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Thesis (M.S.)--Rutgers University, 2010. / "Graduate Program in Mechanical and Aerospace Engineering." Includes bibliographical references (p. 101-104).

Thesis (Ph.D.)--McMaster University, 2001 / Includes bibliographical references (leaves 242-250). Also available via World Wide Web.

Alternating current electrohydrodynamics (ac-EHD) has been reported as a promising technique for enhancing sensor performance by the intimate mixing of the analyte solution at the electrode surface. The lateral fluid motion created by the ac-EHD phenomenon can be tuned by changing the frequency, voltage, and electrode geometry. To date, various studies have been conducted on the use of 2D electrodes based ac- EHD devices for sensor applications. However, the use of 3D electrodes may provide better fluid mixing as compared to the 2D electrodes due to the high surface area of the electrodes. To test this hypothesis, 2D and 3D microelectrodes with different sizes were designed and fabricated for ac-EHD studies using standard lithography and etching processes. Previous methods to achieve 3D microstructures and common issues faced during fabrication are also discussed. The lateral fluid motion created by the 2D and 3D electrodes after the application of different voltages and frequencies was analyzed by tracking the motion of fluorescent beads present in the mixing fluid. Fluorescence microscopy technique was used to capture videos of the movement of fluorescent beads in the fluid. The videos were analyzed using ImageJ to calculate the speed of fluorescent beads in the case of 2D and 3D electrodes. Furthermore, a different pattern of the fluid motion was observed in the case of 3D electrodes, which highlights the complex fluid movement in the case of 3D electrodes as compared to the 2D electrodes.

published_or_final_version / Electrical Engineering / Doctoral / Doctor of Philosophy

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.