As the state-of-the-art technology for energy saving, variable-frequency drives (VFDs) can be applied in nuclear power plant to drive recirculation pumps for coolant flow control. Due to requirement of high reliability, such as in nuclear industry, air natural convection cooling plays an important role in and while brings out a great challenge to thermal management for electronic unit. With an application of single board computer module in control system, another cooling challenge comes from heat flux increase caused from smaller footprint, since all of components, such as processor, chipset, memory and power supply etc., are built into one board. In the paper, cooling technologies for the single board computer module are investigated and developed, focusing on natural air heat convection from heat sink to ambient and heat conduction from board to heat sink. Based on thermal analysis associated with mechanical consideration, one heat sink is used to cool multiple components on the board. Two TIMs (thermal interface materials) and one heat spreader are employed for heat conduction from CPU and chipset to heat sink, respectively. Extrusion heat sink is selected with a comprehensive consideration of cost and thermal performance. A numerical simulation model is developed and validated against testing results. With the verified model, effects of fin arrangement on heat sink performance are analyzed. A study is conducted for optimization of base plate and fin thickness, and accordingly a heat sink is developed for the present application. Environmental conditions, such as temperature, altitude, and humidity etc., are analyzed to investigate their influence on cooling performance of natural air convection.

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