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a b s t r a c tHeat transfer and pressure drop characteristics of micro pin fin arrays in a narrow rectangular channel with an air through flow are studied with different flow rates ranging from laminar to turbulent flow.Copper micro pin fins 150-400 lm long and 75-700 lm in diameter are fabricated by microfabrication techniques. Performance ratios that compare heat transfer to pressure drop characteristics are evaluated to investigate performance of the micro pin-fin surfaces when both heat transfer and pressure drop are important. The results indicate that fluid dynamic effects generated around micro pin fins take a more dominant role for heat transfer enhancement than the area increase due to micro pin fins. A maximum heat transfer enhancement of 79% over plain surface is achieved due to a micro pin-fin surface with a height of 250 lm and a diameter of 400 lm. It is expected that the micro pin-fin surfaces can be used for improving cooling performance of fan-assisted heat sinks for electronics thermal management.

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.

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