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.