This research aims to identify optimal pin fin shapes that minimize flow pressuredrop and maximize heat transfer performance while investigating the influence of genetic algorithm (GA) parameters on these shapes. The primary goal is to discover innovative pin fin configurations through the use of a GA, moving away from traditional circular cylindrical designs. The study also examines GA parameters, including population size, generation size, selection methods, crossover rates, tournament size, and elite counts. A physical condition considered in this study is a rectangular channel with a square cross-section integrated with 10 pin fins, operating at a Reynolds number of 2316, and subjected to a heat flux of 5 W/cm2 at the bottom surface. Overall, the research seeks to enhance the energy efficiency of a liquid cooling system, with potential applications in the thermal management of computing devices. By enabling operating at significantly lower power, the optimized cooling system promises to reduce energy consumption and operational costs.

This dissertation investigates the complex dynamics of semi-dilute inertial particles suspended in vortices using the Eulerian-Lagrangian method. The study explores the modulation of flow induced by inertial particles, focusing on the characteristics of a single vortex, instability analysis within particle-laden flows, and the merging process of co-rotating vortices. Simulations reveal a preferential concentration mechanism, where inertial particles cluster around a void fraction bubble, accelerating the decay of the vortex tube. Small-scale clusters, arising from particle-trajectory crossings, induce significant gradients in the fluid vorticity field, contributing to rapid vortex breakdown. Within a specific Stokes number range, increased particle inertia results in faster vortex decay and stronger inhomogeneity in the particle phase. The instability mechanism in particle-laden flows is explored using a Rankine vortex model. Two-way coupling triggers azimuthal perturbations, leading to the breakdown of the vortex structure. Linear Stability Analysis and Two-Fluid modeling demonstrate that the dusty vortex flow exhibits unstable modes, with growth rates increasing with wavenumber. Eulerian-Lagrangian simulations validate these results, showing excellent agreement between computed and predicted growth rates. The dissertation also delves into the co-rotating vortex merger in a semi-dilute dusty flow. For weak inertial effects, merger experiences a delay compared to particle-free vortices. Under moderate inertial conditions, the merger process exhibits repulsion, increased separation, and eventual convective merger stages. Highly inertial particles stretch the vortex core, initiating a merger with an outcome of a particle-free vortex core surrounded by a halo of concentrated particles. In conclusion, the feedback force from the dispersed phase induces instability and significantly influences the dynamics of vortices in particle-laden flows. The findings contribute to a deeper understanding of the intricate interactions between inertial particles and vortical structures.

The Tesla valve, originating from Nikola Tesla's "valvular conduit" patent in 1920, offers a unique solution to fluid control challenges by enabling unidirectional flow while impeding reverse flow. With applications ranging from fluid pumps to high-power engines, Tesla's design functions as a fluidic diode, inducing pressure drops across the valve to define its efficiency through diodicity. Through computational fluid dynamics (CFD) simulations using ANSYS Fluent, the impact of removing the bifurcated section on Tesla valve efficiency is explored. The T45-R, D-Valve, and GMF Valve designs are analyzed across a range of Reynolds numbers (Re). Results show that while the absence of bifurcation can lead to higher diodicity values due to increased flow divergence and vortex formation, efficiency varies depending on flow conditions. The T45-R valve exhibits linear diodicity increase with Reynolds number, plateauing at higher values due to reduced fluid inertia influence. Conversely, the D-Valve with bifurcation excels at lower Re values, while the non-bifurcated version proves more efficient at higher Re values. The GMF Valve with bifurcation demonstrates efficiency at lower Re values but decreases in effectiveness as Re rises, with the non-bifurcated version showing lower efficiency overall. Overall, this research provides insights into the fundamental physics and design considerations of Tesla valves, offering guidance for optimizing fluid control applications across diverse industries. The study underscores the importance of considering geometric variations and flow conditions when designing Tesla valves for specific applications, highlighting the intricate relationship between valve geometry, flow dynamics, and efficiency.

This thesis aims to determine how finite wing aerodynamic loads change in proximity to the ground. In this study, the primary design tool is an inviscid panel method code, VORLAX. The validation tool is a commercial volume grid CFD package, ANSYS FLUENT. I use VORLAX to simulate wings with different incidences and aspect ratios to look at how ground effect impacts spanwise loading and incipient flow separation. Then the results were compared to widely published equations such as McCormick, Torenbeek, and Hoerner & Borst. Because I found that these “famous” equations function best only for specific conditions, I propose a new empirical equation to estimate ground effect lift as a function of aspect ratio and incidence. Using Stratford’s method to predict signs of flow separation in the inviscid solutions, I found that variations in the height above the ground were not significant enough to change the stall angle of low aspect ratio wings. I did find early signs of flow separation with increasing aspect ratio. I observe significant changes in spanwise loading when in ground effect; as I narrow the gap, the transverse loading builds higher near the center of the wing. These effects were more apparent in wings with smaller aspect ratio; higher aspect ratio wings experience a higher loading gradient near the tips in proximity to the ground. I found that high aspect ratio wings have a smaller stall angle compared to that of lower aspect ratio wings; these trends are consistent between the potential flow solution and the volume grid CFD viscous solution.

Heusler alloys were discovered in 1903, and materials with half-metallic characteristics have drawn more attention from researchers since the advances in semiconductor industry [1]. Heusler alloys have found application as spin-filters, tunnel junctions or giant magnetoresistance (GMR) devices in technological applications [1]. In this work, the electronic structures, phonon dispersion, thermal properties, and electrical conductivities of PdMnSn and six novel alloys (AuCrSn, AuMnGe, Au2MnSn, Cu2NiGe, Pd2NiGe and Pt2CoSn) along with their magnetic moments are studied using ab initio calculations to understand the roots of half-metallicity in these alloys of Heusler family. From the phonon dispersion, the thermodynamic stability of the alloys in their respective phases is assessed. Phonon modes were also used to further understand the electrical transport in the crystals of these seven alloys. This study evaluates the relationship between materials' electrical conductivity and minority-spin bandgap in the band structure, and it provides suggestions for selecting constituent elements when designing new half-metallic Heusler alloys of C1b and L21 structures.

Failures in the cold chain, the system of refrigerated storage and transport that provides fresh produce or other essentials to be maintained at desired temperatures and environmental conditions, lead to food and energy waste. The mini container (MC) concept is introduced as an alternative to conventional refrigerated trucks (“reefers”), particularly for small growers. The energy consumption and corresponding GHG emissions for transporting tomatoes in two cities representing contrasting climates is analyzed for conventional reefers and the proposed mini containers. The results show that, for partial reefer loads, using the MCs reduces energy consumption and GHG emissions. The transient behavior of the vapor compression refrigeration cycle is analyzed by considering each component as a “lumped” system, and the resulting sub-models are solved using the Runge Kutta 4th-order method in a MATLAB code at hot and cold ambient temperatures. The time needed to reach steady state temperatures and the temperature values are determined. The maximum required compressor work in the transient phase and at steady state are computed, and as expected, as the ambient temperature increases, both values increase. Finally, the average coefficient of performance (COP) is determined for varying heat transfer coefficient values for the condenser and for the evaporator. The results show that the average COP increases as heat transfer coefficient values for the condenser and the evaporator increase. Starting the system from rest has an adverse effect on the COP due to the higher compressor load needed to change the temperature of the condenser and the evaporator. Finally, the impact on COP is analyzed by redirecting a fraction of the cold exhaust air to provide supplemental cooling of the condenser. It is noted that cooling the condenser improves the system's performance better than cooling the fresh air at 0% of returned air to the system.To sum up, the dissertation shows that the comparison between the conventional reefer and the MC illustrates the promising advantages of the MC, then a transient analysis is developed for deeply understanding the behaviors of the system component parameters, which leads finally to improvements in the system to enhance its performance.

The conversion of H2S enables the recycling of a waste gas into a potential source of hydrogen at a lower thermodynamic energy cost as compared to water splitting. However, studies on the photocatalytic decomposition of H2S focus on traditional deployment of catalyst materials to facilitate this conversion, and operation only when a light source is available. In this study, the efficacy of Direct Ink Written (DIW) luminous structures for H2S conversion has been investigated, with the primary objective of sustaining H2S conversion when a light source has been terminated. Additionally, as a secondary objective, improving light distribution within monoliths for photocatalytic applications is desired. The intrinsic illumination of the 3D printed monoliths developed in this work could serve as an alternative to monolith systems that employ light transmitting fiber optic cables that have been previously proposed to improve light distribution in photocatalytic systems. The results that were obtained demonstrate that H2S favorable adsorbents, a wavelength compatible long afterglow phosphor, and a photocatalyst can form viscoelastic inks that are printable into DIW luminous monolithic contactors. Additionally, rheological, optical and porosity analyses conducted, provide design guidelines for future studies seeking to develop DIW luminous monoliths from compatible catalyst-phosphor pairs. The monoliths that were developed demonstrate not only improved conversion when exposed to light, but more significantly, extended H2S conversion from the afterglow of the monoliths when an external light source was removed. Lastly, considering growing interests in attaining a global circular economy, the techno-economic feasibility of a H2S-CO2 co-utilization plant leveraging hydrogen from H2S photocatalysis as a feed source for a downstream CO2 methanation plant has been assessed. The work provides preliminary information to guide future chemical kinetic design characteristics that are important to strive for if using H2S as a source of hydrogen in a CO2 methanation facility.

Computing the fluid phase interfaces in multiphase flow is a challenging area of research in fluids. The Volume of Fluid andLevel Set methods are a few algorithms that have been developed for reconstructing the multiphase fluid flow interfaces. The thesis work focuses on exploring the ability of neural networks to reconstruct the multiphase fluid flow interfaces using a data-driven approach. The neural network model has liquid volume fraction stencils as an input, and it predicts the radius of the circle as an output of the network which represents a phase interface separating two immiscible fluids inside a fluid domain. The liquid volume fraction stencils are generated for randomly varying circle radii within a 1x1 domain using an open-source VOFI library. These datasets are used to train the neural network. Once the model is trained, the predicted circular phase interface from the neural network output is used to generate back the predicted liquid volume fraction stencils. Error norms values are calculated to assess the error in the neural network model’s predicted liquid volume fraction stencils with the actual liquid volume fraction stencils from the VOFI library. The neural network parameters are optimized by testing them for different hyper-parameters to reduce the error norms. So as to minimize the difference between the predicted and the actual liquid volume fraction stencils and errors in reconstructing the fluid phase interface geometry.

The hydrologic cycle in drylands is complex with large spatiotemporal variationsacross scales and is particularly vulnerable to changes in climate and land cover. To address the challenges posed by hydrologic changes, a synergistic approach that combines numerical models, ground and remotely sensed observations, and data analysis is crucial. This dissertation uses innovative detection and modeling techniques to assess key hydrologic variables in drylands, including irrigated water use, streamflow, and snowpack conditions, answering following research questions that also have broad societal implications: (1) What are the individual and combined effects of future climate and land use change on irrigation water use (IWU) in the Phoenix Metropolitan Area (PMA)?; (2) How can temporal changes in streamflow and the impacts of flash flooding be detected in dryland rivers?; and (3) What are the impacts of rainfall-snow partitioning on future snowpack and streamflow in the Colorado River Basin (CRB)? Firstly, I conducted a scenario modeling using the Variable Infiltration Capacity (VIC) model under future climate and land use change scenarios. Results showed that future IWU will change from -0.5% to +6.8% in the far future (2071-2100) relative to the historical period (1981-2010). Secondly, I employed CubeSat imagery to map streamflow presence in the Hassayampa River of Arizona, finding that the imaging capacity of CubeSats enabled the detection of ephemeral flow events using the surface reflectance of the near-infrared (NIR) band. Results showed that 12% of reaches were classified as intermittent, with the remaining as ephemeral. Finally, I implemented a physically-based rainfall-snow partitioning scheme in the VIC model that estimates snowfall fraction from the wet-bulb temperature using a sigmoid function. The new scheme predicts more significant declines in snowfall (-8 to -11%) and streamflow (-14 to -27%) by the end of the 21st century over the CRB, relative to historical conditions. Overall, this dissertation demonstrates how innovative technologies can enhance the understanding of dryland hydrologic changes and inform decision-making of water resources management. The findings offer important insights for policymakers, water managers, and researchers who seek to ensure water resources sustainability under the effects of climate and land use change.

Advancements to a dual scale Large Eddy Simulation (LES) modeling approach for immiscible turbulent phase interfaces are presented. In the dual scale LES approach, a high resolution auxiliary grid, used to capture a fully resolved interface geometry realization, is linked to an LES grid that solves the filtered Navier-Stokes equations. Exact closure of the sub-filter interface terms is provided by explicitly filtering the fully resolved quantities from the auxiliary grid. Reconstructing a fully resolved velocity field to advance the phase interface requires modeling several sub-filter effects, including shear and accelerational instabilities and phase change. Two sub-filter models were developed to generate these sub-filter hydrodynamic instabilities: an Orr-Sommerfeld model and a Volume-of-Fluid (VoF) vortex sheet method. The Orr-Sommerfeld sub-filter model was found to be incompatible with the dual scale approach, since it is unable to generate interface rollup and a process to separate filtered and sub-filter scales could not be established. A novel VoF vortex sheet method was therefore proposed, since prior vortex methods have demonstrated interface rollup and following the LES methodology, the vortex sheet strength could be decomposed into its filtered and sub-filter components. In the development of the VoF vortex sheet method, it was tested with a variety of classical hydrodynamic instability problems, compared against prior work and linear theory, and verified using Direct Numerical Simulations (DNS). An LES consistent approach to coupling the VoF vortex sheet with the LES filtered equations is presented and compared against DNS. Finally, a sub-filter phase change model is proposed and assessed in the dual scale LES framework with an evaporating interface subjected to decaying homogeneous isotropic turbulence. Results are compared against DNS and the interplay between surface tension forces and evaporation are discussed.