NUMERICAL INVESTIGATION OF FRACTAL-SHAPED MICROCHANNEL HEAT SINK (MCHS)

Abstract

The problem of effective temperature management has emerged as a significant obstacle to future developments in microelectromechanical systems (MEMS) and high-performance computing devices due to the growing integration and miniaturisation of electronic systems. Because of its small size and high surface-area- to-volume ratio, microchannel heat sinks (MCHS) have become a state-of-the-art option for efficient heat dissipation in constrained locations. This thorough analysis compiles a large body of research on enhancing heat transfer in MCHS using sophisticated geometrical adjustments, nanofluids, and best optimisation strategies. With a focus on passive solutions like geometrical alterations, a first comprehensive analysis offers a thorough overview of state-of-the-art cooling strategies and divides MCHS enhancing techniques into active and passive categories. The study demonstrates how boundary layer development degrades thermal performance in straight channels and how fractal-shaped designs, which naturally produce chaotic advection and secondary flows, provide a ground-breaking method of improving convective heat transfer with negligible pressure drop penalties. Inspired by natural mass and energy transport phenomena, fractal MCHS (FMCHS) designs show exceptional ability to reduce temperature non-uniformity and thermal resistance. In the beginning of the study, simplified MCHS geometries were investigated by adding square ribs with double-filleted and rounded corners. To comprehend the function of local geometric smoothening in flow behaviour and thermal augmentation, three configurations, such as MC-SQ, MC-SQ-FR, and MC-SQ-DFR were examined. Through boundary layer re-development and improved mixing, the results showed that adding fillets to the rib corners significantly improved thermal performance. The MC-SQ-FR design increased Nusselt numbers by 15-22% while only increasing pressure drop by 2-10%. Building on this, a new FMCHS with cavities and ribs was suggested and subjected to ANSYS Fluent numerical analysis. Although there was a corresponding rise in pressure drop, the FMCHS with ribs (FMCHS-R) and diagonally positioned ribs (FMCHS-DR) layouts demonstrated the most notable heat transfer gains among the different configurations examined. An intelligent optimisation framework utilising Artificial Neural Networks (ANN) in conjunction with the Moth Flame Optimisation (MFO) algorithm was utilised to address the design trade-offs. This led vi to an ideal configuration where the best thermal-hydraulic performance was obtained with a rib radius of 26% along the FMCHS paths at a flow rate of 200 ml/min. RSM and HHO optimisation methods were also employed for the fractal microchannel heat sink (FMCHS) with ribs and cavities and show a thermal performance-thermal efficiency trade-off. RSM chose an FMCHS design with ribs (model value 1) and a moderate flow rate of 295 ml/min. The thermal resistance was 0.983, pumping work was 201.112 mW, high efficiency was 0.955, and Nusselt number (Nu) was 23.053. Conversely, HHO chose a rib-dominant hybrid design (model value 0.645) with a 400 ml/min flow rate. This design lowered thermal resistance to 0.7609 K-cm 2 /W, improving cooling performance, but it also increased pumping work (376 mW) and decreased efficiency (0.8835). Nusselt was 21.59, slightly lower. The effect of nanofluids, specifically water-based Al₂O₃ nanofluids, was examined in FMCHS under various Reynolds numbers (1000-3000) and a bottom heat flux of 50 W/cm² in order to further enhance the thermal performance. According to the findings, heat transport was significantly improved by nanofluids, quadrupling the Nusselt number at Re=3000. Increased viscosity and density resulted in a larger pressure drop, but the overall performance evaluation criterion (PEC) was greatly enhanced, demonstrating the thermophysical advantages of using nanoparticles. The idea that integrating bio-inspired geometries, nanofluid cooling, and AI-based optimisation provides a revolutionary route for the next generation of ultra-compact, high-efficiency thermal management systems is essentially supported by this collective body of research.