Terrestrial and Micro-Gravity Studies in Electrohydrodynamic Conduction-Driven Heat Transport Systems Public
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Electrohydrodynamic (EHD) phenomena involve the interaction between electrical and flow fields in a dielectric fluid medium. In EHD conduction, the electric field causes an imbalance in the dissociation-recombination reaction of neutral electrolytic species, generating free space charges which are redistributed to the vicinity of the electrodes. Proper asymmetric design of the electrodes generates net axial flow motion, pumping the fluid. EHD conduction pumps can be used as the sole driving mechanism for small-scale heat transport systems because they have a simple electrode design, which allows them to be fabricated in exceedingly compact form (down to micro-scale). EHD conduction is also an effective technique to pump a thin liquid film. However, before specific applications in terrestrial and micro-gravity thermal management can be developed, a better understanding of the interaction between electrical and flow fields with and without phase-change and in the presence and absence of gravity is needed. With the above motivation in mind, detailed experimental work in EHD conduction-driven single- and two-phase flow is carried out. Two major experiments are conducted both terrestrially and on board a variable gravity parabolic flight. Fundamental behavior and performance evaluation of these electrically driven heat transport systems in the respective environments are studied. The first major experiment involves a meso-scale, single-phase liquid EHD conduction pump which is used to drive a heat transport system in the presence and absence of gravity. The terrestrial results include fundamental observations of the interaction between two-phase flow pressure drop and EHD pump net pressure generation in meso-scale and short-term/long-term, single- and two-phase flow performance evaluation. The parabolic flight results show operation of a meso-scale EHD conduction-driven heat transport system for the first time in microgravity. The second major experiment involves liquid film flow boiling driven by EHD conduction in the presence and absence of gravity. The terrestrial experiments investigate electro-wetting of the boiling surface by EHD conduction pumping of liquid film, resulting in enhanced heat transfer. Further research to analyze the effects on the entire liquid film flow boiling regime is conducted through experiments involving nanofiber-enhanced heater surfaces and dielectrophoretic force. In the absence of gravity, the EHD-driven liquid film flow boiling process is studied for the first time and valuable new insights are gained. It is shown that the process can be sustained in micro-gravity by EHD conduction and this lays the foundation for future experimental research in electrically driven liquid film flow boiling. The understanding gained from these experiments also provides the framework for unique and novel heat transport systems for a wide range of applications in different scales in terrestrial and microgravity conditions.
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