Experimental Study of Boiling Heat Transfer in the Applied Field of Fluid Vibration

研究了超声波对沸腾换热的影响。在直径为0.20 mm的细加热器上进行了一系列的换热实验。水平铂丝，浸泡在饱和的乙醇醇中，暴露在28 kHz的超声波下。对较高热流密度的核态沸腾换热和最大热流点影响不大。膜沸腾换热系数则随着铁氧体振子功率的增加而增加，在本实验条件下，膜沸腾换热系数增加一倍，达到最大值。最小热流点也得到了改善。当过热度低于MHF线时，晶核沸腾和膜沸腾沿焊丝分别并存。研究了超声波强度与膜沸腾换热强化效果之间的相互关系，用带有压电式传感器的超声波探头测得的强度分布类似于半波长的正弦波。在光强最大的位置获得了最大的增强率，并证明了它们之间有很强的相关性。然而，实验结果也表明，除了超声波强度本身外，还存在另一个强化膜沸腾换热的原因。

The effect of ultrasonic wave application on boiling heat transfer is investigated. A series of heat transfer experiments are carried out using a fine heater of a 0.20mm-dia. horizontal platinum wire, which is immersed in saturated ethylalxohol and exposed to a 28kHz ultrasonic wave. Little effect is obtained forrelatively high-heat-flux nucleate boiling heat transfer and the maximum heat flux point. The heat transfer coefficient of film boiling, on the contrary, increases with the increase of the power supplied to a ferrite type vibrator and it is doubled for the maximum in this experimental condition. The minimum heat flux point is also improved. At a lower superheat than the MHF line, nucleate boiling and film boiling coexist separately along the wire. Under a high power of the input, many bubbles begin to generate.Interrelation between the ultrasonic wave intensity and the augmentation effect of film boiling heat transfer is studied.The intensity profile, which is measured by a ultrasonic wave probe with a piezo-type sensor, is proved to be like a sine wave function with half wave length of the ultrasonic wave. The maximum augmentation ratio is obtained at the position of the maximum intensity and a strong interrelation between them is proved. However, the experimental results also show that another cause to augment film boiling heat transfer will exist in addition to the ultrasonic wave intensity itself.