MS, University of Cincinnati, 2022, Engineering and Applied Science: Mechanical Engineering

Understanding the mechanism of bubble nucleation and growth is critical for optimizing the boiling heat transfer process. The microlayer region formed under the bubble departure is known to be a major contributor to phase change heat transfer but its evolution, spatio-temporal stability, and impact on macroscale bubble dynamics are still relatively unknown. In the thin film microlayer region, the vapor pressure is balanced by a combination of capillary, disjoining, and liquid pressures. Thermally driven evaporation in the curved thin film is suppressed by disjoining pressure at the nanoscale leading to a peak in evaporation flux in the microlayer region. Using a lubrication approximation coupled with conservation laws and the augmented Young-Laplace equation, 3rd order nonlinear film evolution equation is obtained. The evolution equation is solved numerically using the ODE 45 method in MATLAB. A variable wall temperature boundary condition is employed at the solid-liquid interface and is balanced by evaporative heat loss at the liquid-vapor interface. Contrary to most models, the solution begins in the thicker region of the film and proceeds in the direction of reducing film thickness. The solution method is devoid of tuning parameters or guessed inputs. Experimentally measured film thickness and its derivatives are used as inputs in the thicker region and the model is evaluated to obtain a film profile down to the nanoscale and a corresponding local evaporative flux. The modeling results compare favorably with spatio-temporal experimental measurements of the microlayer. By comparing the film profiles at multiple time steps, the accommodation coefficient could be estimated and its influence on the evaporative flux distribution is discussed.

Committee: Kishan Bellur Ph.D. (Committee Member); Raj Manglik Ph.D. (Committee Member); Milind Jog Ph.D. (Committee Member) Subjects: Mechanical Engineering

MS, University of Cincinnati, 2024, Engineering and Applied Science: Aerospace Engineering

Liquid-vapor phase change is a key to modeling countless multiphase flows, notably in the storage of cryogenic propellants during long-term space missions. Although recent studies have progressed our understanding of the physics of phase change, reliable models to compute the interphase mass transfer remain elusive, and popular phase change models rely heavily on tuning coefficients to model the phase change mass transfer. Large inconsistencies in the phase change calculations occur due to the unpredictable nature of these tuning coefficients. In this work, several pieces of the kinetic phase change mechanism are used from other studies to build a new computational routine capable of modeling kinetic phase change without the need for tuning parameters. A common problem with implementing kinetic phase change models is the need for values of the accommodation coefficient. This problem is solved by using a transition state theory-based model to compute the accommodation coefficient as a function of the liquid and vapor densities. Vapor temperature is found to play a critical role in the accurate prediction of phase change rates. Errors as large as one order of magnitude are seen for deviations as small as 0.1% in the values of the vapor temperature. Accurate modeling of phase change rates requires vapor temperature within the Knudsen layer to be used as inputs to the kinetic models. Due to the inability of macro-scale computational fluid dynamics (CFD) models to capture temperature gradients in the Knudsen layer, a new parameter, γ, is introduced to approximate the Knudsen layer vapor temperature. This new computational routine is implemented within Ansys Fluent™ with the help of User-Defined Functions (UDFs). CFD simulations are used to recreate phase change experiments from recent studies involving Hydrogen and Methane. Data from the CFD simulations are used to correlate γ to the evaporation rate. A function to calculate γ using the area-averaged phase change molar f (open full item for complete abstract)

Committee: Kishan Bellur Ph.D. (Committee Chair); Prashant Khare Ph.D. (Committee Member); Shaaban Abdallah Ph.D. (Committee Member) Subjects: Fluid Dynamics

Master of Science in Mechanical Engineering, Cleveland State University, 2023, Washkewicz College of Engineering

Most of the rain that falls over land, falls over forests, which cover approximately one-third of global land surface. Significant immediate and wide-ranging impacts are exerted on hydrological, ecological, and societal systems due to canopy-rainfall interactions, altering rainwater supply to the surface. All storm-related hydrological processes are impacted by the relative rates that canopy surfaces retain, evaporate, and redistribute rain. Many forest canopies host a community of plants called epiphytes that are generally capable of storing and evaporating substantial water. Epiphytes are comparatively under-researched regarding their role in rainfall partitioning compared to bark and leaves. Skidaway Island in Savannah, Georgia, has a forest canopy that hosts an epiphyte community consisting primarily of these three groups on a single host tree species, Quercus virginiana (southern live oak). The objective of this research was to determine the amount of time the study epiphytes were saturated, the amount of rainfall evaporated by the epiphytes, and the amount of condensation received by the epiphytes. It was found that saturation time had a positive relationship with Pleopeltis and detritus biomass, and decreased with Tillandsia. An indirect positive relationship between Pleopeltis and detritus biomass with evaporation and condensation amounts was observed.

Committee: John Van Stan (Advisor); Yong Tao (Committee Chair); Michael Gallagher (Committee Member) Subjects: Environmental Science; Mechanical Engineering

Doctor of Philosophy, The Ohio State University, 2022, Mechanical Engineering

Evaporation of fuel droplets and mixing of fuel vapor with the oxidizer is the driving force for combustion reactions in many combustion devices. Since the flow in most practical combustion devices is turbulent, an understanding of the interactions among turbulence, mixing and reactions is necessary to improve fuel efficiency and reduce pollutant emissions. However, the effects of small-scale turbulence on the dynamics of evaporation and the resultant fuel vapor field are relatively less known. Fluctuating relative velocity and inhomogeneities in the fuel vapor field around the droplets have been observed to affect the droplet vaporization rates. Apart from the droplet-turbulence interactions, droplet-droplet interactions and turbulent mixing of the fuel vapor with the oxidizer are other aspects critical to the formation of a combustible mixture. The present work aims to contribute towards a physical understanding of the droplet-turbulence and droplet-droplet interactions as well as the turbulent mixing of fuel vapor by performing droplet-resolved direct numerical simulation (DNS). The effects of turbulence on the evaporation of droplets larger than the Kolmogorov length scale are investigated using droplet-resolved DNS. The DNS is performed using a numerical method based on the immersed boundary method (IBM) that is developed here to perform efficient DNS with multiple droplets. Firstly, an improved IBM for a general particulate flow is developed. The displaced forcing and the predictor-corrector forcing are proposed and validated for the prediction of drag and scalar gradients on the immersed body in incompressible flows. The method is extended for application to variable density flows using a low Mach formulation by carefully considering the phase change. The predictions of evaporation rates are validated by comparison with a correlation based on experimental data for both stationary and moving droplets. The droplet-resolved DNS considers droplets (open full item for complete abstract)

Committee: Seung Hyun Kim (Advisor); Jeffrey Sutton (Committee Member); Sandip Mazumder (Committee Member); Datta Gaitonde (Committee Member) Subjects: Aerospace Engineering; Mechanical Engineering

PhD, University of Cincinnati, 2022, Engineering and Applied Science: Aerospace Engineering

The injection of a liquid jet into a subsonic crossflow (LJCF) is a common strategy for atomizing liquid fuels in a wide variety of propulsion system applications. This has led to significant research interest in characterizing the complex multiphase and unsteady flowfield of the LJCF. The majority of previous research has focused on the injection of various liquids into ambient temperature and pressure air crossflows. However, modern high performance propulsion systems operate at increasingly elevated temperatures and pressures which can have unique implications for LJCF behavior. Additionally, if liquid fuel is circulated to cool propulsion system components prior to injection, the impact of elevated fuel temperatures on LJCF atomization and evaporation becomes important. The few studies that have investigated the LJCF at elevated jet and crossflow temperatures have avoided conditions where droplet evaporation becomes an important factor while also using test liquids that are not relevant to propulsion systems, such as water. The current work seeks to fill this void in the available literature by experimentally investigating the impact of elevated liquid jet and crossflow temperatures on the features of the LJCF in a well characterized test environment. Significant effort was put forth to characterize both the state of crossflow upstream of the injector, and the flow leaving the injector at different test conditions. Emphasis was placed on extracting quantitative data and developing empirical correlations that describe both the near- and far-field characteristics of the LJCF. This was done with the intent to provide validation data for numerical simulations of the LJCF. Characterization of the crossflow upstream of injector included measurements of the inlet gas temperature and Mach number profiles, the injection wall boundary layer, preburner emissions, and local test section acoustics. Injector evaluation consisted of internal injector visualizatio (open full item for complete abstract)

Committee: Ephraim Gutmark Ph.D. (Committee Member); Rodrigo Villalva Gomez Ph.D. (Committee Member); Prashant Khare Ph.D. (Committee Member); Shaaban Abdallah Ph.D. (Committee Member) Subjects: Aerospace Materials

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

Macroscopic assembly of graphene into 2D films or paper is a new form of graphene which utilizes its exceptional properties. In this effort several fabrication processes of graphene-based paper were studied, and the mechanisms of thermal management and deicing were investigated. The details of these techniques were studied and their effect on the structure, quality, and in-plane thermal conductivity of graphene-based paper was evaluated. The techniques used to prepare graphene-based paper were chemical vapor deposition (CVD), hot pressing of graphene slurry, and evaporation induced self-assembly (EISA). The thermal and electrical conductivities of the resulting papers were measured, and various structural characterizations were made, including scanning electron microscopy (SEM), Raman spectroscopy, X- ray diffraction (XRD), small angle X-ray scattering (SAXS), and optical microscopy. SEM images showed the morphology of graphene-based paper made by the different techniques. XRD patterns had a sharp peak at 26.5° to show that the matching of crystallinity for graphene paper prepared via different techniques. SAXS patterns showed high directionality for CVD graphene-based paper. In-plane thermal conductivity measurement was performed using custom-built steady state in-plane thermal conductivity device. According to the measurements of in-plane thermal conductivity, CVD graphene-based paper has highest thermal conductivity than hot pressing and EISA techniques because of long phonon mean path, absence of defects and highly orientation of CVD graphene-based paper. This was important because heat spreaders made from high thermal conductivity materials are one of the most effective techniques used to dissipate heat generated in microelectronic devices, thereby enhancing the performance and reliability of electronics. A graphene-based paper composite panel was fabricated using a wet layup / vacuum bagging technique to study the mechanism of graphene-based paper for deic (open full item for complete abstract)

Committee: Khalid Lafdi (Advisor); Youssef Raffoul (Committee Member); Erick Vasquez (Committee Member); Donald Klosterman (Committee Member) Subjects: Materials Science

Doctor of Philosophy, Case Western Reserve University, 2021, Chemical Engineering

Many aspects of electrostatics remain poorly understood, especially in regards to how liquids and gases effect surface charge. We discovered a previously unknown phenomenon where a solvent evaporating off of a surface in an electric field leaves behind an electrostatic charge. Our experiments determined that this charge was first inducted into the liquid film before being trapped on the surface after the liquid evaporates. Using Kelvin Force Microscopy (KFM) and an interdigitated electrode (IDE), we were able to recreate the experiment on the microscopic scale. We were able to use the “evaporation charging” effect to create bipolar charge mosaics, where the surface charge varies by magnitude and polarity in a distance of microns. Additionally, we tested how gas phase ions can discharge a surface through the use of a levitating charged sample. By measuring the change in the sample's electrostatic potential, we were able to determine the rate of charge decay due solely to gas phase ions. Using our experimental data, we developed a model that accounts for this decay by considering how the geometry of the charged surface creates an electric field in a volume of air that ions can be drawn from. The results of all of these experiments show that liquids and gases play a larger-than-expected role in electrostatics and the failure to fully comprehend their effects may account for why so many electrostatic experiments are difficult to reproduce.

Committee: Daniel Lacks (Advisor); Mohan Sankaran (Advisor); Martin Heidi (Committee Member); Zorman Christopher (Committee Member) Subjects: Chemical Engineering; Electrical Engineering; Engineering

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

This dissertation proposes a systematic methodology for monitoring the Evaporative Emissions Control (EVAP) System after an key-off event before the next key-on. To achieve the monitor, studies of physical processes that occur in the system and collection of extensive experimental data are carried out. The proposed EVAP system monitor leverages information from the physics-based evaporation model and the strengths of data-driven machine learning techniques to detect small leaks and to predict gasoline vapor mass adsorption in the canister after engine-off. Contributions of this dissertation include first constructing a physics-based gasoline evaporation model in which equilibrium vapor pressure is estimated by gasoline composition and physical properties of the constituents. The model is validated with experimental data. The second contribution is the design and collection of experiments covering a broad range of system operations. Detailed preparation procedures are created for a small-scale tank in an environmental chamber, a production tank on a test bench, and a full EVAP system on a test vehicle, to analyze gasoline evaporation and adsorption activities. Lastly, an EVAP system monitor methodology using physics-based knowledge as well as data-based machine learning methods is designed developed and implemented. This is the first such monitoring methodology applied to an automotive evaporative emissions control system. The performance of the novel EVAP system monitor is demonstrated on experimental data collected from a test vehicle, showing substantially higher diagnostic and predictive accuracy than existing methods.

Committee: Giorgio Rizzoni (Advisor); Abhishek Gupta (Committee Member); Yingbin Liang (Committee Member); James Daley (Committee Member); Douglas Alsdorf (Other) Subjects: Automotive Engineering; Electrical Engineering; Mechanical Engineering

Master of Science, The Ohio State University, 2019, Food Science and Technology

Clostridioides difficle infection (CDI) is the most common health-care associated infection in the United States. Annually, CDI infects nearly half a million patients, kills 29,000 and costs the healthcare system an estimated US$6.3 billion. Although this pathogen can be treated with antibiotics, in 25% of cases, the bacterium does not respond to antibiotics and the patient develops a recurrent infection. Due to the hardy nature of the bacteria causing the recurrent CDI, additional, more costly treatment methods such as fecal microbiota transplantation must be employed. Alternatively, consumption of kefir, a commercially available fermented dairy beverage with live probiotic cultures, was recently found to be effective in curing recurrent CDI when consumed alongside the prescribed antibiotic treatment. Unfortunately, kefir has limited patient acceptance due to its strong acidic and fruity flavors resulting from the fermentation process. To combat this, kefir may be further processed using freeze-drying or vacuum evaporation to remove undesirable volatile organic compounds (VOCs) that greatly contribute to flavor, but heat during processing must be minimized to avoid reducing the population of beneficial microorganisms. In this study, effect of vacuum evaporation and freeze-drying on kefir VOC concentration, microbial viability and activity, and sensory quality was assessed. Commercially manufactured kefir was subjected to either a vacuum evaporation or freeze-drying treatment, or was not further processed (control). Loss of volatile compounds was monitored at the ppb level using selected-ion flow-tube mass spectrometry (SIFT-MS); kefir acceptability was evaluated by untrained panelists using a 9-point hedonic scale, and differences among treatments was determined by comparing mean scores; microbial viability was assessed using selective media for enumeration of Lactobacillus spp. and Lactococcus spp.; and microbial activity was assessed by meas (open full item for complete abstract)

Committee: Valente B. Alvarez PhD (Advisor); Rafael Jimenez-Flores PhD (Committee Member); Ahmed Yousef PhD (Committee Member) Subjects: Food Science

Master of Science, University of Akron, 2018, Mechanical Engineering

Due to the need for a drastic increase of the data storage density of hard disk drives, the heat-assisted magnetic recording (HAMR) technology was developed to write data to the disk at a significantly elevated temperature such that the coercivity of the magnetic medium could be lowered for easy data-writing while maintaining the magnetization patterns for years without suffering thermal instability. Previous studies were based on a Gaussian temperature distribution with axisymmetry for simplicity. However, because of the fast disk rotation, the temperature distribution on the disk surface under laser illumination tends to deviate significantly from the axisymmetric distribution that is typical for a slow-moving solid body. The temperature distribution can exhibit a tail in a trailing region, as confirmed by a previous finite element analysis. In this study, an approximation scheme for the temperature distribution over and near the thermal spot of the laser beam containing a tail was proposed based on the weighted sum of stationary and fast-moving heat source solutions. This approximation not only significantly reduced the computation time for solving the current problem but also represents a novel and efficient method in tribology for approximating the temperature distribution due to heating for the whole range of speeds and thermal-spot sizes. By using this approximated temperature distribution, a governing partial differential equation for the nanoscale lubricant film was solved numerically by considering the evaporation rate, surface tension, disjoining pressure and thin-film enhanced effective viscosity. The results for the perfluoropolyether lubricant reveal the process of formation of a lubricant trough: an indent of the lubricant profile first forms and grows to a steady-state depth, followed by a continuous extension at the rate of the disk velocity. Based on the comparisons of solutions obtained with and without evaporation, both evaporation and thermal ca (open full item for complete abstract)

Committee: Shao Wang Dr. (Advisor) Subjects: Mechanical Engineering

Master of Science, The Ohio State University, 2018, Civil Engineering

Eddy covariance measurements of evaporation and carbon dioxide flux in coastal systems are an important tool to understand ecological and biophysical properties of ecosystems such as coastal reefs. However, few studies have examined mass fluxes under highly contrasting air-sea temperature conditions, such as those found in the Red Sea or any other desert-surrounded seas and coastal areas. This study analyses season-long observations of evaporation and carbon flux at the Gulf of Aqaba coast, northern Red Sea. Data were collected using the eddy-covariance method with a two-tower setup to measure evaporation rates over land and sea and the advection between them. Using a 3D mass balance approach, total evaporation was calculated as the sum of two main components in our site: horizontal advection and turbulent vertical flux, with half-hourly change of water vapor storage and horizontal flux divergence found to be negligible. Average evaporation rates were 11.4 [mm day-1] from April through May (early summer), and 10.5 [mm day-1] from June through August (summer). These rates of evaporation near the shore were considerably higher than values reported in other studies typically used to represent the mean for the whole Gulf area. The results of this study show that evaporation rates computed by common bulk models approximate the mean values of evaporation but have poor representativeness of the intra-daily temporal variation of evaporation. The coastal reef was a CO2 sink over the period of measurements, significantly higher in June through August than in April through May. The main environmental drivers of CO2 flux were humidity, water temperature, sensible heat flux and wind speed. There was a significant correlation between CO2 flux and evaporation attributed to common environmental drivers of gas diffusion, turbulent fluxes, and horizontal transport. Measurements of mass fluxes in coastal waters need to use at least a two-tower system to account for the effect of horiz (open full item for complete abstract)

Committee: Gil Bohrer (Advisor); Jeffrey Bielicki (Committee Member); May Andrew (Committee Member) Subjects: Environmental Engineering; Meteorology

Master of Science, The Ohio State University, 2018, Materials Science and Engineering

Atom probe tomography (APT) produces 3D, atom-by-atom images of a sample microstructure that provide impressive detail of materials systems. With advancements in detector and laser technology in the last couple decades, APT has gained new life and has established itself as a premier technique in materials characterization. New laser technology has allowed for data collection rates of 100M atoms/hour or more while new detector technology has pushed detection rates up to and beyond 80%. The technique holds huge promise for providing a direct link between the actual atomic microstructure of a material and its properties. Being a destructive technique by nature, and ultimately relying on observing the surface of the sample, the atom probe suffers from artifacts in data that are sometimes not apparent. Reconstruction algorithms, too, have been hampered in adapting to these artifacts, as for many of them the mechanisms are simply not known. Development of physically complete, accurate forward simulations of the field evaporation process can provide both the mechanistic information and a testing framework necessary for future advances in reconstruction algorithms. The work presented in this thesis is focused on expanding the capabilities of current atom probe simulations though application of both DFT and classical atomistic modeling techniques. Chapters 1-3 describe the theoretical underpinnings along with the details of the DFT calculations and atom probe simulation codes used in this research. Three projects focused on creating a more physically detailed model for simulation of atom probe are presented. Chapters 4 and 5 present work done developing a model for the site specific evaporation field of pure FCC emitters. This site specific model is parametrized in terms of the neighbor counts of an evaporated surface atom in order to more closely match the real evaporation sequence. In chapter 4, it is shown that this modified evaporation sequence is the origin of the (open full item for complete abstract)

Committee: Wolfgang Windl Ph.D. (Advisor); Maryam Ghasisaeidi Ph.D. (Committee Member) Subjects: Materials Science

Master of Science (MS), Ohio University, 2017, Mechanical Engineering (Engineering and Technology)

Evaporation of water in hydrophobic confinement has been a subject of numerous studies because of its key role in functioning and self-assembly of many biologically relevant systems, such as protein folding, formation of lipid bilayers, operation of ion channels, etc. Evaporation is an activated process and hence is a rare event in molecular time-scales. There is no consensus on a continuum thermodynamic theory which captures different aspects of the process satisfactorily. We study the simple case of evaporation of water confined between two rigid hydrophobic walls of tunable hydrophobicity, and adopt nucleation theory as our continuum thermodynamic approximation. We propose analytical expressions for free energy barrier and size of the critical vapor tube necessary for evaporation to occur. In the theory, we incorporate the effect of line tension, that has been neglected so far. To validate the expressions and explore role of line tension, we obtain free energy barriers and critical radii to evaporation from molecular simulations, by employing Indirect Umbrella Sampling (INDUS) and committor probability analysis methods. By comparing the results from simulations and theory, we find that the role of line tension is crucial in evaporation of water in hydrophobic confinement.

Committee: Sumit Sharma Dr. (Advisor); Horacio Castillo Dr. (Committee Member); Sarah Hormozi Dr. (Committee Member); Keerti Kappagantula Dr. (Committee Member) Subjects: Chemical Engineering

Doctor of Philosophy, The Ohio State University, 2017, Electrical and Computer Engineering

Variations in the refractive properties of the marine atmospheric boundary layer (MABL) can lead to non-standard propagation of radiowaves. An ability to quickly assess the influence of the atmosphere on shipboard surveillance and communication systems is required to avoid unwanted extended signal transmissions as well as poor functionality of these systems. While refractive conditions can be determined in numerous ways, methods utilizing radio frequency propagation measurements can directly determine the impact of the atmosphere on these systems. A novel transmit-receive array system called the X-band Beacon-Receiver array (XBBR) was developed with the purpose of determining MABL evaporation duct height (EDH) values. An experiment campaign was conducted to deploy the multichannel array system and corresponding beacon transmitters to investigate their ability to characterize MABL refractivity utilizing both the amplitude and phase of recorded signals. The method proposed compares propagation loss and phase values given by the Variable Terrain Radio Parabolic Equation (VTRPE, Ryan, 1991) modeling software for various propagation environments with measurements obtained by the XBBR array. Meteorological data was also recorded to act as input to the Navy Atmospheric Vertical Surface Layer Model (NAVSLaM); this allows for determination of the evaporation duct height from in-situ meteorological data to serve as the ground truth for comparison with our evaporation duct height estimation. Furthermore, this dissertation investigates the temporal and spatial fluctuations of radio frequency transmissions in a turbulent atmosphere. The multiple receive channels of the XBBR allow for the covariance of signals measured at each receiver to be compared with a model and atmospheric turbulence parameters to be extracted. This model is then used to simulate possible transmit and receive array configurations in an attempt to optimize system performance and minimize ambiguities (open full item for complete abstract)

Committee: Joel Johnson (Advisor); Fernando Teixeira (Committee Member); Robert Burkholder (Committee Member) Subjects: Electrical Engineering

Doctor of Philosophy, University of Toledo, 2017, Physics

Spectroscopic ellipsometry (SE) is a powerful tool to characterize multilayered thin films, providing structural parameters and materials optical properties over a wide spectral range. Further analyses of these optical properties can provide additional information of interest on the physical and chemical properties of materials. In-situ real time SE (RTSE) combines high surface sensitivity with fast data acquisition and non-destructive probing, thus lends insights into the dynamics of film growth. In this dissertation, the methods of SE have been applied to investigate the growth and properties of material components used in the CIGS thin film photovoltaic technology. Examples of RTSE data collection and analyses are demonstrated for the growth of selenium (Se), molybdenum diselenide (MoSe2) and copper selenide (Cu2-xSe), used in CIGS technology which can then be applied in complete analysis of three-stage CIGS deposition by co-evaporation. Thin film Mo deposited by sputtering is the most widely used back contact for solar cells using CIGS absorbers. In this study, in-situ and real time characterization have been utilized in order to investigate the growth as well as the structural, optical, and electronic properties of Mo thin films deposited by DC magnetron sputtering at different substrate temperatures. In these studies, the surface roughness on the Mo is observed to decrease with increasing substrate temperature. The growth rate, nucleation behavior, evolution of surface roughness and development of void structures in Mo show strong variations with deposition temperature. In depth analyses of (e1, e2) provide consistent estimates of void fraction, excited carrier mean free path, group speeds of excited carriers and intrinsic stress in the films. Complementary ex-situ characterization of the as deposited Mo films included XRD, resistivity measurements by four-point-probe, SEM, and profilometry. This dissertation describes the research performed on the (In (open full item for complete abstract)

Committee: Robert Collins (Committee Chair); Nikolas J. Podraza (Committee Member); Bo Gao (Committee Member); Jacques G. Amar (Committee Member); Dean M. Giolando (Committee Member) Subjects: Materials Science; Physics; Solid State Physics

Doctor of Philosophy, The Ohio State University, 1974, Graduate School

Committee: Not Provided (Other) Subjects: Engineering

Doctor of Philosophy, The Ohio State University, 1969, Graduate School

Committee: Not Provided (Other) Subjects: Agriculture

Doctor of Philosophy, The Ohio State University, 2016, Physics

Several advancements in our understanding of fuzzball black have been made via the study of a dual Conformal Field Theory. In this approach, the full picture of black hole formation and eventual evaporation is expected to correspond to thermalization in the CFT dual. In other words, an initial set of high-energy wavepackets that 'break up' into a large quantity of low-energy excitations in the CFT should be the dual to an initial set of high-energy infalling particles forming a black hole that then evaporates via a large quantity of low-energy Hawking radiation in the gravity description. The nature of a fuzzball's CFT dual depends on particular parameters of the underlying gravity theory, its moduli space, and it is conjectured that some choice of parameters is dual to a particularly simple `orbifold' CFT. Calculations at this orbifold point match some semi-classical results, but it is also clear that the orbifold point is does not exactly match the behavior of gravity as we know it. It is thus necessary to move away from this orbifild point via the perturbative application of a deformation operator. A framework for studying deformations away from the orbifold point was developed some time ago, but its application was previously limited to the simplest of tree-level processes. My work extends this framework to all tree-level processes. At this stage, there is no clear indication of thermalization. In addition, analysis is muddied by a change in the Hilbert space of the CFT. This makes comparisons between initial and final states difficult to perform. To address this, the framework was further extended to include a simple one-loop process. This process maintains a consistent Hilbert space between in and out states, allowing a more straightforward search for thermalization effects. Furthermore, certain patterns occurred when comparing the one-loop results to the tree-level process that constitutes the loop's first half. It is thus natural to co (open full item for complete abstract)

Committee: Samir Mathur (Advisor); Junko Shigemitsu (Committee Member); Amy Connolly (Committee Member); Andrew Heckler (Committee Member) Subjects: Physics

MS, University of Cincinnati, 2014, Engineering and Applied Science: Mechanical Engineering

In present study, the enhancement of meniscus evaporation by changing meniscus shape and area was investigated. Rather than observing the meniscus shape directly, an alternative method has been utilized. A Condensation Particle Counter (CPC) structure, which benefits from meniscus evaporation of a porous media to make vapor for water droplet growth, has been introduced to analyze the production water droplet. By analyzing the size and concentration of the condensed water droplet from CPC, the enhancement of meniscus evaporation taken place at the porous media was determined. The meniscus shape and area alterations were controlled by applying an additional pressure onto the meniscus. The results of the bigger condensed water droplet and higher concentration clearly demonstrate that the enhancement has been achieved to the meniscus evaporation, which was led by changing of the additional pressure applied to the meniscus of the porous media.

Committee: Sang Young Son Ph.D. (Committee Chair); Pramod Kulkarni D.Sc. (Committee Member); Frank Gerner Ph.D. (Committee Member) Subjects: Mechanics

Doctor of Philosophy, Case Western Reserve University, 2014, EMC - Aerospace Engineering

The enabling of all future in-space cryogenic engines and cryogenic fuel depots for future manned and robotic space exploration missions begins with technology development of advanced cryogenic fluid management systems upstream in the propellant tank. Gravity affects many fluidic processes, such as the separation of the liquid and vapor phases within the propellant tank. By design, all in-space cryogenic engines and cryogenic fuel depots require vapor free liquid delivery. To meet these fluid transfer requirements over a wide range of mission flow rates, gravitational and thermal environments, propellant management devices will be required to favorably position liquid and vapor within the tank. The purpose of this work is to develop such robust and flexible liquid acquisition devices (LAD), particularly for low surface tension cryogenic propellants operating in microgravity environments, through a battery of component level and full scale ground experiments, and development of analytical tools. Models are first developed from first principles for the influential factors which govern LAD performance, which include bubble point pressure, flow-through-screen pressure drop, wicking rate, and screen compliance. The literature is rigorously reviewed to gather data to validate the models. Then a series of parametric component level tests are conducted in room temperature liquids and cryogenic hydrogen, nitrogen, oxygen, and methane to determine the effect of varying screen type, liquid, liquid temperature and pressure, and pressurant gas type and temperature on the bubble point pressure. LAD channels are then constructed, and full scale LAD outflow tests are conducted in liquid hydrogen to simulate fluid transfer from a propellant tank in a variable thermal environment, to determine pressure drop contributions, and to assess reliability of the LADs at cryogenic temperatures. One of the channels is thermally flight representative with a custom designed internal heat excha (open full item for complete abstract)

Committee: Yasuhiro Kamotani (Committee Chair); Jaikrishnan Kadambi (Committee Member); Jay Adin Mann Jr. (Committee Member); David Chato (Committee Member) Subjects: Aerospace Engineering; Alternative Energy; Chemical Engineering; Chemistry; Engineering; Experiments; Fluid Dynamics; Low Temperature Physics; Mathematics; Mechanical Engineering; Physics