This study is concerned with enhancing the heat transfer rate in a falling film layer of ethylene glycol on an inclined rectangular tray by applying ultrasonic waves irradiated from the bottom of the tray. The heat transfer coefficient in a falling film layer of ethylene glycol was determined by the measured temperature distributions under various conditions of liquid flow rate, power supplied to an ultrasonic vibrator and frequency of the ultrasonic wave. The evaporation rate of water from a failing film of ethylene glycol/water mixture was also measured.
As a result, the enhancing effect of ultrasonic irradiation on the heat transfer coefficient was obtained with increasing liquid flow rate. It was found that ultrasonic irradiation of 23.6 kHz was more effective to enhance the heat transfer rate in a falling film layer than 46.9 kHz ultrasonic waves. The heat transfer coefficient in a falling film layer was increased by ultrasonic irradiation in the order about 30%, which was obtained at a film Reynolds number of 50.0 by using 23.6 kHz ultrasonic waves. It was recognized that ultrasonic waves increased the evaporation rate of water in a falling film of ethylene glycol/water mixture.