Enhancement of forced convection heat transfer using aero-elastically fluttering reeds

Abstract

Heat transport within high aspect ratio, rectangular mm-scale channels of air cooled heat sinks is significantly enhanced by deliberate formation of unsteady small-scale vortical motions induced by autonomous, aeroelastic fluttering of cantilevered planar thin-film reeds. The interactions between the reed and the channel flow are exploited to overcome conventional limits of forced convection heat transport by substantial increases in the local heat transfer coefficient at the fins' surfaces, and in the mixing between the thermal boundary layers and the cooler core flow. This approach is demonstrated for improving the thermal performance of low-Reynolds number air-cooled heat sinks where the global air-side pressure losses can be significantly reduced by lowering the required air volume flow rate for given heat flux and surface temperature. The thermal performance enhancement is investigated in a mm-scale model of the rectangular heated fin channels. Of particular interest are the increases in power dissipation and the associated fluid power over a range of flow rates and reed lengths. It is shown that the reed flutter increases the turbulent kinetic energy of the flow even when the base flow undergoes transition to turbulence and consequently their effectiveness as may be measured by the decrease in the thermal resistance and increase in the global Nusselt Number that rises with Re.