Small-Scale Vorticity Induced by a Self-Oscillating Fluttering Reed for Heat Transfer Augmentation in Air Cooled Heat Sinks

Abstract

Heat transfer in a high aspect ratio, rectangular mm-scale channel that models a segment of a high-performance, air-cooled heat-sink is enhanced by deliberate formation of unsteady small-scale vortical motions. These small-scale motions are induced by self-fluttering, cantilevered planar thin-film reeds that are placed along the channel’s centerline. Heat transfer is enhanced by significant increases in both the local heat transfer coefficient at the fins surfaces, and in the mixing between the thermal boundary layers and the cooler core flow. The present investigation characterizes the thermal performance enhancement by reed actuation compared to the base flow (in the absence of the reeds) in terms of increased power dissipation over a range of flow rates, along with the associated fluid power. It is shown that because the cooling flow rate that is needed to sustain a given heat flux at a given surface temperature is almost two times higher than in the presence of the reeds, the reeds lead to a four-fold increase in thermal performance (as measured by the ratio of power dissipated to fluid power). The thermal effectiveness of the reeds is tested in a multi-channel heat sink, and it is shown that the improvement in heat transfer coefficient of the base flow is similar to that of the single channel.