NUMERICAL ANALYSIS OF 3D MICROCHANNEL HEAT SINK UNDER VARYING HEAT FLUX, REYNOLDS NUMBER AND NANOPARTICLE CONCENTRATION

Abstract

This thesis undertakes a numerical study by employing a unit cell approach for three-dimensional fluid flow and heat transfer in micro-channel heat sinks. Two configurations were simulated: a traditional straight rectangular microchannel and a novel design featuring circular bumps spaced evenly along the channel walls. The numerical simulations were carried out using ANSYS Design Modeler and Fluent, and the computed results were validated with existing experimental data. Both configurations' thermal and hydrodynamic characteristics were assessed for changing Reynolds numbers (100–900) and imposed heat fluxes (100, 150, and 200 W/cm²), and water and Al₂O₃-water nanofluids of 1.5% and 2.5% volume concentrations as working fluids. Microchannels were represented by oxygen-free copper walls because of its high thermal conductivity. Results show that raising the Reynolds number has a remarkable effect on convective heat transfer, resulting in lower temperature differences across the inlet and outlet (ΔT = Tout – Tin). The bumped geometry showed consistently better thermal performance than the straight channel owing to added surface area and flow disturbances that promote mixing and heat transfer. For example, at Re = 500, the surface temperature increases of 25% and 34% and the outlet temperature increases of 50% and 33% were observed, respectively, over heat flux ranges of 100–150 W/cm² and 150–200 W/cm². Enhancement was even more noted with the inclusion of Al₂O₃ nanoparticles in the base fluid. At 1.5% concentration in bumped geometry, surface temperatures increased by 35% and 25%, whereas outlet temperatures increased by 35% and 37% for the same flux ranges. The same trends were noted for 2.5% concentration. The bumped design had greater pressure drops, particularly at high Reynolds numbers, but had a good pressure loss versus heat removal efficiency trade-off.