Direct Actuation of Small-Scale Motions for Enhanced Heat Transfer in Heated Channels

Abstract

Flow-effected, enhanced heat transfer in a high aspect ratio rectangular mm-scale channel that models a segment of a high-performance, air-cooled heat-sink is characterized. The present investigation reports a novel approach to enhanced cooling without increasing the channel’s characteristically low Reynolds number. Heat transport that is governed by the local heat transfer from the fin surface and by subsequent mixing with the core flow is significantly increased by deliberate shedding of unsteady small-scale vortices that are induced by the vibration of a miniature, planar piezoelectric reed. The present investigation focuses on the heat transfer and fluid mechanics that are associated with the small-scale motions induced by the reed. High-magnification particle image velocimetry (PIV) is used to characterize the interaction of the induced vortical structures with the channel flow. Performance enhancement by reed actuation is quantified in terms of increased power dissipation over a range of flow rates compared to the baseline flow in the absence of the reed. It is demonstrated that the channel’s coefficient of performance can be increased by a factor of 1.4 while accounting for the power to the reed and the changes in channel pressure drop.