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

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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.