HEAT TRANSFER AND FLUID MECHANICS FROM A PIEZOELECTRIC FAN OPERATING IN ITS SECOND RESONANT FREQUENCY MODE
Piezoelectric fans are receiving increased interest for thermal management applications because of their reliability, minimal power consumption, and noise-free operation. These features are of particular interest to companies who have strict reliability constraints and have reached the thermal limit of conventionally used natural convection heat sinks. For a classical piezoelectric fan operated at its primary resonance frequency mode, the majority of airflow propagates from the fan tip. This type of airflow is advantageous if the heat source is positioned perpendicular to the long side of the fan, however if the heat source is parallel to the fan these advantages are not observed. This paper investigates the fluid mechanics and heat transfer from a fan operating at its secondary resonant frequency mode. The objective was to generate superior airflow and cooling when the fan is positioned parallel to a heated surface. The piezoelectric fan used in this study is a 12.7mm x 110mm fan with the second resonant mode at 77Hz. A custom built experimental facility was developed to capture both the fluid flow fields from the fan using Particle Image Velocimetry (PIV) and the subsequent thermal patterns that occur on a heated surface with infrared imaging. A constant heat flux foil was employed to capture the full field infrared measurements. The results show two jets are formed in opposing directions emanating from the midsection of an unconfined fan in free space. Enhanced heat transfer is observed on the heated foil caused by the impingement of the lower jet. The results found in this paper show that there are advantages to operating the fan at its second resonant frequency mode.