Effect of leading edge geometry on the performance of plate fin heat sinks in forced convection at transitional Reynolds numbers

This study analyses the effect that leading edge geometry has on the thermal performance of plate fin heat sinks in forced convection. The range of Reynolds numbers studied covers the so-called transitional flow regime, where laminar- turbulent transitional flow can exist even above critical Reynolds numbers. Plate fins with sharp (rectangular) and rounded leading edges are considered. 2D numerical analysis on forced convection over the fins is carried out in ANSYS Fluent using the Transition SST turbulence model to capture transitional effects. At lower Reynolds numbers, a fully laminar boundary layer exists along both the sharp and rounded fins, with the sharp fin exhibiting slightly lower heat transfer rates and higher flow resistance due to large flow separation at its leading edge. Above a critical Reynolds number, separation-induced transition occurs at the leading edge of the sharp fin, creating a turbulent boundary layer along the fin. This increases the average Nusselt number of the sharp fin by 58 - 186% relative to the rounded fin. Using a Quality Factor metric, defined as the ratio of heat transfer rate to pumping power across the fin, the sharp fin was found to have a 24.6 - 70.1% higher thermal efficiency than the rounded fin above the critical Reynolds number. These results suggest that in the transitional flow regime, a sharp leading edge increases the thermal performance of plate fin heat sinks by promoting turbulent forced convection along the fins.