Impact of Channels Aspect Ratio on the Heat Transfer in Finned Heat Sinks with Tip Clearance

A 3D numerical study is used to analyze the flow topology and performance, in terms of heat transfer efficiency and required pumping power, of heat sink devices with different channel aspect-ratio in the presence of tip-clearance. Seven different channel aspect ratios [Formula: see text] , from 0.25 to 1.75, were analyzed. The flow Reynolds numbers [Formula: see text] , based on the average velocity evaluated in the device channels region, were in the range of 200 to 1000. Two different behaviors of the global Nusselt were obtained depending on the flow Reynolds number: for [Formula: see text] , the heat transfer increased with the channels aspect ratio, e.g., for [Formula: see text] , the global Nusselt number increased by 14% for configuration [Formula: see text] when compared to configuration [Formula: see text]. For [Formula: see text] , the maximum Nusselt is obtained for the squared-channel configuration, and, for some configurations, flow destabilization to a unsteady regime appeared. For [Formula: see text] , Nusselt number reduced when compared with the squared-channel device, 11% and 2% for configurations with [Formula: see text] and 1.75, respectively. Dimensionless pressure drop decreased with the aspect ratio for all cases. In the context of micro-devices, where the Reynolds number is small, these results indicate that the use of channels with high aspect-ratios is more beneficial, both in terms of thermal and dynamic efficiency.