PhD, University of Cincinnati, 2023, Engineering and Applied Science: Mechanical Engineering

Storage technologies play a significant role in managing temporal fluctuations in energy supply and demand, which is key to transition towards a renewable and sustainable energy infrastructure. Thermal energy storage (TES) systems, in particular, have different applications across numerous industries to improve thermal management, reliability and reduce operation cost. This study focuses on investigating its novel use in enhancing the performance of an air-cooled condenser in thermal power plants. Despite numerous investigations, the large-scale adoption of Phase Change Material (PCM) based TES Systems (which are relatively compact and cost-effective) has been limited due to frequent reports of low PCM reliability, poor TES performance and the lack of relevant experimental data in the literature. This dissertation aims to address such issues to develop and test novel TES designs for high performance and reliability. To select the PCM to be used in the TES, in Chapter 2, the salt hydrate PCM- lithium nitrate trihydrate (Tsf= 30°C, hsf= 274 kJ/kg)- is identified and evaluated by subjecting it to extended thermal cycling to ascertain its long-term performance. Additionally, the material compatibility of the PCM with metals is also evaluated. The results suggest negligible loss of capacity and subcooling indicating the superior performance of the PCM with self-seeding compared to the traditional methods where nucleating agents are used. Additionally, the low thermal conductivity of PCM has typically limited the heat transfer performance in a TES. While a large section of the literature addresses the issue by designing high thermal conductivity PCM composites, the current study looks at a simpler alternative by reducing the length scale of the PCM encasement, thereby avoiding limitations and complications associated with the former method. Experimental and numerical work was carried out to identify the optimal l (open full item for complete abstract)

Committee: Raj Manglik Ph.D. (Committee Chair); Milind Jog Ph.D. (Committee Member); Kishan Bellur Ph.D. (Committee Member); Je-Hyeong Bahk Ph.D. (Committee Member) Subjects: Engineering

Master of Science (M.S.), University of Dayton, 2023, Aerospace Engineering

The main objective of this project is to investigate the performance of Phase Change Materials as the Heat Exchange media in a solar thermal propulsion system. The secondary objective is to visualize and develop the solar thermal propulsion system by running various ground tests using a solar simulator as power source. The project involves design, modelling and fabrication of a bench scale Solar Thermal Propulsion System that can be used to carry and deliver satellites to Moon or Mars' orbit from LEO. PCM's are essential for space travel since the solar energy needs to be stored for the spacecraft to successfully complete the interplanetary missions which consume time and fuel. Without the energy storage system, the spacecraft might need to use conventional fuel ignition systems, which cost money to manufacture and implement in the spacecraft. In this system, the energy from solar light is concentrated into a small cavity through a parabolic reflector and is used to heat the PCM, which in turn heats the propellant and directs it through the nozzle to provide thrust adequate to travel in space. The prototype of the system is first designed using a CAD software and later fabricated into a bench scale model. The model is then set up in the laboratory and connected to a high flux solar simulator. Computational simulations and some test runs of the physical model would be conducted to analyze the performance of PCM in this system

Committee: Rydge Mulford (Committee Chair); Andrew Schrader (Committee Member); Jamie Ervin (Committee Member) Subjects: Aerospace Engineering; Energy; Mechanical Engineering

Doctor of Philosophy, The Ohio State University, 2023, Physics

Nominally metallic systems can be rendered insulating by electronic interactions, disorder, or both, leading to a myriad of interesting many-body phases. In this thesis, we present electronic transport data on a variety of such insulator materials, each with their own unique emergent phenomena. We start with few-layer graphene (FLG), the multilayer counterpart to monolayer graphene, and show that electronic interactions can lead to the development of an electronic energy gap in the band structure near charge neutrality. Previously, this has been associated with spontaneous inversion symmetry breaking, but has only been observed in suspended devices of the highest quality. Here, we show that similar physics can be observed in hexagonal boron nitride-encapsulated devices, alleviating the requirement for suspension. Moreover, in very thick FLG samples, typically thick enough to be considered as three-dimensional graphite, we show the existence of fractional quantum Hall states that are extended through the bulk of the material. Next, we turn to Pt-doped TiSe2, where the interplay between a charge density wave state and a newly discovered quasi one-dimensional insulating state gives rise to ultra slow time-scale physics, along with a strong resistance anisotropy. Finally, transport data as well as angle-resolved photoemission spectroscopy data on Se-doped Ge2Sb2Te5 devices are shown. Here, a disorder-induced metal-to-insulator transition exhibits unique properties, which we attribute to the onset of strong electronic interactions.

Committee: Stuart Raby (Committee Member); Nandini Trivedi (Committee Member); Roland Kawakami (Committee Member); Marc Bockrath (Advisor) Subjects: Physics

Doctor of Philosophy, The Ohio State University, 2023, Electrical and Computer Engineering

This collection of works is an effort toward finding new solutions to challenges in electromagnetic devices, all connected by the implementation of vanadium dioxide (VO2). VO2 is a phase change material (PCM) that exhibits a reversible phase transition at 68 °C between monoclinic insulating and tetragonal conducting states. We designed, simulated, fabricated, and tested various devices in mmWave and optical wavelength domains. As an alternative to complex solid-state switching networks, we chose VO2 for its ability to react to various stimuli as a PCM, low phase transition temperature, and the freedom to design arbitrary geometries for reconfigurable and smart reactive devices. First, we experimented with the growth and characterization of VO2 thin films on sapphire and silicon substrates with Al2O3 buffer layers. Traditionally, VO2 has been deposited on sapphire substrates because of the lattice match between the two. This produces films with high resistivity contrast. However, sapphire is not as versatile a substrate material as silicon, being dielectric rather than semiconductor and extremely difficult to etch. To expand the realm of substrates useful for sputtering high quality VO2, we grew and compared such films on C-plane sapphire and silicon wafers with atomic layer deposited (ALD) alumina (Al2O3) films. Silicon has poor lattice match with VO2, and the alumina eliminates that interface. Furthermore, rapid thermal annealing (RTA) the alumina films before sputtering VO2 provides a basis for quasi-epitaxial films that have similar properties to those on the C-plane sapphire substrates. The figure of merit (FOM) resistivity contrast ratios for these variations are 9.76×104, 3.66×103, and 1.46×104 for C-plane sapphire, as- deposited amorphous ALD alumina on Si, and RTA ALD alumina on Si, respectively. We also characterized the films using X-Ray diffraction, atomic force microscopy, and scanning electron microscopy. In the next step, we examined the material (open full item for complete abstract)

Committee: Nima Ghalichechian (Advisor); Fernando Teixeira (Committee Member); Asimina Kiourti (Committee Co-Chair) Subjects: Electrical Engineering; Electromagnetics; Materials Science; Nanotechnology; Technology

Master of Sciences, Case Western Reserve University, 2022, Physics

The increasing adoption of renewable sources of electricity (i.e. wind and solar farms) is being driven by the demand for carbon neutral electricity production. Although zero carbon is emitted during electricity production, these renewable energy sources suffer from intermittency, which is a mismatch between the supply and demand of electricity of the grid. Renewable energy sources, such as wind and solar, produce their peak electricity at off-demand periods of the day. This strains the electrical grid as it risks over-generation in some locations as well as a need for quick ramping of the electrical load which is hard on electricity producing infrastructure. As a partial solution to intermittency, pumped storage hydropower (PSH) is the dominant form of grid-scale energy storage. PSH accounts for 95% of the U.S. grid-scale storage capacity, which amounts to 22.9 GW of capacity [1]. The EIA also estimates with all possible sites, the U.S. can double their PSH capacity [1]. However, much more than that is not feasible being constrained by the availability of locations suitable for PSH. As a result, other gridscale energy storage options are in development. The main options include batteries, thermal energy storage, compressed air energy storage (CAES) and flywheels. However, these storage options are plagued by high cost per kWh prices, location specificity (ex. PSH, CAES) and/or low energy density. With these concerns in mind, Cratus LLC is developing a molten salt thermal energy storage option known as ThermaBlox, which is location-independent, low-cost, and high-capacity (with the capability to scale). ThermaBlox will play a significant role in intermittency reduction while enabling increased adoption rates of renewable energy.

Committee: Edward Caner (Committee Chair); Dr. Benjamin Monreal (Committee Member); Dr. Robert Brown (Committee Member) Subjects: Chemical Engineering; Energy; Engineering; Entrepreneurship; Fluid Dynamics; Mathematics; Nanotechnology; Physics; Technology

Doctor of Philosophy (Ph.D.), University of Dayton, 2021, Electrical Engineering

Tunable passive rf/microwave devices are the building blocks of reconfigurable electronics. Barium Strontium Titanate (BST) based tunable devices are being studied over for two decades now and this technology is very mature. Researchers have tried different material compositions, substrates, and deposition techniques to increase the tunability of the BST thin films. Researchers have also demonstrated reconfigurable devices at rf/microwave frequencies, however with only limited applications. In this work a novel technique of integrating high tunable dielectric materials such as BST, in combination with a germanium telluride (GeTe) phase change material (PCM) is demonstrated. Integrating phase change material thin films with BST thin films gives additional tuning. The idea of integrating PCM with BST initiates a new era of reconfigurable electronics. These new devices can be implemented with very less fabrication constraints. A low loss rf switch with 0.23 dB insertion loss and more than 19.75 dB isolation at 15 GHz is presented. v An MIM varactor with increased tunability of about 6.3:1 (57%) is achieved, compared to 4:1 tuning of conventional varactor by integration of BST and GeTe thin films. Analog phase shifters with 360° phase shift in the frequency range of 24 GHz to 50 GHz has been demonstrated with good figure of merit (FOM) of 46.64 degrees/dB at 50 GHz and 19.07 degrees/dB at 24 GHz using MIM varactors with BST and GeTe thin films and 319° phase shift at 24 GHz with FOM 12.8 degrees/dB and more than 360° phase shift at 50 GHz with FOM(2V-10V) >21.5 degrees/dB using MIM varactor with only BST thin films. A defected ground structure (DGS) band stop filter with enhanced band-rejection behavior with a notch depth of -39.64 dB @ 27.75 GHz by cascading two-unit cells using BST thin films is achieved. Tunable DGS band stop filters were demonstrated by integration of BST and GeTe with 2.25 GHz tunability from 30.75 GHz to 33 GHz (7.32%) using a single filter a (open full item for complete abstract)

Committee: Dr. Guru Subramanyam (Advisor) Subjects: Electrical Engineering

Master of Science (M.S.), University of Dayton, 2021, Electro-Optics

Material characteristics and crystallinity of germanium antimony telluride (GST) using various design methods for simulation and fabrication are presented. Experimental verification of designs in the mid-infrared are presented for GST-Ag structures and amorphous-crystalline GST structures. Baking an amorphous state GST sample at 200°C for 2 minutes will produce a crystalline state GST which causes the refractive index to increase significantly. Gradually increasing the temperature of an annealed phase change material, such as GST, controls the amount of crystallinity which allows the index of refraction to increase continuously over a significant range. Changing the amorphous state optically allows a lithography-free grating device. The use of GST in these metasurface structures uncovers unique properties that cover transmittance of devices, diffraction orders and tunable optical filters that are angular independent.

Committee: Imad Agha (Committee Chair); Joshua Hendrickson (Committee Member); Shiva Vangala (Committee Member); Swapnajit Chakravarty (Committee Member) Subjects: Design; Electromagnetics; Optics; Physics

MS, University of Cincinnati, 2021, Engineering and Applied Science: Mechanical Engineering

Electric power plants generally operate on the Rankine cycle where the steam from the turbine exhaust is cooled and condensed. A significant amount of water is used as the coolant for the condensation process, and it becomes a challenge where water resources are scarce. Use of air-cooled condensers can help solve the problem. However, the air-cooled condensers can be less efficient in the hottest months of the year and this issue must be addressed to increase their adoption in power plants. One method to overcome this second law limitation is to use an air pre-cooler coupled with a phase change material (PCM) based thermal energy storage (TES) to cool the air supplied to the air-cooled condenser during peak day time temperatures. The TES is recharged at night when ambient air temperature drops below the PCM freezing temperature. In the present study, a computational model is developed to simulate the working of a TES unit coupled with an air pre-cooler using an Eulerian approach. The model was developed using MATLAB and the numerical results are validated against the available experimental data. The energy storage capacities of the two units considered in the study are 100 kJ and 1 MJ. The hot fluid entering the TES unit enables the PCM to undergo melting (extraction). The heat absorbed from the fluid is stored in the PCM and is released during the daytime when the air temperatures are high. The flow direction is switched based on certain conditions and the cold fluid is passed through the opposite direction in the TES unit. This enables the PCM to freeze (charging) and be ready for the next cycle. A parametric study involving the effect of changing PCM melt temperatures and mass flow rates has been carried out for the system. Results show that the PCM melting temperature significantly affects the performance of the TES. A change in the mass flow rate of the heat transfer fluid between the air pre-cooler and the TES can change the melt fraction of the PCM. The comb (open full item for complete abstract)

Committee: Milind Jog Ph.D. (Committee Chair); Raj Manglik Ph.D. (Committee Member); David Thompson Ph.D. (Committee Member) Subjects: Mechanical Engineering

Doctor of Philosophy, The Ohio State University, 2020, Electrical and Computer Engineering

With an increasing demand for high-speed wireless communication, current wire- less infrastructure cannot provide the bandwidth required for high-speed data transfer for multiple users. The next generation of millimeter-wave (mmW) communication systems operate in the frequency range of 30–300 GHz and can provide orders of magnitude greater bandwidth. In addition, these systems rely on adaptive strategies to achieve high data-rate communication which requires reconfigurable elements. In our research, we introduce a new class of reconfigurable radio frequency (RF) microsystems using paraffin phase-change material (PCM) that enables low-loss recon- figuration for mmW components. Paraffin (alkane) is a low-loss nonpolar dielectric that undergoes a 15% reversible volume change through its solid to liquid phase transition. Using this unique combination of loss characteristics and mechanical properties, we have developed continuously variable capacitors. These electro-thermally actuated variable capacitors are low loss with series resistance of less than 0.7 Ω at the mmW band and can be monolithically integrated with antennas and RF components to introduce reconfiguration. In this work, we present a frequency reconfigurable slot antenna which covers the 94 GHz–102 GHz band. In order to achieve reconfiguration, the slot antenna is loaded with two paraffin PCM capacitors. The capacitors are actuated using joule heaters and with the increase in temperature, paraffin goes through a solid to liquid transition. As the volume of the paraffin increases, the capacitance decreases continuously by approximately 15%, which results in increasing the resonance frequency. The realized gain of the antenna at 100 GHz is 3 dBi and it is approximately constant over the reconfiguration range. The Efficiency of the antenna is >72% for the entire reconfiguration range thanks to the low dielectric loss of the paraffin. To evaluate the performance gains of the reconfigurable antennas, new p (open full item for complete abstract)

Committee: Nima Ghalichechian Professor (Advisor); Khalil Waleed Professor (Committee Member); Kubilay Sertel Professor (Committee Member); Kisha Radliff Professor (Committee Member) Subjects: Electrical Engineering; Electromagnetics

Doctor of Philosophy, University of Akron, 2019, Chemical Engineering

Enhancing the thermal conductivity (TC) of polymeric materials for thermal management applications has attracted attentions because of their beneficiary features such as light weight, anti-corrosive, low cost, flexibility and controllable electrical conductivity. Since phonons are the dominant heat carriers in insulating materials, creating pathways for better phonon transfer and decreasing the phonon scattering inside the matrix are the major strategies for TC enhancement. TC of bulk polymers is much less than their single chains because of the chains entanglement that increases the phonon scattering. Therefore, any approaches that decreases the entanglement of chains or enhances their alignment can be used for TC improvement. Traditionally, TC of insulating materials have been enhanced by incorporation of thermally conductive fillers. Formation of a continuous network of these fillers and their alignment can enhance TC even further in the desired direction. The network of fillers can be achieved at high content of fillers that is accompanied with sacrificing other properties such as mechanical properties and results in high cost of final products. As a result, alternative approaches that can form such a network at low content of fillers have attracted attentions. Here, we present three different approaches, which were utilized for TC enhancement of different systems. First, induced co-continuous morphology of an immiscible polymer blend, blend of high density polyethylene (HDPE) and poly (methyl methacrylate) (PMMA) was used for localization of carbon nanofibers (CNFs). The co-continuous morphology of immiscible polymer blends has been previously used for formation of continuous network of electrically conductive fillers and electrical conductivity (EC) enhancement. This method, known as double percolation method, requires both the composition of polymers and fillers reach to percolation threshold above which they form co-continuous phase morphology and continuo (open full item for complete abstract)

Committee: Jiahua Zhu (Advisor); Shiva Sastry (Committee Member); Tianbo Liu (Committee Member); Rajeev Gupta (Committee Member); Qixin Zhou (Committee Member) Subjects: Chemical Engineering; Polymers

MS, University of Cincinnati, 2016, Engineering and Applied Science: Mechanical Engineering

The University of Cincinnati utilizes large scale stratified thermal energy storage (TES) tanks in its water cooling system. The goal of this study is to investigate the potential benefits of an affordable, easily manufactured and installed system incorporating phase change materials (PCM) to augment the thermal capacity of these pre-existing stratified tanks. A 187-gallon laboratory TES tank has been constructed and installed into the chilled water system at the University of Cincinnati's east power plant. A rack made of PVC with cylindrical copper tubes full of PCM placed along its height was set in the center of the laboratory TES tank to test the effects of augmenting the University's TES tanks with PCM. The laboratory TES tank was tested first without the PCM (sensible thermal storage) in order to gather reference data, and then was tested with the cylinders of PCM (sensible and latent thermal storage) augmenting thermal capacity. Separate charge and discharge half-cycle tests were run with flow rates between 0 and 2.5 GPM, and then continuing half-cycle tests were run with a controlled flow rate of 2.5 GPM. Charge time, discharge time, thermocline thickness, storage capacity, half figure of merit (FOM), and system efficiency were calculated for each test and used to draw conclusions on tank performance. It was found that the use of PCM in the laboratory stratified TES tank increased the thermal storage capacity of the tank by approximately 10% while thermocline thickness remained nearly the same, and system efficiency slightly increased.

Committee: Michael Kazmierczak Ph.D. (Committee Chair); Ahmed Elgafy Ph.D. (Committee Member); Milind Jog Ph.D. (Committee Member) Subjects: Engineering

Master of Science (MS), Ohio University, 2014, Mechanical Engineering (Engineering and Technology)

The goal of this study is to evaluate thermally conductive graphite foams for use in thermal energy storage (TES) devices. A phase change material (PCM) can absorb heat during melting and release it during solidification. Most PCM have very low thermal conductivity values, which leads to slow melting rates. Therefore, a thermally conductive enhancer (TCE) is needed to melt the PCM at a faster rate. Graphite foams can be used as a TCE due to their high overall surface area, relatively low weight, and their ability to be manufactured with high thermal conductivity. This thesis examines the melt behavior of the PCM when infiltrated into graphite foam. The heat exchanger coupon used in this study is made of two blocks of foam separated by a parting plate. Two different materials are investigated as the parting plate: stainless steel and aluminum. Two different methods of bonding the foam to the parting plate are evaluated; they are bonding by epoxy, and a brazing method. The melting time of the PCM with different bonding methods are compared to the case when the foam coupons are not bonded to the parting plate. The experimental results indicate that the heat transfer rate is significantly influenced by the bonding method as well the thermal mass associated with the bonding material.

Committee: Khairul Alam (Advisor); David Bayless (Committee Member); John Cotton (Committee Member); Tatiana Savin (Committee Member) Subjects: Mechanical Engineering