Application of Microporous Coating in Passive Thermal Management Device




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Developments in electronic applications present numerous thermal management challenges for the dissipation of waste heat. The work presented in this dissertation is applicable to the dissipation of persistent heat from large areas and the spreading of waste heat from highly concentrated heat sources. Persistent uniform heat generation from a relatively large area is encountered in the use of batteries for electric vehicles among many other applications. In these applications, heat must be dissipated from a relatively large surface area, relative to the spacing between two adjacent heat sources. Highly concentrated heat sources are increasingly encountered due to the rapid development of electronic packaging techniques. Specifically, the overall system power densities continue to increase due to the size minimization trend of the electronic devices. These applications result in significant thermal management challenges. If not managed properly, increased temperatures can cause significant deterioration in a device’s performance and greatly reduce the product reliability. Traditional active cooling strategies, such as singlephase and two-phase active cooling systems, using pumps or compressors as auxiliary components, dissipate reasonably high heat fluxes and can be applied over large areas. However, the associated auxiliary devices increase the system’s complexity and decrease its reliability. Alternatively, passive cooling devices utilizing liquid-vapor phase change thermal systems, such as thermal ground plane (TGP), effectively dissipate or spread the heat. These can be wick type or wickless and rely on evaporation or boiling phase change. The wick type TGP or vapor chamber utilizes capillary forces to recirculate the evaporating liquid, the wicking structure plays an essential role in the overall heat dissipation effectiveness. For the wickless type TGP, which utilizes a bubble pumping mechanism to circulate the liquid instead of wicking, boiling heat transfer performance is dominant. In the current dissertation, firstly, the performance of an aluminum high-temperature, highconductive microporous coating, which can be used in wick-type thermal ground plane as the wicking material, is characterized through mass and heat transfer experiments utilizing water and highly wetting fluids for dissipating persistent heat from large areas. Secondly, the wettability effect on the nucleate boiling heat transfer performance of a copper high-temperature, thermally conductive, microporous coating is experimentally investigated. Thirdly, a wickless and orientation independent ultra-thin thermal ground plane is developed using this copper high-temperature, thermally conductive, microporous coating for spreading highly concentrated waste heat.



Engineering, Mechanical