Augmentation of Natural Convection of Water around a Vertically Heating Cylinder using Ultrasound

Abstract

This research investigated the ultrasonic effects on natural convection of a vertical cylinder in distilled water from 40, 80, 120 kHz ultrasound, having the power of 60 w. The experiment was carried out on a constant heat flux surface at 14,150 Wm^-2 in the test section of 20 cm width x 20 cm length x 20 cm height. The ultrasonic transducer was installed on the side wall of the test section. The distances between the transducer and heating surface were varied as 5, 10 and 15 cm to study the effect of varying ultrasonic frequencies and distances between ultrasonic transducer and heating surface on heat transfer enhancement ratio. The results show that ultrasound can increase the heat transfer enhancement ratio mostly up to 399% under the 40 kHz waves at the distance of 5 cm. The heat transfer enhancement ratio decreases with the increase of the distance.
In addition, an accurately predictive formula for the heat transfer enhancement ratio under 40–120 kHz is also proposed in this paper. Therefore, the obtained experimental results will be important information in order to develop the higher efficiency heat exchangers in the future.