Heat transfer enhancement in high-power heat sinks using active reed technology

Enhanced heat transfer in a high aspect ratio channel that models a segment of a novel, high-performance air-cooled heat-exchanger system for high-power electronics is characterized. Two innovative features that enable this system are integration of a centrifugal blower-diffuser with a high-density finned heat-sink, and microfabricated active reed elements that provide small-scale heat transfer enhancement at the reduced air flow rates. The present investigation focuses on the heat transfer and fluid mechanics that are associated with the small-scale motions induced by a piezoelectric vibrating reed that is integrated within a mm-scale channel. These time-periodic small-scale motions enhance convective heat transfer at the channel surfaces and the mixing of the thermal boundary layers with the core flow. High-magnification particle image velocimetry (PIV) measurements are used to characterize the interaction of the vortical structures shed by the reed with the channel wall and the induced small-scale motions. 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.