Exploring the effect of ultrasonic vibrations on the thermohydraulic performance in a minichannel heat sink: Numerical analysis of experimental results

Abstract

Ultrasonic ( US ) applications in thermal systems contribute to the disruption of the boundary layer and the increase of mixing in fluids, thus improving overall system performance. Utilizing this phenomenon, this study aimed to investigate the effect of US power and various heat inputs (Q̇) on the thermohydraulic performance and entropy generation in a rectangular minichannel heatsink. The effect of US on MCHSs has not been comprehensively investigated in the literature, both experimentally and numerically. This study aims to fill this gap and provide a scientific contribution to thermohydraulic performance and entropy generation. For this purpose, a test rig was designed and built. The heatsink was made of copper, and a 27.8 kHz US transducer with P us = 9.9 W input power was applied to the top wall of the heatsink. ANSYS Fluent 2024 R1 was used to solve the governing equations in numerical analysis. The analyses were performed under laminar flow conditions with a range of Reynolds numbers ( Re ). The results obtained from the experiments and numerical simulations demonstrated reasonable agreement, both with each other and with literature correlations. The results showed that the average Nusselt number ( Nu ) increased by 14% when Q̇ was increased from 50 W to 60 W, and by 13% when US was applied. The US application provides a more homogeneous temperature distribution in the channel and header, especially at low Re . It was determined that Q̇ did not affect the friction occurring in the system, but the friction effect of US was more dominant, especially at low Re . Increasing the Q̇ to the system worsened the performance by increasing thermal entropy generation (Ṡgen, thermal) up to 30%. In contrast, the use of US improved the performance by reducing Ṡgen, thermal by up to 4.5%. The situation was reversed for frictional entropy generation (Ṡgen, frictional), where increasing Q̇ yielded a decrease of up to 5%. However, when the US was applied, there was a 38% increase in Ṡgen, frictional at Re = 84 for each Q̇ and Ṡgen, thermal is more dominant than Ṡgen, frictional. In other words, compared with conventional MCHSs without US , the proposed US -assisted system increased the average Nu by 13% and reduced the Ṡgen, thermal by up to 4.5%, resulting in a significant improvement in performance.