This thesis is missing page i, all other copies are missing this page as well. - Digitization Centre / Emergence of efficient cooling techniques has been a crucial factor in development of faster and more powerful electronic equipment and ICs. One of the key obstacles towards further miniaturization is efficient heat removal from regions of high temperature to maintain continued operation of these devices below their maximum operating range. Recently, a significant amount of research has been directed to develop liquid based cooling techniques. For example, microchannel heatsinks have been designed to remove up to 1 kW/cm2. Developing microscale actuators that provide sufficient pressure head is essential for integrating these microscale cooling schemes with the electronic devices. Different techniques can be used to pump fluid in the microscale such as electroosmotic, magnetohydrodynamic, and electrohydrodynamic (EHD) pumping. Among these technologies, EHD pumps are particularly promising for microfluidic devices because they use no moving parts, and uses very small power and has low cost and maintenance requirements. This work presents the development and test of EHD micropumps with different electrode configurations. Four different electrode configurations: (1) planar symmetric electrodes, (2) planar asymmetric electrodes, (3) 3-D symmetric electrodes, and (4) 3-D asymmetric electrodes were investigated. In addition, the effect of different design specifications, such as the inter-electrode spacing and spanwise spacing of the micropillars were investigated. The electrodes were fabricated using a two mask process. First, a thin layer of chromium was deposited on glass as a seed layer for gold electrodes. Positive photoresist (AZ P4620) was patterned to form the mould for the micropillar electrodes. Nickel was electroplated to fill the mold. Subsequently, a Cr/Au layer was patterned to devise the electrode base connector and pads. The microfluidic channels were fabricated by casting polydimethylsiloxane (PDMS) on top of an SU-8 100 (MicroChem Corp.) mould which was patterned to delineate the microchannel structure. The PDMS microchannel was integrated on the electrode base by plasma oxidizing the PDMS and glass wafer, and sealing the connection with liquid PDMS. The pump performance was experimentally determined with Methoxynonafluorobutane (HFE-7100) as the working fluid. All of the micropumps were tested under a no net flow condition to find the maximum pressure generation. The micropumps with planar and asymmetric planar electrode configurations were also tested for maximum flow rate under no imposed back pressure. The results show that the micropumps with the 3D asymmetric electrode design generated a higher pressure head compared to the other micropumps with identical inter electrode spacing under no flow conditions. The micropumps with planar asymmetric design had a higher performance compared to the micropumps with planar asymmetric electric under both no flow condition and no back pressure condition. A maximum pressure head of 2240 Pa was generated at an applied voltage of 900 V by the micropump with 3D asymmetric electrode design. A maximum flow rate of 0.127 mL/min was achieved by the micropump with planar asymmetric electrode configurations. This is five times higher than the maximum flow rate generated by the micropump with the planar symmetric electrode design. / Thesis / Master of Science (MS)

Standard eddy-viscosity models lack curvature and system rotation sensitized terms in their formulation. Hence they fail to capture the effects of curvature and system rotation on turbulence anisotropy. As part of this effort, an algebraic expression for a characteristic rotation term is developed and tuned with the help of rotating homogeneous shear flow. This formulation is primarily based upon the rotation and curvature sensitized eddy-viscosity coefficient developed by York et al. (2009). A new scalar transport equation loosely based on Durbin’s wall normal turbulent velocity scale (Durbin, 1991) is introduced to account for the modification in turbulence structure due to system rotation and curvature effects. The added transport equation also introduces history effects and stability in the solution with small increase in computational cost. The eddy-viscosity is redefined based on new turbulent velocity scale and hence the effects of rotation and streamline curvature are introduced into the mean momentum equation. A number of canonical test cases with significant curvature and rotation effects along with a cyclone flow, a representative of complex industrial flows, are considered for model validation. Hybrid modeling framework combines the strength of RANS in boundary layers and LES in separated shear layers to alleviate the weaknesses of RANS and limitations of LES model in some complex flows. A recently proposed hybrid RANS-LES modeling framework uses a weighing parameter that dynamically determines the RANS and LES regions based on solution statistics. The hybrid modeling methodology is implemented on a normal jet in crossflow, and a film cooling case for the purpose of model validation and evaluation. The final goal of the proposed effort is to combine advanced RANS modeling capability with LES using the new hybrid modeling framework. Specifically, the curvature and rotation sensitive RANS model developed here is coupled with commonly used LES models to produce a novel model for complex turbulent flows with the potential to improve accuracy of CFD predictions (versus existing RANS models) as well as significantly reduce the computational expense (versus existing LES models). Performance of the model form hence developed is evaluated on a cyclone flow case.