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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 1,405 records · Page 78
All sourcesNASA NTRSDOE OSTI
DOE OSTI2015

Role of neutral gas in scrape-off layer tokamak plasma

Neutral gas in scrape-off layer of tokamak plasma plays an important role as it can modify the plasma turbulence. In order to investigate this, we have derived a simple two-dimensional (2D) model that consists of electron continuity, quasi-neutrality, and neutral gas continuity equations using neutral gas ionization and charge exchange processes. Simple 1D profile analysis predicts neutral penetration depth into the plasma. Growth rate obtained from the linear theory has been presented. The 2D model equations have been solved numerically. It is found that the neutral gas reduces plasma fluctuations and shifts spectrum of the turbulence towards lower frequency side. The neutral gas fluctuation levels have been presented. The numerical results have been compared with Aditya tokamak experiments.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2017

Investigations of effect of phase change mass transfer rate on cavitation process with homogeneous relaxation model

The super high fuel injection pressure and micro size of nozzle orifice has been an important development trend for the fuel injection system. Accordingly, cavitation transient process, fuel compressibility, amount of noncondensable gas in the fuel and cavitation erosion have attracted more attention. Based on the fact of cavitation in itself is a kind of thermodynamic phase change process, this paper takes the perspective of the cavitation phase change mass transfer process to analyze above mentioned phenomenon. The two-phase cavitating turbulent flow simulations with VOF approach coupled with HRM cavitation model and U-RANS of standard k-ε turbulence model were performed for investigations of cavitation phase change mass transfer process. It is concluded the mass transfer time scale coefficient in the Homogenous Relaxation Model (HRM) representing mass transfer rate should tend to be as small as possible in a condition that ensured the solver stable. At very fast mass transfer rate, the phase change occurs at very thin interface between liquid and vapor phase and condensation occurs more focused and then will contribute predictably to a more serious cavitation erosion. Both the initial non-condensable gas in fuel and the fuel compressibility can accelerate the cavitation mass transfer process.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2020

A global anthropogenic emission inventory of atmospheric pollutants from sector- and fuel-specific sources (1970–2017): an application of the Community Emissions Data System (CEDS)

Global anthropogenic emission inventories remain vital for understanding the sources of atmospheric pollution and the associated impacts on the environment, human health, and society. Rapid changes in today's society require that these inventories provide contemporary estimates of multiple atmospheric pollutants with both source sector and fuel type information to understand and effectively mitigate future impacts. To fill this need, we have updated the open-source Community Emissions Data System (CEDS) (Hoesly et al., 2019) to develop a new global emission inventory, CEDSGBD-MAPS. This inventory includes emissions of seven key atmospheric pollutants (NOx; CO; SO2; NH3; non-methane volatile organic compounds, NMVOCs; black carbon, BC; organic carbon, OC) over the time period from 1970–2017 and reports annual country-total emissions as a function of 11 anthropogenic sectors (agriculture; energy generation; industrial processes; on-road and non-road transportation; separate residential, commercial, and other sectors (RCO); waste; solvent use; and international shipping) and four fuel categories (total coal, solid biofuel, the sum of liquid-fuel and natural-gas combustion, and remaining process-level emissions). The CEDSGBD-MAPS inventory additionally includes monthly global gridded (0.5°?×?0.5°) emission fluxes for each compound, sector, and fuel type to facilitate their use in earth system models. CEDSGBD-MAPS utilizes updated activity data, updates to the core CEDS default scaling procedure, and modifications to the final procedures for emissions gridding and aggregation. Relative to the previous CEDS inventory (Hoesly et al., 2018), these updates extend the emission estimates from 2014 to 2017 and improve the overall agreement between CEDS and two widely used global bottom-up emission inventories. The CEDSGBD-MAPS inventory provides the most contemporary global emission estimates to date for these key atmospheric pollutants and is the first to provide global estimates for these species as a function of multiple fuel types and source sectors. Dominant sources of global NOx and SO2 emissions in 2017 include the combustion of oil, gas, and coal in the energy and industry sectors as well as on-road transportation and international shipping for NOx. Dominant sources of global CO emissions in 2017 include on-road transportation and residential biofuel combustion. Dominant global sources of carbonaceous aerosol in 2017 include residential biofuel combustion, on-road transportation (BC only), and emissions from the waste sector. Global emissions of NOx, SO2, CO, BC, and OC all peak in 2012 or earlier, with more recent emission reductions driven by large changes in emissions from China, North America, and Europe. In contrast, global emissions of NH3 and NMVOCs continuously increase between 1970 and 2017, with agriculture as a major source of global NH3 emissions and solvent use, energy, residential, and the on-road transport sectors as major sources of global NMVOCs. Due to similar development methods and underlying datasets, the CEDSGBD-MAPS emissions are expected to have consistent sources of uncertainty as other bottom-up inventories. The CEDSGBD-MAPS source code is publicly available online through GitHub: https://github.com/emcduffie/CEDS/tree/CEDS_GBD-MAPS (last access: 1 December 2020). The CEDSGBD-MAPS emission inventory dataset (both annual country-total and monthly global gridded files) is publicly available under https://doi.org/10.5281/zenodo.3754964 (McDuffie et al., 2020c).

Mcduffie, Erin↗
DOE OSTI2017

NiAl Oxidation Reaction Processes Studied In Situ Using MEMS-Based Closed-Cell Gas Reaction Transmission Electron Microscopy

The nanoscale oxidation mechanisms and kinetics of a model β-NiAl system were investigated using in situ closed-cell gas reaction scanning transmission electron microscopy (STEM). Here, we directly visualize the dynamic structural and chemical changes that occur during high-temperature oxidation at a high spatial resolution of 50.3Ni–49.7Al (at.%) nanoparticles under static air conditions at 730 Torr with heating up to 750 °C at 5 °C/s. A MEMS-based gas cell system, with microfabricated heater devices and a gas delivery system, was used to reveal site-specific oxidation initiation sites. Through time-resolved annular dark-field STEM imaging, we tracked the nanoscale oxidation kinetics of Al 2 O 3 . After oxidation at 750 °C, nucleation of voids at the Ni/Al 2 O 3 interface was observed along a NiAl grain boundary, followed by the formation of faceted NiO crystals. Small faceted cubic crystals of NiO were formed at the initial stage of oxidation at high PO 2 due to the outward self-diffusion of Ni 2+ ions, followed by the formation of a mixture of metastable and stable α-Al 2 O 3 at the oxide/metal interface that is attributed to a PO 2 decrease with oxidation time, which agreed with thermodynamic modeling calculations. Furthermore, the results from these in situ oxidation experiments in the β-NiAl system are in agreement with the established oxidation mechanisms; however, with in situ closed-cell gas microscopy it is now feasible to investigate nanoscale oxidation mechanisms and kinetics in real time and at high spatial resolution and can be broadly applied to understand the basic high-temperature oxidation mechanisms for a wide range of alloy compositions.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Ecton processes in the generation of pulsed runaway electron beams in a gas discharge

As was shown earlier for pulsed discharges that occur in electric fields rising with extremely high rates (10{sup 18} V/(cm s)) during the pulse rise time, the electron current in a vacuum discharge is lower than the current of runaway electrons in an atmospheric air discharge in a 1-cm-long gap. In this paper, this is explained by that the field emission current from cathode microprotrusions in a gas discharge is enhanced due to gas ionization. This hastens the initiation of explosive electron emission, which occurs within 10{sup –11} s at a current density of up to 10{sup 10} A/cm{sup 2}. Thereafter, a first-type cathode spot starts forming. The temperature of the cathode spot decreases due to heat conduction, and the explosive emission current ceases. Thus, the runaway electron current pulse is similar in nature to the ecton phenomenon in a vacuum discharge.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2012

Lift-off patterning processes employing energetically-stimulated local removal of solid-condensed-gas layers

The invention provides a method for forming a patterned material layer on a structure, by condensing a vapor to a solid condensate layer on a surface of the structure and then localized removal of selected regions of the condensate layer by directing an ion beam at the selected regions, exposing the structure at the selected regions. A material layer is then deposited on top of the solid condensate layer and the exposed structure at the selected regions. Then the solid condensate layer and regions of the material layer that were deposited on the solid condensate layer are removed, leaving a patterned material layer on the structure.

Branton, Daniel↗
DOE OSTI2017

Effect of Recrystallization on Gas Bubble Swelling in UMo Fuels

The development of low-enriched uranium (LEU) fuels such as UMo dispersion fuels and monolithic UMo fuels is part of a global effort on nuclear nonproliferation. Although UMo fuels have the advantage of high density, excellent irradiation performance and good thermal conductivity, the volumetric swelling in irradiated metallic fuels is known to be an important design parameter because it affects not only the thermal conductivity of the fuels but also the mechanical integrity of fuel structures. Experiments also show that recrystallization dramatically affects the gas bubble swelling kinetics. A series of materials processes such as casting, mechanical rolling and thermal treatment are used in fuel fabrication. Resulting microstructure, such as grain size, porosity, and second phase, strongly depends on the material processes and process parameters. Therefore, a fundamental understanding how fabricated microstructures and irradiation conditions affect the nucleation of gas bubbles, recrystallization and gas bubble swelling kinetics is essential for optimizing material processes to obtain desired microstructure and fuel performance. Great effort has been made in the development of modeling capability for predicting gas bubble swelling kinetics and fission gas release kinetics in nuclear fuels. However, these models are based on the assumptions that the inter- and intra-granular gas bubble sizes are independent of position and only depend on time or fission density. Therefore, they are applicable to a material with uniform microstructure such as equiaxed grains with homogeneous defect distributions, homogeneous thermodynamic and kinetic properties of defects, and uniform radiation conditions. Very recently, we developed a three dimension (3D) microstructure dependent gas bubble swelling model for investigating the effect of heterogeneous microstructures and inhomogeneous thermodynamic properties of defects on gas bubble swelling in polycrystalline UMo fuels. However, the model doesn't take into account the effect of recrystallization on swelling kinetics. In this work, the spatially dependent rate theory is used to describe the evolution of interstitials and interstitial loop density. Recrystallization is described by a phase-field model with a concept of 'phase transition' when the local interstitial loop density is larger than a critical value. The intra- and inter- granular gas bubble evolution is described by the spatially dependent Booth model. A model integrating all the microstructure evolution enables one to study the effect of heterogeneous microstructures, recrystallization, and the metallic fuel thermodynamic and kinetic properties on gas bubble swelling kinetics.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2025

Non-Equilibrium in a Dust-Forming Low-Temperature Plasma: A CARS Study

Dust-forming low-temperature plasmas are versatile systems for the production of nanoparticles with tunable functionalities. While attractive from a materials processing point of view, these systems are inherently complex, with several plasma-induced phenomena determining the properties of the produced materials. Here, we characterize a carbon nanoparticle-forming plasma using coherent anti-Stokes Raman spectroscopy (CARS), with the primary goal of measuring gas temperature. While gas temperature is typically assumed to be at or slightly above room temperature in these reactors, we measure gas temperatures exceeding 1000 K under typical process conditions. We find a correlation between the gas temperature and the nanoparticle yield, suggesting that the particle nucleation and growth process releases energy within the reaction volume, leading to significant gas heating. In addition, we find that the relaxation of vibrationally excited species at the particle surfaces is a major contributor to their heating. In conclusion, these results underscore the complexity of these systems and the need for their more in-depth characterization using advanced techniques such as CARS.

Basic Plasma Phenomena and Gas Discharges↗
DOE OSTI2016

Life Extension of Nuclear Plant Facilities through Monitoring and Detailed Analysis - 16175

The UK has accumulated a substantial legacy of radioactive waste from various civil nuclear and defence programmes. Presently, however most of the UK radioactive waste is generated from nine power stations which generate approximately one sixth of the of the country's electricity. Irradiated fuel is removed from these reactors and safe management of the radioactive solid and liquid effluents is required. The safe management of these effluents is essential. Sellafield, in West Cumbria UK, contains two reprocessing plants, one designed to process nuclear fuel from Magnox reactors (CO{sub 2} cooled with Uranium bar fuel) and the other to process nuclear fuel from Advanced Gas cooled Reactors and Pressurized Water Reactors. The reprocessing stage enables extraction of fissile material for recycling. This leaves a volume of dilute but high-level waste. The high-level radioactive liquid waste is concentrated to reduce its volume and then incorporated into borosilicate glass, using a process called vitrification. The glass is then poured into stainless steel containers and placed in long term storage. This required concentration of HLW liquor is achieved using a suite of aging evaporators. All evaporators are of similar design constructed from corrosion resistant stainless steel having dimensions height ∼11 m, internal diameter 3.05 m and capable of holding 13.7 m{sup 3} of liquor. The basic principle of operation is to heat the dilute liquor under partial vacuum, at constant volume, until the target concentration is achieved. Heating of the liquor is achieved using steam heated coils within the evaporator, and steam in the jacket which surrounds the lower half of the evaporator vessel. The evaporator is then brought to atmospheric pressure and the concentrated liquor is ejected whilst hot. The evaporator is then cooled with water cooled coils and a water filled jacket. New dilute liquor is then added for a new batch. The process is then repeated. As the evaporators reach the end of their original design life accurate prediction of the current condition of nuclear plant facilities is essential to safely justify continued plant operation by ensuring structural integrity. This poses a significant challenge as many aging UK nuclear facilities were not inherently built with inspection in mind. The potential life limiting components of the HA evaporators at Sellafield are the surfaces that contact the product liquor at elevated temperatures i.e. the steam heated surfaces of the coils within the evaporator vessel and the vessel base and wall surrounded by the steam jacket. Each heating component is critical to the operational life of the evaporator - the removal from service of a coil heating component significantly reduces the operational flexibility and remnant life of this plant. Over the last decade a variety of cutting-edge expertise and methodologies have been utilised to accurately measure and then predict the current condition of the plant and also to predict its remnant life. This paper provides an overview of the development of several techniques deployed, namely non-destructive testing/inspection, in-house software development and finite element modelling. These methods have been validated by lab-scale or full-scale experiments along with historical plant data. These techniques have been evolved and refined for over a decade, providing vital insights into the physical behaviour of this complex reprocessing system. This enables not only accurate assessment of the current condition of the plant equipment but also allows scientifically underpinned predictions to be made of how it will behave into the future. This is critical for Sellafield as this knowledge feeds into their safety case to the Office of Nuclear Regulation to justify continued operation. It is concluded that this integrated approach provides a robust analysis tool which has driven change and optimisation of plant procedures ensuring continued safe operation whilst extending the life of the facility. (authors)

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
DOE OSTI2015

A theoretical model of a thinning current sheet in the low-β plasmas

Magnetic reconnection is an important physical process in various explosive phenomena in the universe. In previous studies, it was found that fast reconnection takes place when the thickness of a current sheet becomes on the order of a microscopic length such as the ion Larmor radius or the ion inertial length. In this study, we investigated the pinching process of a current sheet by the Lorentz force in a low-β plasma using one-dimensional magnetohydrodynamics (MHD) simulations. It is known that there is an exact self-similar solution for this problem that neglects gas pressure. We compared the non-linear MHD dynamics with the analytic self-similar solution. From the MHD simulations, we found that with the gas pressure included the implosion process deviates from the analytic self-similar solution as t→t{sub 0}, where t{sub 0} is the explosion time when the thickness of a current sheet of the analytic solution becomes 0. We also found that a pair of MHD fast-mode shocks is generated and propagates after the formation of the pinched current sheet as t→t{sub 0}. On the basis of the Rankine–Hugoniot relations, we derived the scaling law of the physical quantities with respect to the initial plasma beta in the pinched current sheet. Our study could help us estimate the physical quantities in the pinched current sheet formed in a low-β plasma.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2016

Linking pore-scale and basin-scale effects on diffusive methane transport in hydrate bearing environments through multi-scale reservoir simulations

We explore the gas hydrate-generating capacity of diffusive methane transport induced by solubility gradients due to pore size contrasts in lithologically heterogeneous marine sediments. Through the use of 1D, 2D, and 3D reactive transport simulations, we investigate scale-dependent processes in diffusion-dominated gas hydrate systems. These simulations all track a sand body, or series of sands, surrounded by clays as they are buried through the gas hydrate stability zone. Methane is sourced by microbial methanogenesis in the clays surrounding the sand layers. In 1D, simulations performed in a Lagrangian reference frame demonstrate that gas hydrate in thin sands (3.6 m thick) can occur in high saturations (upward of 70%) at the edges of sand bodies within the upper 400 meters below the seafloor. Diffusion of methane toward the center of the sand layer depends on the concentration gradient within the sand: broader sand pore size distributions with smaller median pore sizes enhance diffusive action toward the sand’s center. Incorporating downhole log- and laboratory-derived sand pore size distributions, gas hydrate saturations in the center of the sand can reach 20% of the hydrate saturations at the sand’s edges. Furthermore, we show that hydrate-free zones exist immediately above and below the sand and are approximately 5 m thick, depending on the sand-clay solubility contrast. A moving reference frame is also adopted in 2D, and the angle of gravity is rotated relative to the grid system to simulate a dipping sand layer. This is important to minimize diffusive edge effects or numerical diffusion that might be associated with a dipping sand in an Eulerian grid system oriented orthogonal to gravity. Two-dimensional simulations demonstrate the tendency for gas hydrate to accumulate downdip in a sand body because of greater methane transport at depth due to larger sand-clay solubility contrasts. In 3D, basin-scale simulations illuminate how convergent sand layers in a multilayered system can compete for diffusion from clays between them, resulting in relatively low hydrate saturations. All simulations suggest that when hydrate present in clays dissociates with burial, the additional dissolved methane is soaked up by nearby sands preserving high hydrate saturations.

Nole, Michael↗
DOE OSTI2017

Thermal Feedback in the High-mass Star- and Cluster-forming Region W51

High-mass stars have generally been assumed to accrete most of their mass while already contracted onto the main sequence, but this hypothesis has not been observationally tested. We present ALMA observations of a 3×1.5 pc area in the W51 high-mass star-forming complex. We identify dust continuum sources and measure the gas and dust temperature through both rotational diagram modeling of CH{sub 3}OH and brightness-temperature-based limits. The observed region contains three high-mass YSOs that appear to be at the earliest stages of their formation, with no signs of ionizing radiation from their central sources. The data reveal high gas and dust temperatures (T>100 K) extending out to about 5000 au from each of these sources. There are no clear signs of disks or rotating structures down to our 1000 au resolution. The extended warm gas provides evidence that, during the process of forming, these high-mass stars heat a large volume and correspondingly large mass of gas in their surroundings, inhibiting fragmentation and therefore keeping a large reservoir available to feed from. By contrast, the more mature massive stars that illuminate compact H II regions have little effect on their surrounding dense gas, suggesting that these main-sequence stars have completed most or all of their accretion. The high luminosity of the massive protostars (L>10{sup 4} L{sub ⊙}), combined with a lack of centimeter continuum emission from these sources, implies that they are not on the main sequence while they accrete the majority of their mass; instead, they may be bloated and cool.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2011

Modelling of Ion Cyclotron Wall Conditioning plasmas

Ion Cyclotron Wall Conditioning (ICWC) is envisioned in ITER to clean the wall from impurities, to control the wall isotopic ratio and the hydrogen recycling in the presence of the toroidal magnetic field. Various experiments and modelling are advancing to consolidate this technique. In this contribution the modeling of ICWC is presented, which can be divided in two parts: plasma description and plasma wall interaction. Firstly a 0D plasma model, based on a set of energy and particle balance equations for Maxwellian Hydrogen and Helium species, is presented. The model takes into account elementary collision processes, coupled RF power, particle confinement, wall recycling, and active gas injection and pumping. The RF plasma production process is based mainly on electron collisional ionization. The dependency of the plasma parameters, the Hydrogen and Helium partial pressures and neutral or ionic fluxes on pressure and RF power are quantitatively in good agreement with those obtained experimentally on TORE SUPRA. Secondly an extension of the 0D model including the description of the wall interaction is presented and compared to TORE SUPRA multi-pulse ICWC discharges.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2013

Pilot Scale Integrated Biorefinery for Producing Ethanol from Hybrid Algae (CRADA Final Report)

This collaboration between Algenol Biofuels Inc. and NREL will provide valuable information regarding Direct to Ethanol technology. Specifically, the cooperative R&D will analyze the use of flue gas from industrial sources in the Direct to Ethanol process, which may demonstrate the potential to significantly reduce greenhouse gas emissions while simultaneously producing a valuable product, i.e., ethanol. Additionally, Algenol Biofuels Inc. and NREL will develop both a techno-economic model with full material and energy balances and an updated life-cycle analysis to identify greenhouse gas emissions relative to gasoline, each of which will provide a better understanding of the Direct to Ethanol process and further demonstrate that it is a breakthrough technology with varied and significant benefits.

09 BIOMASS FUELS↗
DOE OSTI2018

Renewable Energy Center

The major goal of this project is to develop an efficient gasification system in order to convert woody biomass and agricultural residue from North Carolina to synthesis gas (syngas). Then, convert syngas into liquid fuel through catalytic process and to heat and power through a gas turbine.

09 BIOMASS FUELS↗