The Influence of Ultrasonic Vibrations on Convective Heat Transfer and Pressure Dynamics in Multi-Geometrical Heat Transfer Systems Using Water, Propylene Glycol, and Ionic Liquids

Abstract

Thermal management in modern devices has become increasingly challenging due to the higher heat output from advanced electronics. Effective cooling solutions are essential to enhance performance, extend operational life, and reduce device failure rates. For every 10℃ increase in ambient temperature, device lifespan decreases by 50%, underscoring the need for innovative cooling methods. Micro/minichannel heat sinks have emerged as a promising solution due to their compact size and low thermal resistance. Various mechanisms have been studied to enhance thermal performance, including novel geometries, tailored fluid properties, and the use of ultrasonic waves. Ultrasonic waves have gained attention for their potential to improve heat transfer by disrupting boundary layers and enhancing fluid mixing. This thesis explores whether ultrasound can enhance thermal system performance and investigates the influence of key fluid properties, material selection, and varying parameters such as flow rate, heat input, and ultrasound power on heat transfer and pressure drop. Three experiments were conducted to evaluate the effects of ultrasonic vibrations on heat transfer and pressure drop across different systems. In the first experiment, ultrasonic vibrations enhanced heat transfer by 13.5% in a circular minichannel heat sink made of stainless steel, using water as the coolant. In the second experiment, using a rectangular minichannel heat sink with water and propylene glycol-water mixtures, ultrasound improved heat transfer, with the highest enhancement observed in deionized water, while the effectiveness decreased with higher propylene glycol concentrations. The third experiment, conducted in a horizontal copper tube, showed a 13.5% heat transfer improvement for water and 11.3% for an ionic liquid. Across all experiments, the effect of ultrasound diminished as flow rates increased, and higher viscosity fluids reduced its effectiveness. Additionally, ultrasound contributed to an increase in pressure drop in all cases. Overall, these findings highlight the potential of ultrasonic vibrations as an effective technique for enhancing heat transfer. This thesis could provide a basis for future research into ultrasonic technology as a promising technique.