An experimental and computational investigation of a thin piezofan cooler

Recent trends in electronic cooling systems are targeted towards a reduction in size, therefore small form factor/miniature cooling devices are of interest to various applications. Among these devices are piezoelectric fans which are simply made of vibrating plates and shed vortices from their leading edge and enhance heat transfer from nearby target surfaces. This paper investigates the flow and temperature fields produced by a piezoelectric fan. An experimental study is performed to determine the temperature distribution of a vertically heated surface under various fan tip-to-target surface distances and driving conditions of the piezoelectric device (frequency). 2-D numerical simulations are carried out to predict the momentum and temperature fields in the domain of interest under the same boundary conditions of the experimental effort. The numerical results are in reasonably good agreement with the measured experimental data. The relevant dimensionless parameters such as Nusselt, Strouhal, and Keulegan-Carpenter numbers are determined. With a maximum Nusselt number of 20 and 57 for mylar and metallic piezo fans, respectively, the corresponding Strouhal, and Keulegan-Carpenter numbers suggest that a vortex formation occurs at the blade tip, however these vortices are weak such that they are neither able to approach the target surface as high strength structures nor improve heat removal significantly for the range of measurements.