Enhancing Heat Transfer of Air-Cooled Heat Sinks Using Piezoelectrically-Driven Agitators and Synthetic Jets

Abstract

Air-cooled heat sinks prevail in microelectronics cooling due to their high reliability, low cost, and simplicity. But, their heat transfer performance must be enhanced if they are to compete for high-flux applications with liquid or phase-change cooling. Piezoelectrically-driven agitators and synthetic jets have been reported as good options in enhancing heat transfer of surfaces close to them. This study proposes that agitators and synthetic jets be integrated within air-cooled heat sinks to significantly raise heat transfer performance. A proposed integrated heat sink has been investigated experimentally and with CFD simulations in a single channel heat sink geometry with an agitator and two arrays of synthetic jets. The single channel unit is a precursor to a full scale, multichannel array. The agitator and the jet arrays are separately driven by three piezoelectric stacks at their individual resonant frequencies. The experiments show that the combination of the agitator and synthetic jets raises the heat transfer coefficient of the heat sink by 80%, compared with channel flow only. The 3D computations show similar enhancement and agree well with the experiments. The numerical simulations attribute the heat transfer enhancement to the additional air movement generated by the oscillatory motion of the agitator and the pulsating flow from the synthetic jets. The component studies reveal that the heat transfer enhancement by the agitator is significant on the fin side and base surfaces and the synthetic jets are most effective on the fin tips.