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Numerical Modeling Of High Temperature Shell And Tube Heat Exchanger And Chemical Decomposer For Hydrogen Production, Gayatri Kuchi
Numerical Modeling Of High Temperature Shell And Tube Heat Exchanger And Chemical Decomposer For Hydrogen Production, Gayatri Kuchi
UNLV Retrospective Theses & Dissertations
This thesis deals with the development of a three-dimensional numerical model of high temperature shell and tube heat exchanger and chemical decomposer to examine the percentage decomposition of a sulfur trioxide gaseous mixture for the production of hydrogen by the sulfur-iodine thermochemical water splitting cycle, a candidate cycle in the U.S. Department of Energy Nuclear Hydrogen Initiative. A counter flow type straight tube shell and heat exchanger concept is chosen for the analysis. The reacting fluid is a mixture of sulfur trioxide gas and water vapor inside the tubes of the heat exchanger and high temperature helium is the gas …
Optimization Of Bipolar Plate Design For Flow And Temperature Distributions Using Numerical Techniques, Kiran Mohan Veepuri
Optimization Of Bipolar Plate Design For Flow And Temperature Distributions Using Numerical Techniques, Kiran Mohan Veepuri
UNLV Retrospective Theses & Dissertations
Although water is fed controllably into the flow channels in the bipolar plates surrounding the membrane electrode assembly (MEA), the complex flow geometry can lead to non-uniformity of the flow and temperature distribution inside the channels. In addition, non-uniform temperature distribution in the cell will affect the electrochemical process for hydrogen production or fuel cell applications. There are many studies on the theoretical analysis of fuel cells, but not many have been reported on the characteristics of the PEM electrolyzer; In this thesis work, numerical simulations were carried out on the basic bipolar plate given by the Proton Energy Systems …
Numerical Study Of High Temperature Bayonet Heat Exchanger And Decomposer For Hydrogen Production, Vijaisri Nagarajan
Numerical Study Of High Temperature Bayonet Heat Exchanger And Decomposer For Hydrogen Production, Vijaisri Nagarajan
UNLV Retrospective Theses & Dissertations
This thesis deals with the development of a three-dimensional computational model of high temperature heat exchanger and decomposer for hydrogen production by the sulfur iodine thermochemical water splitting cycle. The present study is concerned with the use of a bayonet type heat exchanger that is a silicon carbide integrated decomposer (SID) which decomposes sulfuric acid to produce sulfur dioxide, oxygen and water. The Sandia National Laboratories (SNL) Integrated Decomposer is a SiC based design concept that uses a SID for boiling, superheating and decomposing functions where the temperatures are above 250°C; From the literature review it can be found that …
Temperature And Silicon Effects On Tensile And Corrosion Behavior Of Chronium-Molybdenum Steel, Hanumantha Rao Chava
Temperature And Silicon Effects On Tensile And Corrosion Behavior Of Chronium-Molybdenum Steel, Hanumantha Rao Chava
UNLV Retrospective Theses & Dissertations
Martensitic P91 grade steels containing 0.48, 0.96, 1.28 and 1.77 weight percent (wt%) silicon (Si) have been tested for evaluation of their tensile properties at temperatures ranging from ambient to 550°C. The effect of activation using accelerator-driven electron beams on the room-temperature tensile properties of steels containing 0.48 and 1.28 wt% Si has also been investigated. The results indicate that all four heats of steel exhibited dynamic strain ageing at temperatures up to 400°C. The activated specimens showed enhanced tensile strength but reduced ductility with increasing activation time, indicating radiation hardening of the tested materials. The electrochemically-polarized specimens showed more …
The Effect Of Temperature On Development And Behavior Of Relict Leopard Frog Tadpoles (Rana Onca), Jeffrey Abraham Goldstein
The Effect Of Temperature On Development And Behavior Of Relict Leopard Frog Tadpoles (Rana Onca), Jeffrey Abraham Goldstein
UNLV Retrospective Theses & Dissertations
Relict Leopard frogs (Rana onca) are found in thermal springs with water temperatures in excess of 30°C at the source but it's unknown whether tadpoles require reintroduction sites with specific thermal conditions for development. Tadpole survivorship at 20, 25 and 30°C was 84, 93.8, and 66%, respectively, while none survived at 35°C. Time to metamorphosis was significantly shorter for 25°C acclimation group (62+/-8 days) followed by the 30° (106+/-51 days) and 20°C (260+/-47 days) acclimation groups. Development was arrested in the 15°C acclimated group and survivorship declined to 63.8% after 191 days. However, 80% of the surviving larvae completed metamorphosis …
Applying Of Mechanical Failure Criteria Of Brittle Material To The Design Of High Temperature Heat Exchanger, Taha Mohamed
Applying Of Mechanical Failure Criteria Of Brittle Material To The Design Of High Temperature Heat Exchanger, Taha Mohamed
UNLV Retrospective Theses & Dissertations
Previous studies have suggested using a ceramic high temperature heat exchanger as a sulfuric acid decomposer for hydrogen production within the sulfur iodine thermochemical cycle. The decomposer was manufactured using fused ceramic layers that allow the creation of channels with dimensions below one millimeter. The heat exchanger is expected to operate in the range of 950°C. Thermal stresses are however induced in the heat exchanger ceramic components. In this study, proper failure criteria are selected to evaluate the safety level of the ceramic components. A three-dimensional computational model is developed to investigate the fluid flow, heat transfer, stresses and chemical …
Numerical Study Of High Temperature Heat Exchanger And Decomposer For Hydrogen Production, Valery Ivanovich Ponyavin
Numerical Study Of High Temperature Heat Exchanger And Decomposer For Hydrogen Production, Valery Ivanovich Ponyavin
UNLV Retrospective Theses & Dissertations
This dissertation deals with three-dimensional computational modeling of a high temperature heat exchanger and decomposer for hydrogen production based on sulfur-iodine thermochemical water splitting cycle, a candidate cycle in the U.S. Department of Energy Nuclear Hydrogen Initiative. The conceptual design of the shell and plate decomposer is developed by Ceramatec, Inc. The hot helium from a nuclear reactor (T=975°C) is used to heat the SI (sulfuric acid) feed components (H2O, H2SO4 , SO3) to get appropriate conditions for the SI decomposition reaction (T>850°C). The inner wall of the SI decomposition part of the decomposer is coated by a catalyst …
Effects Of Temperature, Strain Rate And Silicon Content On Dynamic Strain Ageing Of Modified Chromium-Molybdenum Steel, Pankaj Kumar
Effects Of Temperature, Strain Rate And Silicon Content On Dynamic Strain Ageing Of Modified Chromium-Molybdenum Steel, Pankaj Kumar
UNLV Retrospective Theses & Dissertations
Martensitic T91 grade steels exhibited a susceptibility to dynamic strain aging (DSA) by virtue of gradually reduced failure strain (ef) and formation of serrations within a susceptible temperature range, irrespective of the silicon (Si) content. Since DSA is a thermally-activated process involving diffusion of solute elements, the effects of temperature and strain rate have been investigated. The activation energy associated with the diffusion process was gradually enhanced with increasing Si content at comparable temperatures. A maximum dislocation density was determined at 400°C at which lowest ef was observed in the engineering stress versus engineering strain diagram. The resistance to plastic …
Corrosion And Metallurgical Behavior Of Alloy C-22 For High-Temperature Applications, Raghunandan A Karamcheti
Corrosion And Metallurgical Behavior Of Alloy C-22 For High-Temperature Applications, Raghunandan A Karamcheti
UNLV Retrospective Theses & Dissertations
Austenitic Alloy C-22 has been tested for evaluation of its tensile and corrosion properties under conditions relevant to the nuclear hydrogen generation process known as the sulfur-iodine cycle. The results of tensile testing indicate that this alloy may be capable of maintaining metallurgical stability and enhanced ductility at temperatures up to 600°C. The stress-corrosion-cracking data suggest that this alloy may not undergo cracking in an acidic solution at 90°C at constant-load, the true failure stress (of) was significantly reduced under a slow-strain-rate condition using both smooth and notched specimens. The magnitude of the critical potentials determined by a polarization technique …
High-Temperature Deformation And Environment-Induced Degradation Of Waspaloy, Jagadesh K Yelavarthi
High-Temperature Deformation And Environment-Induced Degradation Of Waspaloy, Jagadesh K Yelavarthi
UNLV Retrospective Theses & Dissertations
The tensile properties of Waspaloy, a candidate structural material to be used in nuclear hydrogen generation, were evaluated at temperatures up to 1000°C. The results indicate that this alloy was capable of maintaining appreciably high tensile strength up to 600°C, followed by a substantial drop beyond this temperature. Between ambient temperature and 300°C, the failure strain was lowest at 300°C due to a maximum dislocation density, as determined by transmission electron microscopy. The lowest ductility was, however, observed at 800°C, possibly due to the formation of brittle sigma phase. The cracking susceptibility of Waspaloy in an acidic solution was enhanced …
Characterization Of Alloy C-276 As A Structural Material For High-Temperature Heat Exchangers, Narendra V Kothapalli
Characterization Of Alloy C-276 As A Structural Material For High-Temperature Heat Exchangers, Narendra V Kothapalli
UNLV Retrospective Theses & Dissertations
This investigation was focused on characterizing the high-temperature tensile behavior and corrosion susceptibility of nickel-based Alloy C-276, a leading structural material for heat-exchangers in nuclear hydrogen generation. The tensile properties, evaluated at different temperatures, indicate that both the yield strength and ultimate tensile strength were gradually reduced with increasing temperature. However, the ductility parameters were not significantly influenced by the testing temperature. While no failures were observed in stress corrosion cracking (SCC) tests in an acidic solution under a constant-load, the true failure stress (sigmaf) was significantly reduced under a slow-strain-rate condition using both smooth and notched specimens. The critical …
Cfd Modeling Of Compact Offset Strip-Fin High Temperature Heat Exchanger, Sundaresan Subramanian
Cfd Modeling Of Compact Offset Strip-Fin High Temperature Heat Exchanger, Sundaresan Subramanian
UNLV Retrospective Theses & Dissertations
This thesis deals with the development of a numerical model to predict the overall performance of an advanced high temperature heat exchanger (HTHX) design, up to 1000°C, for the production of hydrogen by the sulfur iodine thermo-chemical cycle. The present study considers an offset strip-fin type compact high temperature heat exchanger made of liquid silicon impregnated carbon composite (SiC). The ceramic matrix composite material (CMC) is manufactured by impregnating the silicon into the pores of the carbon composites. The prototype heat exchanger is designed to operate at a thermal power of 50 MW. The design is an offset strip-fin, hybrid …
Performance Of Waspaloy At Elevated Temperature For Heat Exchanger Applications, Lalit Savalia
Performance Of Waspaloy At Elevated Temperature For Heat Exchanger Applications, Lalit Savalia
UNLV Retrospective Theses & Dissertations
This investigation was focused on characterizing the high-temperature tensile behavior and corrosion susceptibility of the nickel-based alloy Waspaloy, which is a candidate structural material for heat exchangers in the nuclear hydrogen generation program. The tensile properties, evaluated at three different temperatures, indicate that both yield and ultimate tensile strength were gradually reduced with increasing temperatures. While no failures were observed in stress corrosion cracking (SCC) tests in an acidic solution under a constant-load, the true failure stress (sigmaf) was reduced to some extent under a slow-strain-rate condition using both smooth and notched specimens. The critical potentials, determined in a similar …
Effects Of Temperature And Dissolved Lithium Perchlorate On The Viscoelastic And Dynamic Properties Of Poly(Ethylene Oxide), (Peo) Melts, Radoslav B Bogoslovov
Effects Of Temperature And Dissolved Lithium Perchlorate On The Viscoelastic And Dynamic Properties Of Poly(Ethylene Oxide), (Peo) Melts, Radoslav B Bogoslovov
UNLV Retrospective Theses & Dissertations
Poly(ethylene oxide)/lithium perchlorate (PEO/LiClO4) complexes are widely studied as a prototype solid polymer electrolyte in rechargeable lithium-polymer batteries. Characterizing the structure and dynamics of the system in its molten state is important for understanding the role of the polymer environment in lithium ion transport and conductivity. A fiber-optic coupled Fabry-Perot interferometer is employed in the investigation of the electrolyte viscoelastic and dynamic properties, which are both related to the intrachain local mobility and therefore to ion diffusion. The properties of the system are studied as a function of composition, temperature, and frequency. Structural relaxation processes are observed both in the …
Corrosion And High-Temperature Deformation Characteristics Of A Target Structural Material For Transmutation Applications, Srinivasa Rao Kukatla
Corrosion And High-Temperature Deformation Characteristics Of A Target Structural Material For Transmutation Applications, Srinivasa Rao Kukatla
UNLV Retrospective Theses & Dissertations
Tensile properties of quenched and tempered martensitic Alloy EP 823, a target structural material, have been evaluated at temperatures ranging from ambient to 600°C as a function of three different tempering times. The susceptibility to stress corrosion cracking and localized corrosion (pitting and crevice) behavior was determined by using slow-strain-rate (SSR) and cyclic potentiodynamic polarization (CPP) techniques, respectively. The results of tensile testing indicate that the yield strength and ultimate tensile strength were gradually reduced with increasing temperature. However, as expected, the ductility parameters were enhanced at elevated temperatures due to increased plasticity. The results of SSR testing, in the …
Elevated Temperature Mechanical Properties And Corrosion Characteristics Evaluation Of Alloy Ht-9, Bhagath Yarlagadda
Elevated Temperature Mechanical Properties And Corrosion Characteristics Evaluation Of Alloy Ht-9, Bhagath Yarlagadda
UNLV Retrospective Theses & Dissertations
This thesis presents the results of tensile testing, stress corrosion cracking (SCC) and localized corrosion studies of Alloy HT-9, which is currently being considered as a target structural material for transmutation applications. The results of tensile testing indicate that the yield strength and the ultimate tensile strength were gradually reduced with increasing temperature, but the ductility parameters were enhanced due to increased plastic deformation, irrespective of the tempering time. The results of SCC testing in the 90°C acidic solution, performed by the slow-strain-rate (SSR) technique, revealed higher failure stress (sigmaf) at longer tempering time. Localized corrosion studies conducted by polarization …
Temperature And Mold Size Effects On Density Gradients And Mechanical Properties In A Polyurethane Foam System, Dacia J Jackovich
Temperature And Mold Size Effects On Density Gradients And Mechanical Properties In A Polyurethane Foam System, Dacia J Jackovich
UNLV Retrospective Theses & Dissertations
Rigid polyurethane foams can be used as a thermal or vibration insulator and energy absorption material. They are often molded directly in place, where a smooth, thin skin forms between the mold and the cellular structure of the foam. Density gradients and the skin are shown to have an effect on the mechanical properties of the foam; This work will investigate the effects of processing temperature and mold size on the average density, density gradient, compressive modulus, and compressive strength, for a molded free rise, water blown polyurethane foam system. Four processing temperatures are used during foam fabrication: 25°C, 40°C, …
Identification Of Dynamic Properties Of Materials For The Spent Nuclear Fuel Package At Elevated Temperatures, Sirisha Dusi
Identification Of Dynamic Properties Of Materials For The Spent Nuclear Fuel Package At Elevated Temperatures, Sirisha Dusi
UNLV Retrospective Theses & Dissertations
This thesis attempts to experimentally identify the dynamic properties of materials for the spent nuclear fuel package at elevated temperatures. The implementation of the project involves a number of steps. First, candidate materials for the nuclear fuel package and the appropriate testing systems were identified [15]. Second, fixtures for tensile testing at elevated temperatures using two machines, namely MTS and Instron Dynatup testing machines were designed and manufactured to make them compatible with the room temperature fixture. Third, experimental procedures for elevated temperature testing of materials are proposed for the two testing machines. Finally, impact testing for the candidate materials …
A Study Of Thermal Exchange In A Thermophotovoltaic (Tpv) System At Moderate Temperature, Yan Xu
A Study Of Thermal Exchange In A Thermophotovoltaic (Tpv) System At Moderate Temperature, Yan Xu
UNLV Retrospective Theses & Dissertations
A numerical simulation study is reported on the thermal exchange in an evacuated parallel-plate system consisting of an emitter and a photovoltaic (PV) material with the emitter temperature between 350K and 550K. Although higher temperature (and thus higher power output) thermophotovoltaic systems have been of interest previously, the focus here is on systems that can not achieve high temperatures, like micromachines. The study examines the electrical power output and power generation efficiency for four kinds of emissivity variations for the heat source coupled with three different compounds of {dollar}\rm In\sb{(x)}Ga\sb{(1-x)}As{dollar} PV materials. The results show that a 25% Ho YAG …
Low-Temperature Molecular Beam Epitaxy Of Gallium Arsenide Antisite Incorporation And Rheed Oscillations: A Theoretical Study, Natarajan Krishnan
Low-Temperature Molecular Beam Epitaxy Of Gallium Arsenide Antisite Incorporation And Rheed Oscillations: A Theoretical Study, Natarajan Krishnan
UNLV Retrospective Theses & Dissertations
Surface dynamics dominate the incorporation of charged and neutral antisite arsenic and the temporal variation of reflection high energy electron diffraction (RHEED) intensity in the low temperature (LT) molecular beam epitaxy (MBE) of (100) gallium arsenide (GaAs). A comprehensive rate equation model is proposed based on the presence and dynamics of a physisorbed arsenic (PA) riding the growth surface which dictates the incorporation and concentration of antisites and the RHEED oscillations (ROs) behavior. The dependence of antisite concentrations on growth parameters can be explained based on the saturation of the PA layer coverage at a monolayer and the competing rate …
Antisite Arsenic Incorporation In The Low-Temperature Molecular Beam Epitaxy Of Gallium Arsenide, Sivakumar Muthuvenkatraman
Antisite Arsenic Incorporation In The Low-Temperature Molecular Beam Epitaxy Of Gallium Arsenide, Sivakumar Muthuvenkatraman
UNLV Retrospective Theses & Dissertations
A stochastic model for simulating the growth processes during the low temperature molecular beam epitaxy of gallium arsenide is developed. The model includes the presence and dynamics of a weakly bound physisorbed state for arsenic. Three different kinetic models with a combination of surface kinetic processes such as incorporation of antisite arsenic, evaporation of antisite arsenic and incorporation of regular arsenic, were considered. The kinetic model which includes all three surface processes was the best model. The activation energy of 1.16eV for the evaporation of antisite arsenic from our model is in good agreement with theoretical estimates. At constant substrate …
Remote Controlled Imaging Apparatus For A High-Temperature Environment, Chanaka Joseph Anthony Fernando
Remote Controlled Imaging Apparatus For A High-Temperature Environment, Chanaka Joseph Anthony Fernando
UNLV Retrospective Theses & Dissertations
A test tunnel at Yucca Mountain is to be equipped with a mobile camera system, which can record images both at infrared and visible wavelengths at an ambient temperature to 300 degrees Centigrade (300{dollar}\sp\circ{dollar}C). This measurement is to be taken over the entire 50 meter length of the tunnel. The imaging apparatus consists of a remote section equipped with cameras, pan unit and wireless communication units, all of which must be designed to operate at 300{dollar}\sp\circ{dollar}C for up to 60 minutes. The remote sensing section is to be controlled from a computer system located outside the high-temperature zone. The project …
Gallium Arsenide Molecular Beam Epitaxy: Low Temperature And Surfactant-Mediated, Vamsee Krishna Pamula
Gallium Arsenide Molecular Beam Epitaxy: Low Temperature And Surfactant-Mediated, Vamsee Krishna Pamula
UNLV Retrospective Theses & Dissertations
The reflection high-energy electron diffraction (RHEED) specular spot intensity oscillations that were obtained during low-temperature regime and surfactant mediated regime of molecular beam epitaxial (MBE) growth of GaAs is studied and explained using modified stochastic model and a rate equation model, respectively; The dynamics of the physisorbed As layer were introduced into the stochastic model by including the thermally activated processes of chemisorption into and evaporation out of the As physisorbed state. Increased scattering of the RHEED beam due to the higher physisorbed As coverage at 2:1 leads to a factor of 5 decrease in the steady-state amplitude of the …