PERFORMANCE CHARACTERIZATION OF POOL BOILING ON INNOVATIVE FOAMS AND MICRO STRUCTURED SURFACES - APPLICATION TO DIRECT IMMERSION COOLING OF ELECTRONICS
Gershen, Lewis Elliot
Ohadi, Michael M
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This thesis is an experimental investigation of the thermal performance during boiling on copper foam and copper-finned microstructures as a thermosyphon evaporator. Copper foam is an open-celled porous media with interconnected copper ligaments of thermal conductivity up to 1.51 W/(cm2&#61655;K). The high thermal conductivity of this type of copper foam allows heat to rapidly spread through the foam causing widespread boiling. The boiling allows large transfers of energy from the heater (the source) to the working fluid (sink) with a low temperature difference between the heated surface and the working fluid. The thermal performance of the copper foams was investigated as a function of parametric values of foam height, pore density (pores per inch - PPI), and porosity. Data showed the pore density and porosity of the foam significantly affected heat transfer by changing the pore sizes and ligament sizes while thickness in the range of 1 to 5 mm had little effect on thermal performance. Surface tension is shown by dimensionless analysis to be the dominating force within the foam. The data also indicated the heat transfer coefficient for boiling HFE-7100 from copper foam ranged from 2,000 to 9,000 W/(m2&#61655;K). The copper foams provided significant heat transfer from the source. For example, copper foams provided heat loads up to 70 W/cm2 at 90 oC superheat. The second set of experiments in the present study involved testing of micro-finned structures. For such surfaces the important parameters we paid attention to were fin density (fins per inch) and aspect ratio (ratio of channel height to channel width) of the copper-finned microstructures. The data showed that aspect ratio and fin density substantially affect heat transfer performance through different channel cross-section sizes. The heat transfer provided by the micro-finned structures was substantially enhanced. For example, copper-finned microstructures provided heat loads up to 43 W/cm2 at 20 oC superheat. In this thesis, many chapters will discuss the reasoning behind this study and the results of it. The first chapter will cover the motivation and background information for this work. The next chapter discusses the experimental setup and how the results were obtained. The third chapter will review the results of the copper foams and discuss the cause of the results. The fourth chapter discusses the thermal performance of micro-finned structures. Finally, the conclusions of this study and suggested future work will be presented in the last chapter.