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Enhanced heat transfer in air cooled heat sinks using aeroelastically fluttering reeds

The thermal performance of air cooled heat sinks is significantly enhanced by deliberate formation of unsteady small-scale vortical motions within the fin channels that result in significant increases in the local heat transfer coefficient at the fins' surfaces, and in the mixing between the thermal boundary layers and the cooler core flows. These small-scale motions are induced by autonomous aeroelastic fluttering of a cantilevered planar thin-film reed that is placed in the center plane of each fin channel. The thermal performance enhancement in the absence and presence of reed actuation is characterized in a mm-scale model of the rectangular air-cooled heated fin channels. Of particular interest are the increases in power dissipation and the associated fluid power over a range of flow rates. It is shown that the cooling flow rate that is needed to sustain a given heat flux at a fixed wall temperature is nearly two times lower in the presence of reed actuation. Therefore, the reeds can 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 relative to the base flow is similar to that of the model channel.