Heat Transfer Enhancement Using Ultrasonic Waves in Presence of Liquid: A Basic Research for Cooling Electronic

Abstract

This work collects the experimental results obtained in the Thermal Fluid Dynamics Lab at the Department of Energy, Systems, Land and Constructions Engineering at the University of Pisa, concerning a basic physics research on the influence of ultrasounds in single phase free convection and in subcooled boiling, at atmospheric pressure. The ultrasounds are applied at the set frequency of 40 kHz, with a transducer output changing from 300 to 500W, on a circular horizontal cylinder heated by Joule effect, immersed in distilled water. The tests in single phase free convection, without ultrasonic waves, are validated by means of the classical correlations reported in literature, but they do not produce distinctive augmentation of the heat transfer. The enhancement of the heat transfer coefficient is maximum in subcooled boiling conditions (about 57%). In this regime a detailed investigation was performed to optimize the variables involved, such as the ultrasound generator power, the position of the cylinder and, especially, the subcooling degree. This paper, makes clear systematically the effects of ultrasounds on the heat transfer and shows as they could be very useful as cooling system for the last generation electronic components.