Cooling High-Power LEDs With Piezoelectric Fans

Research project in conjunction with Siemens AG. The project’s goal is to cool a high-powered LED, simulated with resistive heaters attached to an aluminum block, from 100 ºC down to the 50-60 ºC range. Siemens requested that the solution be mechanically robust (>20,000 hours of life), minimal acoustic output (<45 dB), and scalable. As such, piezoelectric fans were selected as the primary mode of forced convection and the challenge was designing a heatsink to optimize airflow and maximize the total convective coefficient of the package.
Airflow from the piezoelectric fan was characterized through finite element analysis in COMSOL, hot-wire anemometry, and particle image velocimetry. Once flow was properly characterized, multiple heatsinks were designed and iterated in order to maximize heat transfer to the surroundings while minimizing heatsink volume. Aluminum was selected for the heatsink because of its relatively low-cost (as compared to copper), high coefficient of conduction, and die-castability. Heatsinks were prototyped using a combination of 3D printing and CNC machining and tested using a custom setup that allowed the fan to be cycled through different distances in two directions. As a result, optimal distances between the fan to heatsink surface and fan to heatsink edge were discovered. The effect of anodizing the heatsink black in order to control emissivity and maximize radiant heat transfer was also explored, but the cost increase was prohibitive as compared to the decrease in steady-state temperature.
The final heatsink and piezoelectric fan package exceeded the design goal and resulted in a steady-state temperature of 39 ºC. A paper on the findings will be published soon and a link will be provided on this page.
BMI Researchers

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