EXPERIMENTAL INVESTIGATION OF THE EFFECT OF ULTRASONIC INLET FLOW ON HEAT TRANSFER INSIDE THE HORIZONTAL MINI-TUBES by Ip Chi Wai Thesis Supervisor: Prof. Lap Mou Tam Master of Science in Electromechanical Engineering Ultrasound has been widely used in the drying, welding, cleaning, chemical, and heat transfer processes. Moreover, in recent years there has been an increased interest in the application of ultrasound for heat transfer enhancement in the field of heat transfer. However, a few papers investigated the effect of ultrasound on heat transfer inside the horizontal tube, especially, the smaller diameter tube. Therefore, the objective of this experimental study is to investigate the influence of ultrasound on the heat transfer inside the horizontal mini-tubes under the uniform wall heat flux boundary condition. In this study, the stainless steel test tubes with the inner diameter of 1.3 mm and 2 mm were used as the test section. The entrance and fully developed regions heat transfer coefficients were analyzed. The Reynolds number ranged from 1000 to 3000. A series of experiments with the different ultrasonic powers were conducted. The results showed that the heat transfer enhancement by ultrasound was observed in the 2 mm and 1.3mm tubes. Moreover, the heat transfer was increased by the increase of ultrasonic power.