Browsing by Author "Schaefer, Laura A"

Now showing 1 - 6 of 6
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    An Investigation into the Stability Limits and Accuracy of the SRT, TRT, and MRT Collision Models in the Lattice Boltzmann Method
    (2018-04-19) Nemer, Mohamed Nazim; Schaefer, Laura A
    Multiphase flow in porous media is found in a variety of engineering problems, including those technologies focused on satisfying the energy needs of an expanding global population whilst minimizing the effects of human activity on climate change. The lattice Boltzmann method (LBM), a kinetics-based method, has displayed potential in simulating multiphase flow in geometrically complex porous media. In this work, the stability and accuracy of three popular collision models within the LBM will be investigated using standard single-phase benchmark tests. In the context of porous media, the permeability of a defined flow will also be determined using the three collision models. Higher stability limits and accuracy are observed for the multiple relaxation time collision model over the two other collision models investigated due to the ability to separately relax the moments corresponding to the problem physics.
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    Lattice Boltzmann Simulations of Blunt and Pointed Geometries
    (2019-11-15) Sun, John; Schaefer, Laura A
    This bio-inspired research will focus on using the lattice Boltzmann method (LBM) to calculate the drag of rigid geometries that resemble a sailfish bill inside a channel with low fluid speed and high viscosity. These 2D simulation results will compare the performance of these similar structures, each with the same area but slightly different shapes, thus shedding light on the aerodynamic properties of the sailfish-bill-like structures in viscous fluids. The LBM model will be established using the open source code on Palabos in C/C++ to create the simulation channel and the obstacle, as well as to capture the fluid behavior on a mesoscopic scale and convert mesoscopic variables to macroscopic ones for data visualization and comparison purposes.
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    Long-term analysis of a small-scale concentrated photovoltaic-thermal system with a nanoparticle-based optical filter
    (2018-04-18) Rodrigues Fernandes, Marcelo; Schaefer, Laura A
    Recent years have seen a sharp increase in the range and implementation of solar energy conversion systems, with an overall goal of reducing fossil fuel dependence. One example of such systems is a concentrated photovoltaic-thermal (CPV-T) system that uses nanofluid-based optical filters, which can generate electricity and absorb heat from sunlight. Although spectral filtering CPV-T systems have been explored in the literature for power generation, they have not been investigated for domestic applications. In this work, dynamic simulations of a small-scale spectral filtering CPV-T system under the climatic conditions of Tucson, Arizona, are performed. The long-term simulations indicate that the proposed CPV-T system can offset a total of 1.317 tons of carbon dioxide (CO2) per year per household. If implemented in 10% of the households in the U.S., the total CO2 offset by the proposed system would be equivalent to the greenhouse gas emissions from 3.19 million passenger vehicles per year.
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    Reduced-order modeling of turbulent plane Couette flow using the Green’s function method and fluctuation-dissipation theorem
    (2020-04-24) Lee, David; Pedram, Pedram; Schaefer, Laura A
    High computational expense prohibits direct numerical simulation of turbulent flows for time-sensitive applications including real-time prediction and control. To address this, reduced-order modeling techniques reduce system dimensionality while maintaining pertinent dynamics. In this thesis, two such techniques---the Green's function method and fluctuation-dissipation theorem---were employed to compute the linear response function of turbulent plane Couette flow at Reynolds numbers of 5,000 and 10,000. Outputs from these methods were validated in both prediction and control applications. The reduced-order models from Green's function method performed well across Reynolds number and problem type, while the model from fluctuation-dissipation theorem performed poorly due to the non-normality of the underlying system. Spectral analysis of the reduced-order model from the Green's function method suggests a previously-unexplored connection with Hankel-dynamic mode decomposition and shows substantial difference in turbulence closure between the Reynolds numbers considered, challenging conventional universal closure models.
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    Simulation of Property Variation in Thermoresponsive Hydrogels
    (2020-04-22) Agbim, Kenechi A; Schaefer, Laura A
    The advancements in the field of smart materials have enabled their use in numerous industries. Though commonly used in biomedical fields, their use in energy management solutions is currently underexplored. Thermoresponsive gels, specifically, have been found to provide cooling to batteries and buildings. Thermal savings in both of these applications often leads to more efficient systems and reduction in energy loads. Similarly, the thermal savings afforded in solar photovoltaic (PV) cell stacks can lead to notable improvements in their performance, thus reducing the energy load to the grid. Many of the current thermal management strategies employed for solar PV systems are less effective due to their size and additional power requirements. Thermoresponsive gels show promise to mitigate the thermal strain often faced by solar PV cells. Their ability to dissipate heat through evaporation is largely driven by their viscoelastic behavior. Much of the research towards understanding the viscoelastic behavior of the low critical solution temperature (LCST) thermoresponsive polymer, poly(N-isopropylacrylamide) (PNIPAAm) has been presented through empirical values that have been found to inadequately match the expected values from the canonical swelling theory. Moreover, as the inclusion of nanomaterials has been found to improve the thermoresponse of the polymer, it is imperative to understand how nanomaterials fundamentally affect the behavior of the polymer in order to influence the design of new smart materials. This work takes a multi-faceted approach to explore how the polymer network varies with temperature and polymer structure. Initially, statistical models are developed to determine the influence selected covariates have on selected viscoelastic outcome predictors. Following this, mesoscale and macroscale tools such as Dissipative Particle Dynamics and semi-empirical analytical modeling respectively, are used to evaluate the changes in the thermal and elastic material properties of the polymer considering variations in monomer chain length, ratios of polymer-to-solvent and nanomaterial-to-polymer. Finally, the feasibility of the pure polymer and nanocomposite materials for use as a passive solar PV cell cooling solution is determined through a comparison of thermal conductivity, specific heat, and coefficient of thermal expansion to those of conventional thermal interface materials.
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    System-scale Analysis of a Parabolic Trough Concentrated Solar Power Plant with Hybrid Thermal Storage
    (2022-07-27) Jean-Louis, Nick; Schaefer, Laura A
    The performance of concentrated solar power plants is dependent on the solar intermittency and seasonal changes to solar irradiation. Commercial application of concentrated solar power plants currently incorporates sensible and latent heat storage, both of which lack long term storage viability. Thermochemical energy storage (TCES) is proposed as a solution for long-term storage, dehydrating/storing during summer months and hydrating/releasing during the winter. TCES is considered as a parallel component to a two-tank indirect molten salt storage covering solar intermittency. The TCES is also in series with a secondary two-tank indirect molten salt storage which operates at a lower temperature, reducing the heat transfer fluid (HTF) exit temperature to the solar field inlet temperature during charging, or to increase the HTF exit temperature to the steam train entrance temperature during discharging. The SEGS VI solar field and power generation parameters are used to model a 5 MWe capacity plant. The TCES is also modeled with and without a porous channel decreasing dehydration time by 54%. Results present three storage sizes of 8, 12, and 16 hours, covering the distribution of energy during operation. Outputs are analyzed based on their monthly averages favoring 16 hour storage to minimize reactor hydration during the summer. Configurations which further benefit the CSPP + TCES combination are also discussed.