extensive numerical investigations, a hysteretic region is discovered. When the channel width falls into the hysteresis region, the flow pattern and the heat transfer efficiency depends on whether the channel width is increasing or decreasing. Outside the hysteresis region, such dependence does not exist.

Acknowledgments

The authors are grateful to Prof. W. L. Roberts of North Carolina State University for drawing their attention to the present problem. The authors also acknowledge with gratitude National Science Foundation Grant ECS-000026. Helpful comments from Drs. P. I. Ro and A. I. Kingon are greatly appreciated.