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Challenges Associated With Fan Cooled Electronics System Design
Keywords: CFD Software, computational fluid dynamics, cooling fan
Many electronics designers are challenged with the task of cramming many heat generating components into small fan cooled enclosures. Engineers have long realized that the assumption that a fan will create a specific flow rate inside of system based off of the system pressure resistance is not always true. It has been determine that the proximity of components, or any obstruction near the fan will degrade the ability of the fan to push air through the device regardless of the pressure resistance of the enclosure. This presentation will explore in detail the reason why this is happening, and discuss possible solutions that could help designers choose fans and place fans so that they will be more effective at cooling. Determining the right fan for a cooling application can be a challenging task. Just as your car’s fuel economy is probably not the same as reported on the window sticker (the EPA dyno test conditions are not the same as your real world driving conditions), the same thing can happen with cooling fans. Manufacturer fan performance curves are generated using blockage-free inlet and outlet conditions. In real life, most of today’s fan cooled electronics pack many components tightly around the fan, which affects the air flow and deteriorates the fan’s performance. Computational fluid dynamics (CFD) software has been determined to be a useful tool for helping engineers understand the thermal management of electronics. However, the accuracy of any CFD simulation is highly dependent on the assumptions, and geometry representation that is used in the simulation. Often it is not practical to model the intricate details of electronics when performing a thermal analysis. One simplification that is common practice in thermal modeling is to exclude fans from the geometry, and model the fan as a pressure loss regions. The region is defined using a manufacturer’s performance rating (P-Q curve) which is applied as the condition for the region thereby simplifying the set up, and shortening the computation time. While this method significantly simplifies the procedures and reduces the complexity of the simulation, it has been addressed by many engineers that a P-Q curve provided by a fan manufacture does not match with the actual performance especially when the fan is installed in the vicinity of other components which could completely change the flow behavior. This presentation introduces an innovative tool that allows an engineer to quickly and easily design a fan in 3D and to predict its performance including P-Q curve, power curve, and efficiency curve. As a result, the designer can design an optimized axial fan specific to the configuration of the system design.
Ben Cook,
Software Cradle Co.

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