Effect of driven frequency on flow and heat transfer of an impinging synthetic air jet

In this study, impingement heat transfer from a synthetic air jet on a heated surface was experimentally studied. A synthetic jet provides a high heat transfer coefficient and a compact design, which is suitable for the thermal management of electronic devices. The synthetic jet is produced by the high frequency oscillating motion (200-800 Hz) of a piezoelectric actuator, and a jet Reynolds number ranging from 500 to 1300. The instantaneous and time-averaged velocity profiles of the synthetic jet issuing from the jet hole were measured using a hot wire anemometer. The jet hole diameter was 3 mm and the jet-to-surface spacing (Z/d) ranged from 0 to 25. The excitation frequency effect, jet-to-surface spacing, and jet Reynolds number were tested. The heat transfer enhancement of the synthetic jet was at least double the natural convective heat transfer. At a small jet-to-surface spacing, the warm air circulates inside small spaces, jeopardizing heat transfer. An optimal driven frequency of 600 Hz in this study provided the highest jet flow rates and heat transfer enhancement.