Flow and heat transfer study of an impinging piezoelectric fan over a vertical surface

Abstract

Piezoelectric fans are low-form-factor cooling devices, which have gained recent attention for electronics cooling. These devices feature a vibrating blade, which sheds vortices from its tip during its motion. The performance of a piezoelectric fan is based on its location, orientation, and operating condition. Thus, we investigated the heat transfer and flow field of an impinging flow produced by a piezoelectric fan. The heat transfer tests are conducted using a vertical, 2.54 cm × 2.54 cm copper heater, which is configured with the piezoelectric fan positioned along its centerline. The fan is operated at its fundamental frequency of 60 Hz, where it achieves maximum heat transfer and fan deflection. There is significant heat transfer degradation with increasing heater-to-fan spacing and off-resonance operating conditions. To better understand this thermal performance, we require information about the flow field produced by this pulsating flow. Hence, we performed particle image velocimetry (PIV) measurements of the flow field for free and impinging cases with different heater-to-fan spacing. We used instantaneous and time-averaged PIV to depict the response in a region within approximately two times the fan oscillation amplitude. In this region, there was a stagnation flow close to the heater, which would result in significant heat transfer. However, this flow also featured high-magnitude velocity vectors towards the sides of the heater rather than towards its center, which would likely result in non-uniform heat transfer.