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Isotope exchange kinetics in metal hydrides I : TPLUG model

Larson, Richard S.; James, Scott; Nilson, Robert H.

A one-dimensional isobaric reactor model is used to simulate hydrogen isotope exchange processes taking place during flow through a powdered palladium bed. This simple model is designed to serve primarily as a platform for the initial development of detailed chemical mechanisms that can then be refined with the aid of more complex reactor descriptions. The one-dimensional model is based on the Sandia in-house code TPLUG, which solves a transient set of governing equations including an overall mass balance for the gas phase, material balances for all of the gas-phase and surface species, and an ideal gas equation of state. An energy equation can also be solved if thermodynamic properties for all of the species involved are known. The code is coupled with the Chemkin package to facilitate the incorporation of arbitrary multistep reaction mechanisms into the simulations. This capability is used here to test and optimize a basic mechanism describing the surface chemistry at or near the interface between the gas phase and a palladium particle. The mechanism includes reversible dissociative adsorptions of the three gas-phase species on the particle surface as well as atomic migrations between the surface and the bulk. The migration steps are more general than those used previously in that they do not require simultaneous movement of two atoms in opposite directions; this makes possible the creation and destruction of bulk vacancies and thus allows the model to account for variations in the bulk stoichiometry with isotopic composition. The optimization code APPSPACK is used to adjust the mass-action rate constants so as to achieve the best possible fit to a given set of experimental data, subject to a set of rigorous thermodynamic constraints. When data for nearly isothermal and isobaric deuterium-to-hydrogen (D {yields} H) and hydrogen-to-deuterium (H {yields} D) exchanges are fitted simultaneously, results for the former are excellent, while those for the latter show pronounced deviations at long times. These discrepancies can be overcome by postulating the presence of a surface poison such as carbon monoxide, but this explanation is highly speculative. When the method is applied to D {yields} H exchanges intentionally poisoned by known amounts of CO, the fitting results are noticeably degraded from those for the nominally CO-free system but are still tolerable. When TPLUG is used to simulate a blowdown-type experiment, which is characterized by large and rapid changes in both pressure and temperature, discrepancies are even more apparent. Thus, it can be concluded that the best use of TPLUG is not in simulating realistic exchange scenarios, but in extracting preliminary estimates for the kinetic parameters from experiments in which variations in temperature and pressure are intentionally minimized.

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TYPE SAND Report YEAR 2011
DOIOSTI

TChem - A Software Toolkit for the Analysis of Complex Kinetic Models

Safta, Cosmin; Najm, Habib N.

The TChem toolkit is a software library that enables numerical simulations using complex chemistry and facilitates the analysis of detailed kinetic models. The toolkit provide capabilities for thermodynamic properties based on NASA polynomials and species production/consumption rates. It incorporates methods that can selectively modify reaction parameters for sensitivity analysis. The library contains several functions that provide analytically computed Jacobian matrices necessary for the efficient time advancement and analysis of detailed kinetic models.

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TYPE SAND Report YEAR 2011
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False negative rate and other performance measures of a sponge-wipe surface sampling method for low contaminant concentrations

Krauter, Paula; Einfeld, Wayne E.

Recovery of spores from environmental surfaces is known to vary due to sampling methodology, techniques, spore size and characteristics, surface materials, and environmental conditions. A series of tests were performed to evaluate a new, validated sponge-wipe method. Specific factors evaluated were the effects of contaminant concentrations and surface materials on recovery efficiency (RE), false negative rate (FNR), limit of detection (LOD) - and the uncertainties of these quantities. Ceramic tile and stainless steel had the highest mean RE values (48.9 and 48.1%, respectively). Faux leather, vinyl tile, and painted wood had mean RE values of 30.3, 25.6, and 25.5, respectively, while plastic had the lowest mean RE (9.8%). Results show a roughly linear dependence of surface roughness on RE, where the smoothest surfaces have the highest mean RE values. REs were not influenced by the low spore concentrations tested (3 x 10{sup -3} to 1.86 CFU/cm{sup 2}). The FNR data were consistent with RE data, showing a trend of smoother surfaces resulting in higher REs and lower FNRs. Stainless steel generally had the lowest mean FNR (0.123) and plastic had the highest mean FNR (0.479). The LOD{sub 90} varied with surface material, from 0.015 CFU/cm{sup 2} on stainless steel up to 0.039 on plastic. Selecting sampling locations on the basis of surface roughness and using roughness to interpret spore recovery data can improve sampling. Further, FNR values, calculated as a function of concentration and surface material, can be used pre-sampling to calculate the numbers of samples for statistical sampling plans with desired performance, and post-sampling to calculate the confidence in characterization and clearance decisions.

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TYPE SAND Report YEAR 2011
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PV performance modeling workshop summary report

Stein, Joshua

During the development of a solar photovoltaic (PV) energy project, predicting expected energy production from a system is a key part of understanding system value. System energy production is a function of the system design and location, the mounting configuration, the power conversion system, and the module technology, as well as the solar resource. Even if all other variables are held constant, annual energy yield (kWh/kWp) will vary among module technologies because of differences in response to low-light levels and temperature. A number of PV system performance models have been developed and are in use, but little has been published on validation of these models or the accuracy and uncertainty of their output. With support from the U.S. Department of Energy's Solar Energy Technologies Program, Sandia National Laboratories organized a PV Performance Modeling Workshop in Albuquerque, New Mexico, September 22-23, 2010. The workshop was intended to address the current state of PV system models, develop a path forward for establishing best practices on PV system performance modeling, and set the stage for standardization of testing and validation procedures for models and input parameters. This report summarizes discussions and presentations from the workshop, as well as examines opportunities for collaborative efforts to develop objective comparisons between models and across sites and applications.

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TYPE SAND Report YEAR 2011
DOIOSTI

Understanding the function and performance of carbon-enhanced lead-acid batteries : milestone report for the DOE Energy Storage Systems program (FY11 Quarter 1: October through December 2010)

Enos, David; Hund, Thomas D.

This report describes the status of research being performed under CRADA No. SC10/01771.00 (Lead/Carbon Functionality in VRLA Batteries) between Sandia National Laboratories and East Penn Manufacturing, conducted for the U.S. Department of Energy's Energy Storage Systems Program. The Quarter 1 Milestone was completed on time. The milestone entails conducting a thorough literature review to establish the current level of understanding of the mechanisms through which carbon additions to the negative active material improve valve-regulated lead-acid (VRLA) batteries. Most studies have entailed phenomenological research observing that the carbon additions prevent/reduce sulfation of the negative electrode; however, no understanding is available to provide insight into why certain carbons are successful while others are not. Impurities were implicated in one recent review of the electrochemical behavior of carbon additions. Four carbon samples have been received from East Penn Manufacturing and impurity contents have been analyzed. Carbon has been explored as an addition to lead-acid battery electrodes in a number of ways. Perhaps the most notable to date has been the hybrid 'Ultrabattery' developed by CSIRO where an asymmetric carbon-based electrochemical capacitor is combined with a lead-acid battery into a single cell, dramatically improving high-rate partial-state-of-charge (HRPSoC) operation. As illustrated below, the 'Ultrabattery' is a hybrid device constructed using a traditional lead-acid battery positive plate (i.e., PbO{sub 2}) and a negative electrode consisting of a carbon electrode in parallel with a lead-acid negative plate. This device exhibits a dramatically improved cycle life over traditional VRLA batteries, as well as increased charge power and charge acceptance. The 'Ultrabattery' has been produced successfully by both The Furukawa Battery Co. and East Penn Manufacturing. An example illustrating the dramatic improvement in cycle life of the Ultrabattery over a conventional VRLA battery is shown in the graph.

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TYPE SAND Report YEAR 2011
DOIOSTI

Understanding the function and performance of carbon-enhanced lead-acid batteries : milestone report for the DOE Energy Storage Systems program (FY11 Quarter 2: January through March 2011)

Enos, David; Hund, Thomas D.

This report describes the status of research being performed under CRADA No. SC10/01771.00 (Lead/Carbon Functionality in VRLA Batteries) between Sandia National Laboratories and East Penn Manufacturing, conducted for the U.S. Department of Energy's Energy Storage Systems Program. The Quarter 2 Milestone was completed on time. The milestone entails an ex situ analysis of the four carbons that have been added to the negative active material of valve-regulated lead-acid (VRLA) batteries for the purposes of this study. The four carbons selected for this study were a graphitic carbon, a carbon black, an activated carbon, and acetylene black. The morphology, crystallinity, and impurity contents of each of the four carbons were analyzed; results were consistent with previous data. Cycling on a subset of the received East Penn cells containing different carbons (and a control) has been initiated. Carbon has been explored as an addition to lead-acid battery electrodes in a number of ways. Perhaps the most notable to date has been the hybrid 'Ultrabattery' developed by CSIRO where an asymmetric carbon-based electrochemical capacitor is combined with a lead-acid battery into a single cell, dramatically improving high-rate partial-state-of-charge (HRPSoC) operation. As illustrated below, the 'Ultrabattery' is a hybrid device constructed using a traditional lead-acid battery positive plate (i.e., PbO{sub 2}) and a negative electrode consisting of a carbon electrode in parallel with a lead-acid negative plate. This device exhibits a dramatically improved cycle life over traditional VRLA batteries, as well as increased charge power and charge acceptance. The 'Ultrabattery' has been produced successfully by both The Furukawa Battery Co. and East Penn Manufacturing. An example illustrating the dramatic improvement in cycle life of the Ultrabattery over a conventional VRLA battery is shown.

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TYPE SAND Report YEAR 2011
DOIOSTI

Joint Architecture Standard (JAS) Reliable Data Delivery Protocol (RDDP) specification

Gardner, Michael T.; Hunt, Richard D.; Enderle, Justin W.; Gallegos, Daniel E.; Eldridge, John M.; Daniels, James W.

The Joint Architecture Standard (JAS) program at Sandia National Laboratories requires the use of a reliable data delivery protocol over SpaceWire. The National Aeronautics and Space Administration at the Goddard Spaceflight Center in Greenbelt, Maryland, developed and specified a reliable protocol for its Geostationary Operational Environment Satellite known as GOES-R Reliable Data Delivery Protocol (GRDDP). The JAS program implemented and tested GRDDP and then suggested a number of modifications to the original specification to meet its program specific requirements. This document details the full RDDP specification as modified for JAS. The JAS Reliable Data Delivery Protocol uses the lower-level SpaceWire data link layer to provide reliable packet delivery services to one or more higher-level host application processes. This document specifies the functional requirements for JRDDP but does not specify the interfaces to the lower- or higher-level processes, which may be implementation-dependent.

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TYPE SAND Report YEAR 2011
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River meander modeling and confronting uncertainty

Posner, Ari J.

This study examines the meandering phenomenon as it occurs in media throughout terrestrial, glacial, atmospheric, and aquatic environments. Analysis of the minimum energy principle, along with theories of Coriolis forces (and random walks to explain the meandering phenomenon) found that these theories apply at different temporal and spatial scales. Coriolis forces might induce topological changes resulting in meandering planforms. The minimum energy principle might explain how these forces combine to limit the sinuosity to depth and width ratios that are common throughout various media. The study then compares the first order analytical solutions for flow field by Ikeda, et al. (1981) and Johannesson and Parker (1989b). Ikeda's et al. linear bank erosion model was implemented to predict the rate of bank erosion in which the bank erosion coefficient is treated as a stochastic variable that varies with physical properties of the bank (e.g., cohesiveness, stratigraphy, or vegetation density). The developed model was used to predict the evolution of meandering planforms. Then, the modeling results were analyzed and compared to the observed data. Since the migration of a meandering channel consists of downstream translation, lateral expansion, and downstream or upstream rotations several measures are formulated in order to determine which of the resulting planforms is closest to the experimental measured one. Results from the deterministic model highly depend on the calibrated erosion coefficient. Since field measurements are always limited, the stochastic model yielded more realistic predictions of meandering planform evolutions. Due to the random nature of bank erosion coefficient, the meandering planform evolution is a stochastic process that can only be accurately predicted by a stochastic model.

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TYPE SAND Report YEAR 2011
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NEAMS Nuclear Waste Management IPSC : evaluation and selection of tools for the quality environment

Vigil, Dena; Edwards, Harold C.; Bouchard, Julie F.; Stubblefield, William A.

The objective of the U.S. Department of Energy Office of Nuclear Energy Advanced Modeling and Simulation Nuclear Waste Management Integrated Performance and Safety Codes (NEAMS Nuclear Waste Management IPSC) is to provide an integrated suite of computational modeling and simulation (M&S) capabilities to quantitatively assess the long-term performance of waste forms in the engineered and geologic environments of a radioactive-waste storage facility or disposal repository. These M&S capabilities are to be managed, verified, and validated within the NEAMS Nuclear Waste Management IPSC quality environment. M&S capabilities and the supporting analysis workflow and simulation data management tools will be distributed to end-users from this same quality environment. The same analysis workflow and simulation data management tools that are to be distributed to end-users will be used for verification and validation (V&V) activities within the quality environment. This strategic decision reduces the number of tools to be supported, and increases the quality of tools distributed to end users due to rigorous use by V&V activities. This report documents an evaluation of the needs, options, and tools selected for the NEAMS Nuclear Waste Management IPSC quality environment. The objective of the U.S. Department of Energy (DOE) Office of Nuclear Energy Advanced Modeling and Simulation Nuclear Waste Management Integrated Performance and Safety Codes (NEAMS Nuclear Waste Management IPSC) program element is to provide an integrated suite of computational modeling and simulation (M&S) capabilities to assess quantitatively the long-term performance of waste forms in the engineered and geologic environments of a radioactive-waste storage facility or disposal repository. This objective will be fulfilled by acquiring and developing M&S capabilities, and establishing a defensible level of confidence in these M&S capabilities. The foundation for assessing the level of confidence is based upon the rigor and results from verification, validation, and uncertainty quantification (V&V and UQ) activities. M&S capabilities are to be managed, verified, and validated within the NEAMS Nuclear Waste Management IPSC quality environment. M&S capabilities and the supporting analysis workflow and simulation data management tools will be distributed to end-users from this same quality environment. The same analysis workflow and simulation data management tools that are to be distributed to end-users will be used for verification and validation (V&V) activities within the quality environment. This strategic decision reduces the number of tools to be supported, and increases the quality of tools distributed to end users due to rigorous use by V&V activities. NEAMS Nuclear Waste Management IPSC V&V and UQ practices and evidence management goals are documented in the V&V Plan. This V&V plan includes a description of the quality environment into which M&S capabilities are imported and V&V and UQ activities are managed. The first phase of implementing the V&V plan is to deploy an initial quality environment through the acquisition and integration of a set of software tools. An evaluation of the needs, options, and tools selected for the quality environment is given in this report.

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Results 68801–69000 of 99,299
Results 68801–69000 of 99,299