Nanofluid-Enhanced Biomimetic Liquid-Cooled Heat Sinks for Efficient Thermal Management Applications

The escalating demand for compact, high-performance electronic devices, driven by the rapid advancement of artificial intelligence, electric vehicles, and data-intensive technologies, has imposed significant thermal management challenges. Traditional air-cooled and straight-channel liquid cooling systems are increasingly inadequate in addressing the high heat fluxes generated by these technologies, particularly when operating under space, energy, and sustainability constraints. This thesis addresses the urgent need for efficient, scalable, and adaptive cooling solutions through the experimental development and evaluation of novel biomimetic liquid-cooled heat sink designs integrated with nanofluid technology. This research adopts an interdisciplinary approach, combining thermofluids, materials science, and biomimetic design. It introduces a new concept in heat sink design inspired by the fluid dynamics of aquatic organisms such as tuna and the black ghost knifefish, novel heat sink designs were conceived to optimise flow dynamics, reduce pressure loss, and maximise heat transfer. These designs depart from traditional linear geometries, encouraging researchers to view nature as a blueprint for rethinking engineering solutions. The bioinspired hybrid pin-fin geometries were designed, fabricated, and optimised under varying operating conditions. The final optimised Staggered Arranged Airfoil Integrated Split Corrugated Curvilinear Pin-Fin (SAISCCPF) configuration create secondary flow paths, enhance mixing, and promote turbulence, thereby improving heat transfer performance while providing alternative passages in case of channel blockage. A series of quantitative, experimental investigations were carried out to examine the hydrothermal performance of different heat sink configurations under varying Reynolds numbers and heating powers. The study began with straight-channel and inline pin-fin configurations, then advanced to staggered and split-fin biomimetic designs. Using a custom-built test facility, the experiments evaluated key performance parameters including Nusselt number, pressure drop, wall temperature, thermal resistance, and temperature distribution. The experimental methodology was rigorously validated, and data was collected across a broad range of flow rates and thermal loads to ensure robustness and repeatability. Parallel to the heat sink design investigations, this work also involved the formulation and testing of mono, binary, and tri-hybrid nanofluids. These nanofluids were based on carefully selected nanoparticles include metallic (silver, Ag), ceramic (aluminium nitride, AlN; silicon carbide, SiC; beryllium oxide, BeO), and carbon-based (multi-walled carbon nanotubes, MWCNTs) materials, each chosen for their unique combination of thermophysical properties, particle morphology, cost, and chemical compatibility with water. The nanofluids were prepared using a two-step method involving ultrasonication and surfactant-assisted dispersion to ensure long-term colloidal stability and avoid agglomeration, a critical factor for maintaining consistent thermal and hydraulic performance. The research was structured into two phases. In the first phase, mono and hybrid nanofluids based on Ag, BeO, and SiC were synthesised and tested. Among these, Ag-based nanofluids delivered the highest thermal conductivity improvement of approximately 6.95%, while BeO offered minimal viscosity increase, and SiC provided a cost-effective compromise. Hybrid nanofluids such as Ag–SiC (60:40) achieved conductivity gains up to 7.43% with balanced hydraulic performance. A subsequent study focused on nanofluids containing MWCNTs, Ag, and AlN. While MWCNTs exhibited superior heat transfer capability, they suffered from stability issues. Tri-hybrid nanofluid MWCNTs/Ag/AlN, particularly the formulations 20:40:40 and 20:60:20, demonstrated an optimal combination of high thermal conductivity, suspension stability, and manageable viscosity, emerging as the most promising formulation. Phase II involved experimental thermal-hydraulic evaluation of the nanofluids developed in Phase I, applied across novel biomimetic heat sink designs. The phase began by testing a conventional straight-channel heat sink with a hydrophobic-coated surface using water. While the hydrophobic treatment moderately reduce pressure drop, limitations remained in improving heat transfer. This was followed by a comparative study with the newly designed Airfoil Integrated Corrugated Curvilinear Pin-Fin (AICCPF) configuration. The results showed an approximately 103% improvement in Nusselt number, while the pressure drop also increased by around 37.5% compared to the straight-channel design. These enhanced biomimetic configurations were then evaluated using Ag, BeO, and SiC nanofluids and their hybrids. Ag-based fluids once again demonstrated the best thermal performance, while BeO continued to show minimal flow resistance. Among hybrids, Ag–SiC mixtures sustained high Nusselt number enhancements with manageable pressure drop penalties, especially under the SAICCPF geometry. In the final stage, the optimised heat sinks were tested using MWCNTs, Ag, and AlN nanofluids including mono, binary, and tri-hybrid formulations. The SAISCCPF configuration, coupled with the (20:60:20) tri-hybrid nanofluid, achieved the best overall performance with a Nusselt number enhancement of around 17% at 325 W. While the pressure drop increased modestly to approximately 475 Pa, this was justified by the substantial thermal gains and enhanced flow distribution. The design's multi-path structure and local swirl generation proved effective in maintaining particle suspension, reducing agglomeration, and maximising convective performance across all tested fluids and conditions. This thesis contributes a foundational understanding of hybrid nanofluid behaviour in complex geometrical domains and provides robust experimental data to support future designs. Future research is encouraged to explore long-duration cyclic stability of these nanofluids under operational loads, adaptation of these concepts to dynamic cooling systems (e.g., thermosyphons, phase change materials (PCM), pulsating heat pipes), and full-scale prototyping in data centres, EV batteries, or power electronics environments.