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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 181 records · Page 10
All sourcesNASA NTRSDOE OSTI
NASA NTRS1995

Estimating the urban bias of surface shelter temperatures using upper-air and satellite data. Part 1: Development of models predicting surface shelter temperatures

Multiple regression techniques were used to predict surface shelter temperatures based on the time period 1986-89 using upper-air data from the European Centre for Medium-Range Weather Forecasts (ECMWF) to represent the background climate and site-specific data to represent the local landscape. Global monthly mean temperature models were developed using data from over 5000 stations available in the Global Historical Climate Network (GHCN). Monthly maximum, mean, and minimum temperature models for the United States were also developed using data from over 1000 stations available in the U.S. Cooperative (COOP) Network and comparative monthly mean temperature models were developed using over 1150 U.S. stations in the GHCN. Three-, six-, and full-variable models were developed for comparative purposes. Inferences about the variables selected for the various models were easier for the GHCN models, which displayed month-to-month consistency in which variables were selected, than for the COOP models, which were assigned a different list of variables for nearly every month. These and other results suggest that global calibration is preferred because data from the global spectrum of physical processes that control surface temperatures are incorporated in a global model. All of the models that were developed in this study validated relatively well, especially the global models. Recalibration of the models with validation data resulted in only slightly poorer regression statistics, indicating that the calibration list of variables was valid. Predictions using data from the validation dataset in the calibrated equation were better for the GHCN models, and the globally calibrated GHCN models generally provided better U.S. predictions than the U.S.-calibrated COOP models. Overall, the GHCN and COOP models explained approximately 64%-95% of the total variance of surface shelter temperatures, depending on the month and the number of model variables. In addition, root-mean-square errors (rmse's) were over 3 C for GHCN models and over 2 C for COOP models for winter months, and near 2 C for GHCN models and near 1.5 C for COOP models for summer months.

Epperson, David L.↗
NASA NTRS1991

Monte Carlo simulation of nonequilibrium shock fronts

A direct simulation of a shock-tube experiment carried by AVCO (pressure of 1 Torr and velocity of 6.4 km/sec), repeated by Sharma and Gillespie (1990), and used by Park (1988) to develop his two-temperature model, is presented. Results show that the electronic ground state of N2 is not in rotational nor vibrational equilibrium with that of N2(+). Moreover, a two-temperature model is inadequate to describe nonequilibrium flows behind shocks. The role of impurities is examined. It is shown that the effects of a small fraction of H2O are insignificant. Good agreement with the measurements of Sharma and Gillespie is indicated.

Olynick, David P.↗
DOE OSTI2015

Plasma viscosity with mass transport in spherical inertial confinement fusion implosion simulations

The effects of viscosity and small-scale atomic-level mixing on plasmas in inertial confinement fusion(ICF) currently represent challenges in ICF research. Many current ICF hydrodynamic codes ignore the effects of viscosity though recent research indicates viscosity and mixing by classical transport processes may have a substantial impact on implosion dynamics. In this paper, we have implemented a Lagrangian hydrodynamic code in one-dimensional spherical geometry with plasmaviscosity and mass transport and including a three temperature model for ions, electrons, and radiation treated in a gray radiation diffusion approximation. The code is used to study ICF implosion differences with and without plasmaviscosity and to determine the impacts of viscosity on temperature histories and neutron yield. It was found that plasmaviscosity has substantial impacts on ICF shock dynamics characterized by shock burn timing, maximum burn temperatures, convergence ratio, and time history of neutron production rates. Finally, plasmaviscosity reduces the need for artificial viscosity to maintain numerical stability in the Lagrangian formulation and also modifies the flux-limiting needed for electron thermal conduction.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2025

Toward model-free temperature diagnostics of warm dense matter from multiple scattering angles

Warm dense matter plays an important role in astrophysical objects and technological applications, but the rigorous diagnostics of corresponding experiments is notoriously difficult. In this work, we present a model-free analysis of x-ray Thomson scattering (XRTS) measurements on isochorically heated graphite obtained at the Linac Coherent Light Source at multiple scattering angles. We demonstrate that the recent imaginary-time thermometry technique works for scattering data that have been measured in both forward and backward scattering geometry. This opens up the way toward a rigorous quantification of nonequilibrium effects in future experiments, where XRTS measurements are being obtained from multiple scattering angles from the same sample.

Equations of state↗
NASA NTRS1991

High temperature furnace modeling and performance verifications

A two dimensional conduction/radiation problem for an alumina crucible in a zirconia heater/muffle tube enclosing a liquid iron sample was solved numerically. Variations in the crucible wall thickness were numerically examined. The results showed that the temperature profiles within the liquid iron sample were significantly affected by the crucible wall thicknesses. New zirconia heating elements are under development that will permit continued experimental investigations of the zirconia furnace. These elements have been designed to work with the existing furnace and have been shown to have longer lifetimes than commercially available zirconia heating elements. The first element has been constructed and tested successfully.

Smith, James E., Jr.↗
NASA NTRS1989

Coronal activity in F-, G-, and K-type stars. III - The coronal differential emission measure distribution of Capella, Sigma-squared CrB, and Procyon

EXOSAT soft X-ray spectra of three binary systems of cool stars are analyzed: Capella (G6 III + F9 III), Sigma-squared CrB (F8 V + G1 V), and Procyon (F5 IV-V + DF). The EXOSAT transmission grating spectrometer permits the study of individual spectral lines and line complexes between 10 and 200 A with approximately 3 A resolution. First it is demonstrated that the spectra can be described reasonably well by a two-temperature model corona. Then the assumption that only two temperatures exist in the stellar coronas is relaxed and differential emission measure distributions are derived from the three spectra. The results from the multithermal modeling are consistent with those of the two-temperature models: emission from the coronas of each of the three stars is dominated by plasma in two relative narrow temperature intervals. These intervals are centered on 5 MK and 25 MK in the cases of Capella and Sigma-squared CrB, and 0.6 MK and 3 MK in the case of Procyon. The implications of the results for the structure of stellar coronas are briefly discussed.

Lemen, J. R.↗
DOE OSTI2017

Eigendecomposition model of resistance temperature detector with applications to S-CO 2 cycle sensing

Super-critical carbon dioxide (S-CO2) is a promising thermodynamic cycle for advanced nuclear reactors and solar energy conversion applications. Dynamic control of the proposed recompression S-CO2 cycle is accomplished with input from resistance temperature detector (RTD) measurements of the process fluid. One of the challenges in practical implementation of S-CO2 cycle is high corrosion rate of component and sensor materials. In this paper, we develop a mathematical model of RTD sensing using eigendecomposition model of radial heat transfer in a layered long cylinder. We show that the value of RTD time constant primarily depends on the rate of heat transfer from the fluid to the outer wall of RTD. We also show that for typical material properties, RTD time constant can be calculated as the sum of reciprocal eigen-values of the heat transfer matrix. Using the computational model and a set of RTD and CO2 fluid thermophysical parameter values, we calculate the value of time constant of thermowell-mounted RTD sensor at the hot side of the precooler in the S-CO2 cycle. The eigendecomposition model of RTD will be used in future studies to model sensor degradation and its impact on control of S-CO2. (C) 2016 Elsevier B.V. All rights reserved.

finite element↗
DOE OSTI2023

High temperature creep model development using in-situ 3-D DIC techniques during a simulated LOCA transient

In-situ strain measurements of fuel cladding can enable high-throughput data collection and validation to support accelerated qualification of cladding materials. Here, in this work, 3D digital image correlation was used to map strain for both Zircaloy-4 (Zry-4) and Cr-coated Zry-4 during two types of cladding rupture experiments: isobaric temperature ramp tests at 5 °C/s and isothermal pressure jump tests at 600 °C. Zry-4 strain data initially showed a temperature dependence expected for creep deformation, yet a shift to a new plastic deformation mechanism not reported in literature dominated during the finals seconds prior to rupture. Cr-coated Zry-4 did not show the change in deformation mechanism at the end of life and showed a delay in measurable creep deformation. Stress dependences were similar for Zry-4 and Cr/Zry-4 during pressure jump tests. Cr-coatings were found to decrease the strain rate during both testing scenarios. Creep parameters were calculated to support modelling efforts regarding design basis accidents.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Characterizing the nonequilibrium response of FeRh thin films using time-domain thermoreflectance

Time-domain thermoreflectance (TDTR) characterization of FeRh throughout its first-order antiferromagnetic (AF) to ferromagnetic (FM) transition shows that the transient reflectance ΔR⁡(t)/R strongly depends on the magnetic order of the sample. Using TDTR, which uses optical pulses to induce small temperature excursions, we have found that Δ⁢R⁡(t)/R of the AF phase exhibits a large negative response, while the response of the FM phase is positive. This magnetic phase sensitivity has allowed us to study the transient response of both the AF and FM phases to the pump-pulse excitation and the mixed phase of the material. These results are significant since the ultrafast properties of antiferromagnetic materials and mixed antiferromagnetic and ferromagnetic materials are difficult to detect using other conventional techniques. We have found that the AF phase exhibits a strong subpicosecond decaying signal not observed in the FM phase. The magnetic phase dependence of the sign of Δ⁢R⁡(t)/R is qualitatively explained using the results of ab initio density functional theory calculations. Using the two-temperature model, we found that the change in the thermalization time across the transition is caused by differences in both the electronic heat capacity and the electron-phonon coupling factor of the AF and FM phases. The electron-phonon coupling constant in the AF phase is also determined using the two-temperature model conducted using the ntmpy code package. For the FM phase, we provide boundaries for the magnitude of the electron-phonon coupling factor for the FM phase. Finally, these results indicate that TDTR can be used to study the transient properties of magnetic materials that are otherwise challenging to probe.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
NASA NTRS1979

Apollo-Soyuz survey of the extreme-ultraviolet/soft X-ray background

The paper reports results of the most extensive survey to date of the EUV/soft X-ray background, obtained with an EUV telescope on the Apollo-Soyuz mission. The principal results may be summarized as follows: (1) an intense background flux exists down to energies of 100 eV (4.0 plus or minus 1.3 photons/sq cm/sec/sr/eV average diffuse flux); (2) the Apollo-Soyuz data alone places lower and upper limits on single-temperature models for EUV-emitting interstellar gas for the log T range of 5.1-6.0; and (3) the allowed range would have to be restricted to log T of 5.1-5.6 for the Cash, Malina, and Stern (1976), Burstein et al. (1977), and Apollo-Soyuz data sets to satisfy a single-temperature model for the background at not greater than 280 eV.

Stern, R.↗
DOE OSTI2019

Ultrafast quasiparticle dynamics in the correlated semimetal Ca 3 Ru 2 O 7

The correlated polar semimetal Ca 3 Ru 2 O 7 exhibits a rich phase diagram including two magnetic transitions (T N = 56 K and T C = 48 K) with the appearance of an insulating-like pseudogap (at T C ). In addition, there is a crossover back to metallic behavior at T* = 30 K, the origin of which is still under debate. We utilized ultrafast optical-pump optical-probe spectroscopy to investigate quasiparticle dynamics as a function of temperature in this enigmatic quantum material. We identify two dynamical processes, both of which are influenced by the onset of the pseudogap. This includes electron-phonon relaxation and, below T C , the onset of a phonon bottleneck hindering the relaxation of quasiparticles across the pseudogap. We introduce a gap-modified two-temperature model to describe the temperature dependence of electron-phonon thermalization, and use the Rothwarf-Taylor to model the phonon bottleneck. In conjunction with density functional theory, our experimental results synergistically reveal the origin of the T-dependent pseudogap. Further, our data and analysis indicate that T* emerges as a natural consequence of T-dependent gapping out of carriers, and does not correspond to a separate electronic transition. Furthermore, our results highlight the value of low-fluence ultrafast optics as a sensitive probe of low-energy electronic structure, thermodynamic parameters, and transport properties of Ruddlesden-Popper ruthenates.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

High Temperature Viscosity Model For Glassy Slags Produced From The Air Products Municipal Waste Gasification Process

Air Products, Inc. (AP) is developing a technology that uses plasma-enhanced gasification to create syngas from Municipal Solid Waste (MSW), for the purpose of generating electricity at a large scale. The process is intended to convert the inorganic components in MSW to a slag that flows easily through and from the gasifier. AP and the Savannah River National Laboratory (SRNL) have established a Cooperative Research and Development Agreement (CRADA) to improve the properties of the slag material produced from MSW gasification. A primary objective for AP is the development of a viscosity model, which can be used to predict the viscosity of the slag produced in the gasification process as a function of its composition in order to ensure that the incoming feeds will ultimately yield slag that can effectively be poured from the gasifier. In addition, the development of such a model could allow AP to determine the type and amount of additives to mix with the incoming MSW to target a specific viscosity range as well as identify waste compositions that could lead to difficulties during processing.

high temperature↗
NASA NTRS2003

Multiaxial Temperature- and Time-Dependent Failure Model

A temperature- and time-dependent mathematical model predicts the conditions for failure of a material subjected to multiaxial stress. The model was initially applied to a filled epoxy below its glass-transition temperature, and is expected to be applicable to other materials, at least below their glass-transition temperatures. The model is justified simply by the fact that it closely approximates the experimentally observed failure behavior of this material: The multiaxiality of the model has been confirmed (see figure) and the model has been shown to be applicable at temperatures from -20 to 115 F (-29 to 46 C) and to predict tensile failures of constant-load and constant-load-rate specimens with failure times ranging from minutes to months..

Richardson, David↗
DOE OSTI2019

Nonequilibrium Phenomena in (Quasi-)thermal Plasma Flows

Thermal plasmas are utilized in diverse applications that require high power densities or throughputs, such as metal cutting, welding, spraying, metallurgy, and materials synthesis. Thermal plasma applications involve interactions between the highly energetic plasma and working gas streams, confining devices, or processing materials. Whereas thermal plasma implies a state of equilibrium (i.e. Local Thermodynamic Equilibrium, LTE), due to the above interactions, thermal plasma flows depict nonequilibrium phenomena of two types: kinetic and dissipative. Kinetic nonequilibrium manifests microscopically and is caused by localized imbalances between particles and fields interactions. Its occurrence is illustrated, for example, as deviations from thermal equilibrium between heavy-species and electrons or from mass-action laws. In contrast, dissipative nonequilibrium reveals macroscopically and is produced by external driving forces that incite distributed responses, such as the growth of instabilities, the occurrence of self-organization, or the establishment of turbulence. While kinetic nonequilibrium has been increasingly incorporated in thermal plasma flow models (e.g. finite-rate chemistry, two-temperature models), it is the great advances in numerical computing that is enabling the exploration of dissipative nonequilibrium (e.g. pattern formation, small-scale turbulent features). Both types of nonequilibrium are reviewed, including their estimation and incidence, within the context of computational models and their relevance to thermal plasma sources and processes.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
NASA NTRS1978

CIRA 1972, recent atmospheric models, and improvements in progress

The paper reviews current progress in the development of atmospheric models. Consideration is given to CIRA 1972 (COSPAR International Reference Atmosphere), the OGO 6 model (1974), the ESRO 4 model (1977), the global Doppler-temperature model of Thuillier et al. (1977), the Jacchia 1977 model (based on a synthesis of temperature, mass-spectrometer, and total-density data from many sources), and the MSIS model (1977), based on incoherent-scatter temperatures and mass-spectrometer data from various sources. New models of the disturbed thermosphere, developed by the author, are compared with recent mass-spectrometer measurements at 170 km.

Jacchia, L. G.↗