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Immiscibility in the Fe3O4-FeCr2O4 Spinel Binary

Description: A recent thermodynamic model of mixing in spinel binaries, based on changes in cation disordering (x) between tetrahedral and octahedral sites, is investigated for applicability to the Fe{sub 3}O{sub 4}-FeCr{sub 2}O{sub 4} system under conditions where incomplete mixing occurs. Poor agreement with measured consolute solution temperature and solvus is attributed to neglect of: (1) ordering of magnetic moments of cations in the tetrahedral sublattice antiparallel to the moments of those in the octahedral sublattice and (2) pair-wise electron hopping between octahedral site Fe{sup 3+} and Fe{sup 2+} ions. Disordering free energies ({Delta}G{sub D}), from which free energies of mixing are calculated, are modeled by {Delta}G{sub D} = {alpha}{chi} + {beta}{chi}{sup 2} - T(S{sub c} + {chi}{sigma}{sub el} + {gamma}{chi}{sigma}{sup mag}) where the previously-neglected effects are accommodated by: (1) adding a non-configurational entropy term to provide coupling between cation disordering and magnetic ordering and (2) revising the configurational entropy (S{sub c}) analysis. Applying the constraint {alpha} = -(2/3){beta} and regressing the existing database for Fe{sup 2+} ion disorder in Fe{sub 3}O{sub 4} gives: {beta} = -31,020 {+-} 1050 J mol{sup -1}, {sigma}{sub el}/R = -0.730 {+-} 0.081 and {gamma}, the coupling parameter between cation disordering and magnetic ordering, = -0.664 {+-} 0.075. The revised mixing model predicts a consolute solution temperature (T{sub cs}) = 600 C and a solvus at 500 C of n = 0.05 and 0.70 for the Fe(Fe{sub 1-n}Cr{sub n}){sub 2}O{sub 4} spinel binary.
Date: March 20, 2003
Creator: Ziemniak, S.E. & Castelli, R.A.
Partner: UNT Libraries Government Documents Department

Dynamic Simulation and Optimization of Nuclear Hydrogen Production Systems

Description: This project is part of a research effort to design a hydrogen plant and its interface with a nuclear reactor. This project developed a dynamic modeling, simulation and optimization environment for nuclear hydrogen production systems. A hybrid discrete/continuous model captures both the continuous dynamics of the nuclear plant, the hydrogen plant, and their interface, along with discrete events such as major upsets. This hybrid model makes us of accurate thermodynamic sub-models for the description of phase and reaction equilibria in the thermochemical reactor. Use of the detailed thermodynamic models will allow researchers to examine the process in detail and have confidence in the accurary of the property package they use.
Date: July 31, 2009
Creator: Barton, Paul I.; Kaximi, Mujid S.; Bollas, Georgios & Munoz, Patricio Ramirez
Partner: UNT Libraries Government Documents Department

Structure Map for Embedded Binary Alloy Nanocrystals

Description: The equilibrium structure of embedded nanocrystals formed from strongly segregating binary-alloys is considered within a simple thermodynamic model. The model identifies two dimensionlessinterface energies that dictate the structure, and allows prediction of the stable structure for anychoice of these parameters. The resulting structure map includes three distinct nanocrystal mor-phologies: core/shell, lobe/lobe, and completely separated spheres.
Date: September 20, 2008
Creator: Yuan, C. W.; Shin, S. J.; Liao, C. Y.; Guzman, J.; Stone, P. R.; Watanabe, M. et al.
Partner: UNT Libraries Government Documents Department

HIGH TEMPERATURE HIGH PRESSURE THERMODYNAMIC MEASUREMENTS FOR COAL MODEL COMPOUNDS

Description: The enthalpy of a fluid measured with respect to some reference temperature and pressure (enthalpy increment or Cp) is required for many engineering designs. Different techniques for determining enthalpy increments include direct measurement, integration of heat capacity as a function of temperature at constant pressure, and calculation from accurate density measurements as a function of temperature and pressure with ideal-gas enthalpies. Techniques have been developed for measurement of heat capacities using differential scanning calorimeters, but routine measurements with a precision better than 3% are rare. For thermodynamic model development, excess enthalpies or enthalpies of mixing of binary and ternary systems are generally required. Although these data can be calculated from measured values of incremental enthalpies of mixtures and corresponding pure components, the method of calculation involves subtraction of large numbers, and it is impossible to obtain accurate results from relatively accurate incremental enthalpy data. Directly measured heats of mixing provide better data for model development. In what follows, we give a brief literature survey of experimental methods available for measurement of incremental enthalpies as well as heats of mixing.
Date: February 24, 1999
Creator: Kabadi, Vinayak N.
Partner: UNT Libraries Government Documents Department

The Melting Curve and High-Pressure Chemistry of Formic Acid to 8 GPa and 600 K

Description: We have determined the melting temperature of formic acid (HCOOH) to 8.5 GPa using infrared absorption spectroscopy, Raman spectroscopy and visual observation of samples in a resistively heated diamond-anvil cell. The experimentally determined melting curve compares favorably with a two-phase thermodynamic model. Decomposition reactions were observed above the melting temperature up to a pressure of 6.5 GPa, where principal products were CO{sub 2}, H{sub 2}O and CO. At pressures above 6.5 GPa, decomposition led to solid-like reaction products. Infrared and Raman spectra of these recovered products indicate that pressure affects the nature of carbon-carbon bonding.
Date: April 13, 2005
Creator: Montgomery, W; Zaug, J M; Howard, W M; Goncharov, A F; Crowhurst, J C & Jeanloz, R
Partner: UNT Libraries Government Documents Department

TRANSPORT AND REDUCTION POSSIBILITIES DURING TPBAR EXTRACTION

Description: In light of the discovery of the activated zinc 65 in the TEF process piping, a discussion of potential sources and mechanisms for the production of this species has been initiated. A suspected source is the presence of Cu as a contaminant in many of the alloy components that comprise the TPBARs and the presence of Zn as a contaminant in the aluminide coating. These two sources are expected to produce metallic transmutation products that could be mobile and be extracted from the metallic components of the TPBARs. Another potential source is the presence of ZnO that is present as part of the crud on the external surfaces of the TPBARs. In addition, it is conceivable to have ZnO within the TPBARs from transmutation products and subsequent oxidation reactions with water. This memo does not attempt to address all of the possible sources, nor does it derive the most likely scenarios as to how Zn or ZnO may be present in the TPBARs it merely posits that it is present as a transmutation product and if present, elementally, it may be mobile under high vacuum conditions at high temperatures as indicated by the pressure temperature curve shown in Fig. 1. Further, this document shows that it is thermodynamically feasible to reduce ZnO to Zn by solid state reactions of the ZnO with other metallic components in the TPBARs. However, for these reactions to occur, the ZnO must be in contact with the more active metal so that the chemical reactions can occur. The proposed reactions are based on equilibrium thermodynamics. For simplicity, they do not take into account the quantities of the various materials, the compositions, the effect of alloying, or other technical issues, they are intended only to provide feasibility for the reduction reactions. A more complete thermodynamic model ...
Date: May 19, 2008
Creator: Korinko, P
Partner: UNT Libraries Government Documents Department

Gasdynamic Model of Turbulent Combustion in TNT Explosions

Description: A model is proposed to simulate turbulent combustion in confined TNT explosions. It is based on: (i) the multi-component gasdynamic conservation laws, (ii) a fast-chemistry model for TNT-air combustion, (iii) a thermodynamic model for frozen reactants and equilibrium products, (iv) a high-order Godunov scheme providing a non-diffusive solution of the governing equations, and (v) an ILES approach whereby adaptive mesh refinement is used to capture the energy bearing scales of the turbulence on the grid. Three-dimensional numerical simulations of explosion fields from 1.5-g PETN/TNT charges were performed. Explosions in six different chambers were studied: three calorimeters (volumes of 6.6-l, 21.2-l and 40.5-l with L/D = 1), and three tunnels (L/D = 3.8, 4.65 and 12.5 with volumes of 6.3-l) - to investigate the influence of chamber volume and geometry on the combustion process. Predicted pressures histories were quite similar to measured pressure histories for all cases studied. Experimentally, mass fraction of products, Y{sub p}{sup exp}, reached a peak value of 88% at an excess air ratio of twice stoichiometric, and then decayed with increasing air dilution; mass fractions Y{sub p}{sup calc} computed from the numerical simulations followed similar trends. Based on this agreement, we conclude that the dominant effect that controls the rate of TNT combustion with air is the turbulent mixing rate; the ILES approach along with the fast-chemistry model used here adequately captures this effect.
Date: January 8, 2010
Creator: Kuhl, A L; Bell, J B & Beckner, V E
Partner: UNT Libraries Government Documents Department

Low-density ionization behavior

Description: As part of a continuing study of the physics of matter under extreme conditions, I give some results on matter at extremely low density. In particular I compare a quantum mechanical calculation of the pressure for atomic hydrogen with the corresponding pressure given by Thomas-Fermi theory. (This calculation differs from the ``confined atom`` approximation in a physically significant way.) Since Thomas-Fermi theory in some sense, represents the case of infinite nuclear charge, these cases should represent extremes. Comparison is also made with Saha theory, which considers ionization from a chemical point of view, but is weak on excited-state effects. In this theory, the pressure undergoes rapid variation as electron ionization levels are passed. This effect is in contrast to the smooth behavior of the Thomas-Fermi fixed temperature, complete ionization occurs in the low density limit, I study the case where the temperature goes appropriately to zero with the density. Although considerable modification is required, Saha theory is closer to the actual results for this case than is Thomas-Fermi theory.
Date: April 1, 1995
Creator: Baker, G.A. Jr.
Partner: UNT Libraries Government Documents Department

Thermodynamic Cycle Analysis Program (TCAP)

Description: This report describes the Thermodynamic Cycle Analysis Program (TCAP) software developed in support of the Collaborative Advanced Gas Turbine (CAGT) research project. The goal of the CAGT project was to evaluate different configurations of gas turbine-based power generation cycles. TCAP software enables the user to graphically construct power cycles that incorporate a variety of components such as compressors, turbines, heat exchangers, and reactors. The user also specifies the input condition of the working fluid and the parameters associated with each component. TCAP then calculates the composition and thermodynamic properties of the working fluid at every point in the cycle. From this data, TCAP calculates the overall thermodynamic efficiency of the cycle and emission levels of specific chemicals. Thermodynamic and chemical kinetic data are based on the Chemkin family of application codes and libraries.
Date: January 1, 1997
Creator: Yoshimura, A.S.
Partner: UNT Libraries Government Documents Department

An analytical method of predicting Lee-Kesler-Ploecker binary interaction coefficients: Part 1, For non-polar hydrocarbon mixtures

Description: An analytical method is proposed for finding numerical values of binary interaction coefficients for non-polar hydrocarbon mixtures when the Lee-Kesler (LK) equation of state is applied. The method is based on solving simultaneous equations, which are Ploecker`s mixing rules for pseudocritical parameters of a mixture, and the Lee-Kesler equation for the saturation line. For a hydrocarbon mixture, the method allows prediction of {kappa}{sub ij} interaction coefficients (ICs) which are close to values obtained by processing experimental p-v-t data on the saturation line and subsequent averaging. For mixtures of hydrocarbon molecules containing from 2 to 9 carbon atoms, the divergence between calculated and experimentally based ICs is no more than {plus_minus}0.4%. The possibility of extending application of this method to other non-polar substances is discussed.
Date: December 31, 1994
Creator: Sand, J.R.
Partner: UNT Libraries Government Documents Department

CO2 Capture by Absorption With Potassium Carbonate

Description: The objective of this work is to improve the process for CO{sub 2} capture by alkanolamine absorption/stripping by developing an alternative solvent, aqueous K{sub 2}CO{sub 3} promoted by piperazine. A rigorous thermodynamic model has been developed with a stand-alone FORTRAN code to represent the CO{sub 2} vapor pressure and speciation of the new solvent. Parameters have been developed for use of the electrolyte NRTL model in AspenPlus. Analytical methods have been developed using gas chromatography and ion chromatography. The heat exchangers for the pilot plant have been ordered.
Date: April 1, 2003
Creator: Rochelle, Gary T.; Chen, Eric; Cullinane, J. Tim; Hilliard, Marcus & Jones, Terraun
Partner: UNT Libraries Government Documents Department

Condensation analysis for plate-frame heat exchangers

Description: A theoretical analysis is presented to predict single component and binary-mixture condensation in plate-frame heat exchangers. A thermodynamic property model based on the Peng-Robinson equation of state was developed for the binary-mixture equilibrium and formulated into a performance prediction program. A set of equations was formulated and a calculation algorithm was developed to predict the local rate of heat and mass transfer for binary mixtures. Friction-factor and heat-transfer-coefficient correlations were developed using experimental data obtained with ammonia condensation. The role of the mass-transfer resistance associated with the condensation process were analyzed for a propane/butane mixture using two limiting cases: (1) no liquid-phase mass-transfer resistance, and (2) infinite liquid-phase mass-transfer resistance. The results show that the vapor-phase mass-transfer resistance is the controlling mechanism for binary-mixture condensation.
Date: July 1, 1995
Creator: Arman, B. & Rabas, T.J.
Partner: UNT Libraries Government Documents Department

Exploratory Research on Simulation of CO2-Brine-Mineral Interactions

Description: Application of many carbon sequestration strategies requires knowledge of thermodynamic properties for the extremely complex chemical system of CO{sub 2}-SO{sub 2}-H{sub 2}O-NaCl-CaCl{sub 2}-MgCl{sub 2}. This University Coal Research Phase I program has been successful and highly productive in exploring an approach to develop an equation of state (EOS) to describe thermodynamic properties in the above chemical system. We have compiled available laboratory experimental data and thermodynamic models, and evaluated their appropriateness for the carbon sequestration process. Based on this literature review, we provided an improved CO{sub 2} solubility model for the CO{sub 2}-H{sub 2}O-NaCl system, which incorporates newly available experimental measurements funded by DOE, and is valid in temperature range from 273 to 533 K, pressure from 0 to 2000 bar, and salinity from 0 to 4.5 molality of NaCl equivalent. The improved model also greatly improves the computational efficiency of CO{sub 2} solubility calculations and thus is better suited to be incorporated into large computer simulation models (e.g., reservoir simulation models). The literature review and model development provided insights of the data needs and directions for future work. Synergetic collaboration with DOE scientists has resulted in simulations of injected CO{sub 2} fate in sandstone aquifer with a one-dimensional numerical coupled reactive transport model. We evaluated over 100 references on CO{sub 2} solubility and submitted two manuscripts to peer-reviewed journals. One paper has been accepted for publication in ''Environmental Geosciences''.
Date: November 1, 2005
Creator: Zhu, Chen & Chiang, Shiao hung
Partner: UNT Libraries Government Documents Department

Superheating and supercooling of Ge nanocrystals embedded inSiO2

Description: Free-standing nanocrystals exhibit a size-dependant thermodynamic melting point reduction relative to the bulk melting point that is governed by the surface free energy. The presence of an encapsulating matrix, however, alters the interface free energy of nanocrystals and their thermodynamic melting point can either increase or decrease relative to bulk. Furthermore, kinetic contributions can significantly alter the melting behaviors of embedded nanoscale materials. To study the effect of an encapsulating matrix on the melting behavior of nanocrystals, we performed in situ electron diffraction measurements on Ge nanocrystals embedded in a silicon dioxide matrix. Ge nanocrystals were formed by multi-energy ion implantation into a 500 nm thick silica thin film on a silicon substrate followed by thermal annealing at 900 C for 1 h. We present results demonstrating that Ge nanocrystals embedded in SiO{sub 2} exhibit a 470 K melting/solidification hysteresis that is approximately symmetric about the bulk melting point. This unique behavior, which is thought to be impossible for bulk materials, is well described using a classical thermodynamic model that predicts both kinetic supercooling and kinetic superheating. The presence of the silica matrix suppresses surface pre-melting of nanocrystals. Therefore, heterogeneous nucleation of both the liquid phase and the solid phase are required during the heating and cooling cycle. The magnitude of melting hysteresis is governed primarily by the value of the liquid Ge/solid Ge interface free energy, whereas the relative values of the solid Ge/matrix and liquid Ge/matrix interface free energies govern the position of the hysteresis loop in absolute temperature.
Date: August 21, 2006
Creator: Xu, Q.; Sharp, I.D.; Yuan, C.W.; Yi, D.O.; Liao, C.Y.; Glaeser,A.M. et al.
Partner: UNT Libraries Government Documents Department

Comprehensive Approaches to Multiphase Flows in Geophysics - Application to nonisothermal, nonhomogenous, unsteady, large-scale, turbulent dusty clouds I. Hydrodynamic and Thermodynamic RANS and LES Models

Description: The objective of this manuscript is to fully derive a geophysical multiphase model able to ''accommodate'' different multiphase turbulence approaches; viz., the Reynolds Averaged Navier-Stokes (RANS), the Large Eddy Simulation (LES), or hybrid RANSLES. This manuscript is the first part of a larger geophysical multiphase project--lead by LANL--that aims to develop comprehensive modeling tools for large-scale, atmospheric, transient-buoyancy dusty jets and plume (e.g., plinian clouds, nuclear ''mushrooms'', ''supercell'' forest fire plumes) and for boundary-dominated geophysical multiphase gravity currents (e.g., dusty surges, diluted pyroclastic flows, dusty gravity currents in street canyons). LES is a partially deterministic approach constructed on either a spatial- or a temporal-separation between the large and small scales of the flow, whereas RANS is an entirely probabilistic approach constructed on a statistical separation between an ensemble-averaged mean and higher-order statistical moments (the so-called ''fluctuating parts''). Within this specific multiphase context, both turbulence approaches are built up upon the same phasic binary-valued ''function of presence''. This function of presence formally describes the occurrence--or not--of any phase at a given position and time and, therefore, allows to derive the same basic multiphase Navier-Stokes model for either the RANS or the LES frameworks. The only differences between these turbulence frameworks are the closures for the various ''turbulence'' terms involving the unknown variables from the fluctuating (RANS) or from the subgrid (LES) parts. Even though the hydrodynamic and thermodynamic models for RANS and LES have the same set of Partial Differential Equations, the physical interpretations of these PDEs cannot be the same, i.e., RANS models an averaged field, while LES simulates a filtered field. In this manuscript, we also demonstrate that this multiphase model fully fulfills the second law of thermodynamics and fulfills the necessary requirements for a well-posed initial-value problem. In the next manuscripts, we will further develop specific closures for ...
Date: September 5, 2005
Creator: Dartevelle, S.
Partner: UNT Libraries Government Documents Department

Non-Ideal Behavior in Solvent Extraction

Description: This report presents a summary of the work performed to meet FCR&D level 3 milestone M31SW050801, 'Complete the year-end report summarizing FY11 experimental and modeling activities.' This work was carried out under the auspices of the Non-Ideality in Solvent Extraction Systems FCR&D work package. The report summarizes our initial considerations of potential influences that non-ideal chemistry may impose on computational prediction of outcomes in solvent extraction systems. The report is packaged into three separate test cases where a robustness of the prediction by SXFIT program is under scrutiny. The computational exercises presented here emphasize the importance of accurate representation of both an aqueous and organic mixtures when modeling liquid-liquid distribution systems. Case No.1 demonstrates that non-ideal behavior of HDEHP in aliphatic diluents, such as n-dodecane, interferes with the computation. Cases No.2 and No.3 focus on the chemical complexity of aqueous electrolyte mixtures. Both exercises stress the need for an improved thermodynamic model of an aqueous environment present in the europium distribution experiments. Our efforts for year 2 of this project will focus on the improvements of aqueous and non-aqueous solution models using fundamental physical properties of mixtures acquired experimentally in our laboratories.
Date: September 1, 2011
Creator: Zalupski, Peter
Partner: UNT Libraries Government Documents Department

Thermodynamic Model of Aluminum Combustion in SDF Explosions

Description: Thermodynamic states encountered during combustion of Aluminum powder in Shock-Dispersed-Fuel (SDF) explosions were analyzed with the Cheetah code. Results are displayed in the Le Chatelier diagram: the locus of states of specific internal energy versus temperature. Accuracy of the results was confirmed by comparing the fuel and products curves with the heats of detonation and combustion, and species composition as measured in bomb calorimeter experiments. Results were fit with analytic functions u = f(T) suitable for specifying the thermodynamic properties required for gas-dynamic models of combustion in explosions.
Date: June 19, 2006
Creator: Kuhl, . L
Partner: UNT Libraries Government Documents Department

A thermodynamic model of the hydrolysis of microcline in acid sulfate solutions

Description: A theoretical model of the hydrolysis of microcline by a hydrothermal solution has been determined for a closed system at constant temperature. Hypothetical solution compositions and temperatures were chosen to match the known geothermal system at Roosevelt Hot Springs, Utah. The calculated reaction paths indicate that the overall reaction process is an exchange of potassium from the reactant mineral, microcline, for hydrogen from the solution. Aluminum is nearly conserved among solid phases. The amount of microcline reacted per kilogram of solution before overall equilibrium is reached is a function of temperature and initial solution pH. Since the system is closed and at constant temperature natural conditions are not reproduced well enough to apply the model as a geothermometer. The reaction paths suggest qualitative models of alteration mineral zoning patterns that are similar to zoning at Roosevelt Hot Springs, utah; Steamboat Springs, Nevada, and Butte, Montana. The models presented view alteration zoning as a function of temperature and pH gradients within homogeneous host rocks where microcline and quartz are abundant.
Date: December 1, 1976
Creator: Dedolph, R.E. & Parry, W.T.
Partner: UNT Libraries Government Documents Department

Wax Point Determinations Using Acoustic Resonance Spectroscopy

Description: The thermodynamic characterization of the wax point of a given crude is essential in order to maintain flow conditions that prevent plugging of undersea pipelines. This report summarizes the efforts made towards applying an Acoustic Cavity Resonance Spectrometer (ACRS) to the determination of pressures and temperatures at which wax precipitates from crude. Phillips Petroleum Company, Inc., the CRADA participant, supplied the ACRS. The instrumentation was shipped to Dr. Thomas Schmidt of ORNL, the CRADA contractor, in May 2000 after preliminary software development performed under the guidance of Dr. Samuel Colgate and Dr. Evan House of the University of Florida, Gainesville, Fl. Upon receipt it became apparent that a number of modifications still needed to be made before the ACRS could be precisely and safely used for wax point measurements. This report reviews the sequence of alterations made to the ACRS, as well as defines the possible applications of the instrumentation once the modifications have been completed. The purpose of this Cooperative Research and Development Agreement (CRADA) between Phillips Petroleum Company, Inc. (Participant) and Lockheed Martin Energy Research Corporation (Contractor) was the measurement of the formation of solids in crude oils and petroleum products that are commonly transported through pipelines. This information is essential in the proper design, operation and maintenance of the petroleum pipeline system in the United States. Recently, new petroleum discoveries in the Gulf of Mexico have shown that there is a potential for plugging of undersea pipeline because of the precipitation of wax. It is important that the wax points of the expected crude oils be well characterized so that the production facilities for these new wells are capable of properly transporting the expected production. The goal of this work is to perform measurements of solids formation in crude oils and petroleum products supplied by the Participant. ...
Date: June 1, 2001
Creator: Bostick, D.T.; Jubin, R.T. & Schmidt, T.W.
Partner: UNT Libraries Government Documents Department

Evaluation of Wax Deposition and Its Control During Production of Alaska North Slope Oils

Description: Due to increasing oil demand, oil companies are moving into arctic environments and deep-water areas for oil production. In these regions of lower temperatures, wax deposits begin to form when the temperature in the wellbore falls below wax appearance temperature (WAT). This condition leads to reduced production rates and larger pressure drops. Wax problems in production wells are very costly due to production down time for removal of wax. Therefore, it is necessary to develop a solution to wax deposition. In order to develop a solution to wax deposition, it is essential to characterize the crude oil and study phase behavior properties. The main objective of this project was to characterize Alaskan North Slope crude oil and study the phase behavior, which was further used to develop a dynamic wax deposition model. This report summarizes the results of the various experimental studies. The subtasks completed during this study include measurement of density, molecular weight, viscosity, pour point, wax appearance temperature, wax content, rate of wax deposition using cold finger, compositional characterization of crude oil and wax obtained from wax content, gas-oil ratio, and phase behavior experiments including constant composition expansion and differential liberation. Also, included in this report is the development of a thermodynamic model to predict wax precipitation. From the experimental study of wax appearance temperature, it was found that wax can start to precipitate at temperatures as high as 40.6 C. The WAT obtained from cross-polar microscopy and viscometry was compared, and it was discovered that WAT from viscometry is overestimated. From the pour point experiment it was found that crude oil can cease to flow at a temperature of 12 C. From the experimental results of wax content, it is evident that the wax content in Alaskan North Slope crude oil can be as high as 28.57%. ...
Date: December 31, 2008
Creator: Zhu, Tao; Walker, Jack A. & Liang, J.
Partner: UNT Libraries Government Documents Department

An Investigation Into the Mechanics of Single Crystal Turbine Blades With a View Towards Enhancing Gas Turbine Efficiency

Description: The demand for increased efficiency of gas turbines used in power generation and aircraft applications has fueled research into advanced materials for gas turbine blades that can withstand higher temperatures in that they have excellent resistance to creep. The term ''Superalloys'' describes a group of alloys developed for applications that require high performance at elevated temperatures. Superalloys have a load bearing capacity up to 0.9 times their melting temperature. The objective of the investigation was to develop a thermodynamic model that can be used to describe the response of single crystal superalloys that takes into account the microstructure of the alloy within the context of a continuum model. Having developed the model, its efficacy was to be tested by corroborating the predictions of the model with available experimental data. Such a model was developed and it is implemented in the finite element software ABAQUS/STANDARD through a user subroutine (UMAT) so that the model can be used in realistic geometries that correspond to turbine blades.
Date: May 5, 2006
Creator: Rajagopal, K. R. & Rao, I. J.
Partner: UNT Libraries Government Documents Department

EFFECT OF HEATING RATE ON THE THERMODYNAMIC PROPERTIES OF PULVERIZED COAL

Description: This semi-annual technical progress report describes work performed under DOE Grant No. DE-FG22-96PC96224 during the period March 24, 1999 to September 23, 1999 which covers the last (sixth) six months of the project. During this reporting period, extraction of devolatilization time-scales and temperature data at these time-scales analyzing the high-speed films taken during the experiments was complete. Also a new thermodynamic model was developed to predict the heat transfer behavior for coal particles subjected to a range of heating rates using one approach based on the analogy of polymers. Sensitivity analyses of this model suggest that bituminous coal particles behave like polymers during rapid heating on the order of 10{sup 4}-10{sup 7} K/s. At these heating rates during the early stages within the first few milliseconds of heating time, the vibrational part of the heat capacity of the coal molecules appears to be still frozen but during the transition from heat-up to devolatization, the heat capacity appears to attain a sudden jump in its value as in the case of polymers. There are few data available in the coal literature for 10{sup 2}-10{sup 3} K/s obtained by UTRC in their previous studies. These data were obtained for a longer heating duration on the order of several seconds as opposed to the 10 milliseconds heating time in the single particle experiments discussed above. The polymer analogy model is being modified to include longer heating time on the order of several seconds to test these data. It is expected that the model might still do a good job in the case of these larger heating time but very low heating rate experiments. Completion of the numerical analysis of the experimental data and preparation of the final report are in progress.
Date: November 2, 1999
Creator: Sampath, Ramanathan
Partner: UNT Libraries Government Documents Department

Aluminosilicate Formation in High Level Waste Evaporators: A Mechanism for Uranium Accumulation

Description: High level waste Evaporators at the Savannah River Site (SRS) process radioactive waste to concentrate supernate and thus conserve tank space. In June of 1997, difficulty in evaporator operation was initially observed. This operational difficulty evidenced itself as a plugging of the evaporator's gravity drain line (GDL). The material blocking the GDL was determined to be a sodium aluminosilicate. Following a mechanical cleaning of the GDL, the evaporator was returned to service until October 1999. At this time massive deposits were discovered in the evaporator pot. As a result of the changes in evaporator chemistry and the resulting formation of aluminosilicate deposits in the evaporator, a comprehensive research and development program has been undertaken. This program is underway in order to assist in understanding the new evaporator chemistry and gain insight into the deposition phenomena. Key results from testing in FY01 have demonstrated that the chemistry of the evaporator feed favors aluminosilicate formation. Both the reaction kinetics and particle growth of the aluminosilicate material under SRS evaporator conditions has been demonstrated to occur within the residence times utilized in the SRS evaporator operation. Batch and continuous-flow experiments at known levels of supersaturation have shown a significant correlation between the deposition of aluminosilicates and mixing intensity in the vessel. Advances in thermodynamic modeling of the evaporator chemistry have been accomplished. The resulting thermodynamic model has been related to the operational history of the evaporator, is currently assisting in feed selection, and could potentially assist in expanding the operating envelopes technical baselines for evaporator operation.
Date: February 8, 2002
Creator: Wilmarth, W.R.
Partner: UNT Libraries Government Documents Department