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Atomic-scale simulation of physical and chemical processes during space weathering and planet formation
Title
Atomic-scale simulation of physical and chemical processes during space weathering and planet formation.
Creator
Quadery, Abrar, Schelling, Patrick, Britt, Daniel, Peale, Robert, Kara, Abdelkader, Sohn, Yongho, University of Central Florida
Abstract / Description
We investigate the mechanisms of space weathering and dust grain collisions, two topics of interests from planetary sciences, using atomic-scale simulations. Space weathering is the change in chemical and physical properties of minerals exposed to solar radiation and micrometeorite bombardment on surfaces of airless planetary bodies like the Moon and asteroids. An understanding of the connection between the surface evolution of the minerals and the underlying thermodynamic and kinetic factors...
Show moreWe investigate the mechanisms of space weathering and dust grain collisions, two topics of interests from planetary sciences, using atomic-scale simulations. Space weathering is the change in chemical and physical properties of minerals exposed to solar radiation and micrometeorite bombardment on surfaces of airless planetary bodies like the Moon and asteroids. An understanding of the connection between the surface evolution of the minerals and the underlying thermodynamic and kinetic factors is still missing. We address this issue and determine the time evolution of Frenkel defects in the silicate minerals olivine ((Mg,Fe)$_2$SiO$_4$) and orthopyroxene ((Mg,Fe)SiO$_3$) using molecular dynamics with a pair potential. Defect diffusion and clustering are observed in both the minerals. Cation diffusion occurs more readily in olivine than in orthopyroxene and leads to faster annealing in the former. In orthopyroxene, diffusion of anion defects, especially oxygen interstitials, occurs more rapidly and also exhibits anisotropy, which hinders the annealing process. This difference in defect evolution may explain the experimental observation that surface modifications due to irradiation is more pronounced in orthopyroxene than in olivine. Dust grain collision is the dominant process in the initial stage of planet formation, however, the mechanisms by which dust grains grow to larger aggregates and eventually to kilometer sized planetesimal is still not understood. We explore the role of surface chemistry in energy dissipation and grain adhesion during collision of amorphous silica (SiO$_2$) nanograins using molecular dynamics with a reactive potential, namely ReaxFF. We found nonhydroxylated amorphous silica nanoparticles stick with higher probability than their hydroxylated counterpart. This difference is attributed to the preponderance of unsatisfied dangling bonds on the dry silicate surface which facilitate bond formation during collision, and thereby provide a mechanism for energy dissipation. The speed below which sticking occurs in the dry nanograins is much higher than that found in Earth-based experiments, which suggests any experimental study of dust grain collision should take into account of the chemical environment. We probe into the nanograin collisions further and carry out atomistic simulatons of collisions of molten silica nanograins. We observed in the molten state, amorphous silica is more sticky than it is in the solid phase. This happens due to increased viscoelastic energy dissipation. The result may explain how rocky planets originated from the inner rings of the protoplanetay disks where temperatures were as high as $\sim$ 2000 K. In order to increase the range of materials that could be simulated with ReaxFF potential, and also to examine the different oxidation states of iron associated with nanophase iron formation during space weathering, we made attempt to develop ReaxFF potential for fayalite (Fe$_2$SiO$_4$). We found out fundamental limitations of ReaxFF model to describe three-component minerals. However, during the fitting process we developed a model for iron silicide (FeSi), and made attempt to improve the silica model to obtain better elastic properties. We report here the fitting processes and the observed limitations of ReaxFF model.
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Date Issued
2017
Identifier
CFE0006907, ucf:51691
Format
Document (PDF)
PURL
http://purl.flvc.org/ucf/fd/CFE0006907
Wireless Power Transfer for Space Applications: System Design and Electromagnetic Compatibility Compliance of Radiated Emissions
Title
Wireless Power Transfer for Space Applications: System Design and Electromagnetic Compatibility Compliance of Radiated Emissions.
Creator
Vazquez Ramos, Gabriel, Yuan, Jiann-Shiun, Sundaram, Kalpathy, Wu, Xinzhang, Soto Toro, Felix, University of Central Florida
Abstract / Description
This dissertation evaluates the possibility of wireless power transfer (WPT) systems for space applications, with an emphasis in launch vehicles (rockets). After performing literature review for WPT systems, it was identified that magnetic resonance provides the more suited set of characteristics for this application. Advanced analysis, simulation and testing were performed to magnetic resonance WPT systems to acquire system performance insight. This was accomplished by evaluating/varying...
Show moreThis dissertation evaluates the possibility of wireless power transfer (WPT) systems for space applications, with an emphasis in launch vehicles (rockets). After performing literature review for WPT systems, it was identified that magnetic resonance provides the more suited set of characteristics for this application. Advanced analysis, simulation and testing were performed to magnetic resonance WPT systems to acquire system performance insight. This was accomplished by evaluating/varying coupling configuration, load effects and magnetic element physical characteristics (i.e. wire material, loop radius, etc.). It was identified by analysis, circuit simulation and testing that the best coupling configuration for this application was series-series and series-shunt with Litz wire loop inductors. The main concern identified for the implementation of these systems for space applications was radiated emissions that could potentially generate electromagnetic interference (EMI). To address this EMI concern, we developed the Electromagnetic Compatibility Radiated Emissions Compliance Design Evaluation Approach for WPT Space Systems. This approach systematically allocates key analyses, simulations and tests procedures to predict WPT EMC compliance to NASA's EMC standard Mil-Std-461E/F. Three prototype/magnetic elements were successfully assessed by implementing the WPT EMC design approach. The electric fields intensity generated by the WPT prototypes/magnetic elements tested were: 30.02 dBuV/m, 28.90 dBuV/m and 82.13 dBuV/m (requirement limit: 140 dBuV/m). All three prototypes successfully transferred power wirelessly and successfully met the NASA EMC requirements.
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Date Issued
2012
Identifier
CFE0004448, ucf:49344
Format
Document (PDF)
PURL
http://purl.flvc.org/ucf/fd/CFE0004448
SPRAY COOLING FOR LAND, SEA, AIR AND SPACE BASED APPLICATIONS,A FLUID MANAGEMENT SYSTEM FOR MULTIPLE NOZZLE SPRAY COOLING AND A GUIDE TO HIGH HEAT FLUX HEATER DESIGN
Title
SPRAY COOLING FOR LAND, SEA, AIR AND SPACE BASED APPLICATIONS,A FLUID MANAGEMENT SYSTEM FOR MULTIPLE NOZZLE SPRAY COOLING AND A GUIDE TO HIGH HEAT FLUX HEATER DESIGN.
Creator
Glassman, Brian, Chow, Louis, University of Central Florida
Abstract / Description
This thesis is divided into four distinct chapters all linked by the topic of spray cooling. Chapter one gives a detailed categorization of future and current spray cooling applications, and reviews the major advantages and disadvantages that spray cooling has over other high heat flux cooling techniques. Chapter two outlines the developmental goals of spray cooling, which are to increase the output of a current system and to enable new technologies to be technically feasible. Furthermore,...
Show moreThis thesis is divided into four distinct chapters all linked by the topic of spray cooling. Chapter one gives a detailed categorization of future and current spray cooling applications, and reviews the major advantages and disadvantages that spray cooling has over other high heat flux cooling techniques. Chapter two outlines the developmental goals of spray cooling, which are to increase the output of a current system and to enable new technologies to be technically feasible. Furthermore, this chapter outlines in detail the impact that land, air, sea, and space environments have on the cooling system and what technologies could be enabled in each environment with the aid of spray cooling. In particular, the heat exchanger, condenser and radiator are analyzed in their corresponding environments. Chapter three presents an experimental investigation of a fluid management system for a large area multiple nozzle spray cooler. A fluid management or suction system was used to control the liquid film layer thickness needed for effective heat transfer. An array of sixteen pressure atomized spray nozzles along with an imbedded fluid suction system was constructed. Two surfaces were spray tested one being a clear grooved Plexiglas plate used for visualization and the other being a bottom heated grooved 4.5 x 4.5 cm2 copper plate used to determine the heat flux. The suction system utilized an array of thin copper tubes to extract excess liquid from the cooled surface. Pure water was ejected from two spray nozzle configurations at flow rates of 0.7 L/min to 1 L/min per nozzle. It was found that the fluid management system provided fluid removal efficiencies of 98% with a 4-nozzle array, and 90% with the full 16-nozzle array for the downward spraying orientation. The corresponding heat fluxes for the 16 nozzle configuration were found with and without the aid of the fluid management system. It was found that the fluid management system increased heat fluxes on the average of 30 W/cm2 at similar values of superheat. Unfortunately, the effectiveness of this array at removing heat at full levels of suction is approximately 50% & 40% of a single nozzle at respective 10„aC & 15„aC values of superheat. The heat transfer data more closely resembled convective pooling boiling. Thus, it was concluded that the poor heat transfer was due to flooding occurring which made the heat transfer mechanism mainly forced convective boiling and not spray cooling. Finally, Chapter four gives a detailed guide for the design and construction of a high heat flux heater for experimental uses where accurate measurements of surface temperatures and heat fluxes are extremely important. The heater designs presented allow for different testing applications; however, an emphasis is placed on heaters designed for use with spray cooling.
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Date Issued
2005
Identifier
CFE0000473, ucf:46351
Format
Document (PDF)
PURL
http://purl.flvc.org/ucf/fd/CFE0000473