Enhancing heat transfer in air-cooled heat sinks using piezoelectrically-driven agitators and synthetic jets

Air-cooled heat sinks are widely used for microelectronics cooling. Piezoelectrically-driven agitators and synthetic jets (syn-jets) have been reported as good options in enhancing heat transfer on nearby surfaces. This study proposes that agitators and syn-jets be integrated within air-cooled heat sinks to significantly augment heat transfer performance. The proposed integration is investigated experimentally and computationally in a single-channel heat sink with one agitator and two syn-jet arrays. The study of a single channel between two fins is a precursor to the design of a full scale, multi-channel heat sink. The agitator and syn-jet arrays are separately driven by three piezoelectric stacks operating at their individual resonant frequencies to actively disrupt and mix the bulk air flow within the channel. The experiments show that the combination of the agitator and syn-jets raises the heat transfer coefficient of the channel by 82.4%, compared with a same channel having channel flow only. The computations show similar rises that agree well with the experiments. The numerical simulations attribute the active heat transfer enhancement to the turbulence introduced in the channel flow near the tips of the fins which constitute the channel walls by the syn-jets and the vortices introduced in the channel flow near the side and base of the channel walls by the agitator plate. Heat transfer enhancement by the agitator and syn-jets increases as their amplitude or frequency increases, but the increase percentage by these active components decreases as the channel flow velocity increases. A correlation between the average Nusselt number for the channel walls and the Reynolds numbers for the channel flow, agitator, and syn-jet is established.