Synthetic jet's flow-induced vibrations for enhanced thermal management and energy harvesting

Abstract

An experimental study is conducted on a novel synthetic jet (SJ) design featuring integrated flaps, with the results compared to those of a conventional SJ. This study addresses the challenge of low heat transfer rates in confined spaces observed with conventional SJs. The flaps are introduced in the path of the SJ flow to mitigate the recirculation of the heated air and harness the energy of the flow. Additionally, piezoelectric materials placed on the flaps are able to harvest electricity from vortex-induced vibrations. The positioning of the flaps along the SJ's axial direction was varied to evaluate their impact on both heat transfer efficiency and energy harvesting performance. The experiments are carried out at constant frequency (32 Hz) and amplitude (8 V) to the SJ actuator, originating from a 20 mm orifice diameter. The generated flow corresponds to the Reynolds number and dimensionless stroke length of 11000 and 13.5, respectively. The flap-integrated SJ demonstrated up to 63 % greater heat removal in spot cooling compared to the conventional SJ. Hot-wire velocity measurements revealed that the flapping motion increased turbulence levels near the impingement region, thereby enhancing heat transfer. Additionally, the flaps restricted the return of heated air from the impinging surface to the orifice during the diaphragm's suction cycle. This mechanism disrupted the recirculation of heated air, resulting in a significantly higher heat transfer rate. The harvested power from piezoelectric material mounted on two flaps goes up to 240 μW, which could be useful in small-powered devices and sensors. The proposed flap SJ's design significantly improves heat transfer compared to the conventional SJ, while also enabling additional energy harvesting. © 2024