Heat Transfer Characteristics of Acoustic Streaming by Longitudinal Ultrasonic Vibration

摘要

Heat transfer characteristics of acoustic streaming generated by longitudinal ultrasonic vibration at 30 kHz are presented. To investigate the enhancement of heat transfer capability of acoustic streaming, the temperature variations of the heat source and air in the vicinity of the heat source are measured in real time. It is observed that ultrasonic vibration instantly induces acoustic streaming and results in the significant temperature drop as a result of the bulk airflow caused by acoustic streaming. The cooling effect on the heat source is found to have strong correlation with the gap between the ultrasonic vibrator and heat source; the cooling effect is maximized when the gap corresponds to the multiple of half-wavelength of the ultrasonic wave. This result is attributable to the resonance of the sound wave. The theoretical analysis of the dependence of cooling capability of acoustic streaming on the gap is performed as well. Temperature distribution in the gap along the radius and the direction normal to the vibrating surface is measured while acoustic streaming is induced. Variations of temperature drop along the radius are not observed, but temperature drop significantly decreases with the distance from the heat source. The advantage of the cooling method using acoustic streaming is noise free because of the ultrasonic vibration. Moreover, this cooling method can be applied to the micro-electro-mechanical systems, where the fan-based conventional cooling method cannot be employed.