Enhanced Heat Transfer in Heat Sink Channels using Autonomously Fluttering Reeds

Low Reynolds (Re) number forced convection heat transport within channels of compact high-performance heat sinks is enhanced by deliberate formation of unsteady, small-scale vortical motions that lead to significant increases in the heat transfer coefficient at the channel walls and the mixing between the wall thermal boundary layers and the cooler core flow. These motions are induced by the interactions between autonomous, aero-elastically fluttering cantilevered thin-film reeds and the channel flow. The thermal performance enhancement by reed flutter is investigated in a mm-scale, modular model of the heatsink channels with emphasis on the increases in local and global heat transfer characteristics (Nusselt number, Nu) and associated losses over a range of flow rates and channel heights. It is shown that the increase in local and global Nu is accompanied by increases in the turbulent kinetic energy and is sustained over a range of Re that encompasses laminar, transitional, and turbulent base flows with minor corresponding increases in flow losses. The increase in Nu in the presence of the reed leads to a significant reduction in channel wall temperature at a fixed heat dissipation (Q), or, alternatively, to significantly higher Q at a fixed wall temperature. It is shown that the incremental flow losses induced by the reed depend primarily on its planform scales and oscillation frequency which are characterized by its Strouhal number $(St=\Phi L/U).$ However, because Nu depends weakly on St, the flow losses can be minimized to yield high thermal enhancement efficiency.