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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 541 records · Page 30
All sourcesNASA NTRSDOE OSTI
DOE OSTI2023

CO Oxidation Catalyzed by Au Dispersed on SBA-15 Modified with TiO2 Films Grown via Atomic Layer Deposition (ALD)

It has been established that gold, when in nanoparticle (NP) form and in contact with reducible oxides, can promote oxidation reactions under mild conditions. Here, we report results from our exploration of the catalytic oxidation of carbon monoxide using catalysts where Au NPs were combined with thin titanium oxide films deposited on SBA-15 using atomic layer deposition (ALD). Both orders of deposition, with TiO2 added either before or after Au dispersion, were tested for two titania film thicknesses amounting to about half and full TiO2 monolayers. The resulting catalysts were characterized using various techniques, mainly electron microscopy and N2 adsorption–desorption isotherms, and the kinetics of the oxidation of CO with O2 were followed using infrared absorption spectroscopy. A synergy between the Au and TiO2 phases as it relates to the bonding and conversion of CO was identified, the tuning of which could be controlled by varying the synthetic parameters. The ALD of TiO2 films proved to be an effective way to maximize the Au-TiO2 interface sites, and with that help with the activation of molecular oxygen.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2023

Amphibian Dispersal Traits Not Impacted by Triclopyr Exposure during the Juvenile Stage

Exposure to agrochemicals can have lethal and sublethal effects on amphibians. Most toxicology studies only examine exposure during the aquatic larval stage. Survival of the juvenile stage is the most important for population persistence and it is critical to understand the potential impacts of exposure during this life stage. We investigated how short-term exposure to triclopyr, an herbicide commonly used in forestry management, might impact several juvenile traits. To determine if juveniles perceived exposure as an environmental stressor, we measured their release of corticosterone. We also examined dispersal traits by measuring foraging and hopping behavior. We found no evidence that exposure negatively impacted these traits or was a stressor. Our results provide a preliminary assessment of the potential impact of triclopyr on juvenile amphibians, but we recommend additional research on the effects of agrochemicals on juvenile amphibians.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2021

Two-Phase Turbulence Statistics from High Fidelity Dispersed Droplet Flow Simulations in a Pressurized Water Reactor (PWR) Sub-Channel with Mixing Vanes

In the dispersed flow film boiling regime (DFFB), which exists under post-LOCA (loss-of-coolant accident) conditions in pressurized water reactors (PWRs), there is a complex interplay between droplet dynamics and turbulence in the surrounding steam. Experiments have accredited particular significance to droplet collision with the spacer-grids and mixing vane structures and their consequent positive feedback to the heat transfer recorded in the immediate downstream vicinity. Enabled by high-performance computing (HPC) systems and a massively parallel finite element-based flow solver—PHASTA (Parallel Hierarchic Adaptive Stabilized Transient Analysis)—this work presents high fidelity interface capturing, two-phase, adiabatic simulations in a PWR sub-channel with spacer grids and mixing vanes. Selected flow conditions for the simulations are informed by the experimental data found in the literature, including the steam Reynolds number and collision Weber number (Wec={40,80}), and are characteristic of the DFFB regime. Data were collected from the simulations at an unprecedented resolution, which provides detailed insights into the continuous phase turbulence statistics, highlighting the effects of the presence of droplets and the comparative effect of different Weber numbers on turbulence in the surrounding steam. Further, axial evolution of droplet dynamics was analyzed through cross-sectionally averaged quantities, including droplet volume, surface area and Sauter mean diameter (SMD). The downstream SMD values agree well with the existing empirical correlations for the selected range of Wec. The high-resolution data repository from the simulations herein is expected to be of significance to guide model development for system-level thermal hydraulic codes.

Saini, Nadish↗
DOE OSTI2022

Synthesis of Nano-Oxide Precipitates by Implantation of Ti, Y and O Ions in Fe-10%Cr: Towards an Understanding of Precipitation in Oxide Dispersion-Strengthened (ODS) Steels

The properties of oxide dispersion-strengthened steels are highly dependent on the nature and size distribution of their constituting nano-oxide precipitates. A fine control of the processes of synthesis would enable the optimization of pertinent properties for use in various energy systems. This control, however, requires knowledge of the precise mechanisms of nucleation and growth of the nanoprecipitates, which are still a matter of debate. In the present study, nano-oxide precipitates were produced via the implantation of Y, Ti, and O ions in two different sequential orders in an Fe-10%Cr matrix that was subsequently thermally annealed. The results show that the oxides that precipitate are not necessarily favoured thermodynamically, but rather result from complex kinetics aspects related to the interaction between the implanted elements and induced defects. When Y is implanted first, the formation of nanoprecipitates with characteristics similar to those in conventionally produced ODS steels, especially with a core/shell structure, is evidenced. In contrast, when implantation starts with Ti, the precipitation of yttria during subsequent high-temperature annealing is totally suppressed, and corundum Cr 2 O 3 precipitates instead. Moreover, the systematic involvement of {110} matrix planes in orientation relationships with the precipitates, independently of the precipitate nature, suggests matrix restriction effects on the early stages of precipitation.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Multiscale Modeling of Nanoparticle Precipitation in Oxide Dispersion-Strengthened Steels Produced by Laser Powder Bed Fusion

Laser Powder Bed Fusion (LPBF) enables the efficient production of near-net-shape oxide dispersion-strengthened (ODS) alloys, which possess superior mechanical properties due to oxide nanoparticles (e.g., yttrium oxide, Y-O, and yttrium-titanium oxide, Y-Ti-O) embedded in the alloy matrix. To better understand the precipitation mechanisms of the oxide nanoparticles and predict their size distribution under LPBF conditions, we developed an innovative physics-based multiscale modeling strategy that incorporates multiple computational approaches. These include a finite volume method model (Flow3D) to analyze the temperature field and cooling rate of the melt pool during the LPBF process, a density functional theory model to calculate the binding energy of Y-O particles and the temperature-dependent diffusivities of Y and O in molten 316L stainless steel (SS), and a cluster dynamics model to evaluate the kinetic evolution and size distribution of Y-O nanoparticles in as-fabricated 316L SS ODS alloys. The model-predicted particle sizes exhibit good agreement with experimental measurements across various LPBF process parameters, i.e., laser power (110–220 W) and scanning speed (150–900 mm/s), demonstrating the reliability and predictive power of the modeling approach. The multiscale approach can be used to guide the future design of experimental process parameters to control oxide nanoparticle characteristics in LPBF-manufactured ODS alloys. Additionally, our approach introduces a novel strategy for understanding and modeling the thermodynamics and kinetics of precipitation in high-temperature systems, particularly molten alloys.

Wang, Zhengming (ORCID:0000000241627112)↗
DOE OSTI2021

Hierarchical Fractional Advection-Dispersion Equation (FADE) to Quantify Anomalous Transport in River Corridor over a Broad Spectrum of Scales: Theory and Applications

Fractional calculus-based differential equations were found by previous studies to be promising tools in simulating local-scale anomalous diffusion for pollutants transport in natural geological media (geomedia), but efficient models are still needed for simulating anomalous transport over a broad spectrum of scales. This study proposed a hierarchical framework of fractional advection-dispersion equations (FADEs) for modeling pollutants moving in the river corridor at a full spectrum of scales. Applications showed that the fixed-index FADE could model bed sediment and manganese transport in streams at the geomorphologic unit scale, whereas the variable-index FADE well fitted bedload snapshots at the reach scale with spatially varying indices. Further analyses revealed that the selection of the FADEs depended on the scale, type of the geomedium (i.e., riverbed, aquifer, or soil), and the type of available observation dataset (i.e., the tracer snapshot or breakthrough curve (BTC)). When the pollutant BTC was used, a single-index FADE with scale-dependent parameters could fit the data by upscaling anomalous transport without mapping the sub-grid, intermediate multi-index anomalous diffusion. Pollutant transport in geomedia, therefore, may exhibit complex anomalous scaling in space (and/or time), and the identification of the FADE’s index for the reach-scale anomalous transport, which links the geomorphologic unit and watershed scales, is the core for reliable applications of fractional calculus in hydrology.

97 MATHEMATICS AND COMPUTING↗
DOE OSTI2021

The Effect of Spark-Plug Heat Dispersal Range and Exhaust Valve Opening Timing on Cold-Start Emissions and Cycle-to-Cycle Variability

The partnership for advancing combustion engines (PACE) is a US Department of Energy consortium involving multiple national laboratories and includes a goal of addressing key efficiency and emission barriers in light-duty engines fueled with a market-representative E10 gasoline. A major pillar of the initiative is the generation of detailed experimental data and modeling capabilities to understand and predict cold-start behavior. Cold-start, as defined by the time between first engine crank and three-way catalyst light-off, is responsible for a large percentage of NOx, unburned hydrocarbon and particulate matter emissions in light-duty engines. Minimizing emissions during cold-start is a trade-off between achieving faster light-off of the three-way catalyst and engine out emissions during that period. In this study, gaseous and soot emissions were measured at a distance representative of the three-way catalyst position downstream of the engine at a 2 bar net indicated mean effective pressure (NIMEP) steady-state operating condition representative of cold-start. The test matrix included sweeps of ignition timing 15 degrees-before to 10 degrees-after top dead center firing (TDCf) across three different spark-plug heat dispersal ranges (HR). Additionally, the effect of varying exhaust valve opening (EVO) timing on combustion stability and emissions was also studied. Results show that the spark plug HR affects the coefficient of variation (COV) of NIMEP under all cold-start conditions, while the impact on emissions was found to be minimal. At very retarded spark timings, colder spark plugs required higher air and fuel flow to maintain the desired 2bar NIMEP load, but the fraction of fuel energy going into the exhaust was found to be similar for all spark plugs. Finally, retarding exhaust valve timings showed a simultaneous reduction in emissions while increasing the fraction of fuel energy being fed into the exhaust. However, engine COV was also observed to increase with retarded exhaust timings.

42 ENGINEERING↗
DOE OSTI2020

Dispersionless and dispersion-controlled optical dielectric metasurfaces

Metasurfaces comprise an array of pillars in a lattice. The dimensions of the pillars and the spacing are varied to obtain desired optical properties. The dispersionless metasurfaces can focus optical light over a broad wavelength range. Specific dispersion profiles for the metasurfaces can be designed. Gratings can be fabricated having similar properties as the array of pillars. Pillars in the metasurfaces can have different cross-section profiles.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Surrogate isotope-containing materials for emergency response training and Methods of formation and dispersal

Surrogate materials are in the form of solid particles that include surrogate isotopes, namely, short-lived isotopes selected and formed to serve as surrogates for the radioactive materials of a nuclear fallout without including isotopes that are, or that decay to, biologically or environmentally deleterious and persistent isotopes. The surrogate material may be formed using high-purity reactant material and irradiation and separation techniques that enable tailoring of the isotopes and ratios thereof included in the surrogate material, and the surrogate material may be dispersed, e.g., in a training environment, in solid form.

Carney, Kevin P.↗
DOE OSTI2023

Systems, devices, and methods of enhancing carbon fiber dispersion in wet-laid nonwovens

The present subject matter relates to systems, devices, and methods of enhancing carbon fiber dispersion in wet-laid nonwovens. A quantity of fibers is deposited in a medium, and each of one or more stirring elements is moved in a pattern to mechanically agitate the medium. In some embodiments, moving each of the one or more stirring elements includes moving the one or more stirring elements in complementary patterns to induce a chaotic advection current within the medium.

Ghossein, Hicham Kheir↗
DOE OSTI2024

Atomically dispersed platinum-group metal-free catalysts and method for synthesis of the same

Atomically dispersed platinum-group metal-free catalyst and method for synthesizing the same. According to one embodiment, the catalyst is made by a method in which, in a first step, a metal oxide/zeolitic imidazolate frameworks (ZIF) composite is formed by combining (i) nanoparticles of an oxide of at least one of iron, cobalt, nickel, manganese, and copper, (ii) a hydrated zinc salt, and (iii) an imidazole. Then, in a second step, the metal oxide/ZIF composite is thermally activated, i.e., carbonized, to form an M-N—C catalyst. Thereafter, the M-N—C catalyst may be mixed with a quantity of ammonium chloride, and then the M-N—C/NH 4 Cl mixture may be pyrolyzed. The foregoing NH 4 Cl treatment may improve the intrinsic activity of the catalyst. Then, a thin layer of nitrogen-doped carbon may be added to NH 4 Cl-treated M-N—C catalyst by chemical vapor deposition (CVD). Such CVD treatment may improve the stability of the catalyst.

Wu, Gang↗
DOE OSTI2024

Large eddy simulation of particle dispersion analysis in a pressurized reactive fluid–particle system

Pressurized oxy-combustion (POC) is a promising candidate to reduce carbon emissions in power generation. Designing an effective burner plays a vital role in developing new combustion technologies. Because of high pressure, the volumetric fraction of particles in a pressurized oxy-combustor could be higher than that in the conventional combustor, consequently, the particle dynamics in the pressurized vessel need to be evaluated accordingly. Specifically, the present computational work analyzes the pattern of the particle dispersion by extracting the particle mass flow rate and the particle size distribution in the pressurized combustor. A large eddy simulation (LES) with the environment pressure 15-bar and 100 kWth thermal input of fuel particle has been performed. The particle mass flow rates sampled in several cross-section planes strongly fluctuate, indicating the impacts of the flame as well as the gas-phase flow on the particle movement. Animations of the particle-gas flow show that the flow recirculation plays a major role in producing the pulsing phenomenon of the particle mass flow rate.

Li, Lei↗
DOE OSTI2026

Higher-order space-charge stability in anisotropic beams: Vlasov-Poisson derivation, refined dispersion relations, and stability charts

The Hofmann stability chart is used to screen working points in space-charge-dominated linacs. We identify two errors in its published higher-order dispersion relations: missing $(1\mp2\hatη^2/α)$ factors in the third-order $S^4$ coupling residues, and a sign error in the stated isotropic reduction of the fourth-order relation. Both corrections follow from Hofmann's Vlasov-Poisson equations without fitted parameters. They reproduce coherent tune-shift coefficients in the author's later monograph that the printed forms miss by 24% and 127%. Mode-resolved figures from a published application agree with the corrected relations and reject the printed forms, indicating an inconsistency between the 1998 equations and the calculations underlying those tested figures. We quantify the effect on the non-oscillatory stability chart. Inside the adopted $S^2\le10$ comparison domain, printed and corrected forms disagree on 0.73-2.11% of cells, with no preferred direction. Among excluded cells, disagreement reaches 22%, and the printed relation over-predicts instability at every sampled anisotropy. This concentration may help explain why the errors persisted, although it does not establish their historical cause. For PIP-II, the corrected chart flags four of thirty-two evaluable periods, including one on a third-order odd branch missed by a second-order screen. This count covers non-oscillatory modes only and remains conditional on an unresolved factor-five disagreement between two codes on transverse emittance growth.

Pathak, Abhishek [Fermilab] (ORCID:000000021704208↗
DOE OSTI2024

Impact of Iron Species Dispersion on Fe/ZSM–5 Catalyst Performance for Methane Dehydroaromatization (MDA)

Methane dehydroaromatization (MDA) is one of the most promising technologies for directly transforming methane into aromatics. Unlike the extensively investigated Mo/ZSM-5 catalysts, the structure and, consequently, the catalytic activity of Fe/ZSM-5 are markedly influenced by the method of preparation, as shown here. In this study, we prepared 2 % and 4 % Fe/ZSM-5 catalysts via wet impregnation (WI) and incipient wetness impregnation (IWI). Characterizations (XRD, STEM, UV-Vis, NH 3 -TPD and H 2 -TPR) reveal that 2 %Fe-WI mainly possesses isolated or low-polymerized Fe species within zeolite channels, leading to a rapid activation and a higher benzene yield due to the faster reduction to iron suboxides under MDA conditions. In contrast, 2 %Fe-IWI contains bulk iron oxide aggregates, resulting in a slower activation as these aggregates transform into iron carbide through successive reduction and carbonization. Here, a deactivation kinetic study applied to the 2 % catalysts further demonstrates the quantitative relation between Fe site isolation and catalytic activity. Although both 4 % catalysts inevitably form sizable iron oxide clusters and particles due to the high Fe/Al ratio, similar trends are noted, with the WI catalysts exhibiting a shorter induction/activation period and a higher yield of benzene, paralleling observations made with 2 % catalysts.

03 NATURAL GAS↗
DOE OSTI2026

Influence of overhead HVAC and aerosol control strategies on coarse mode particle dispersion and exposure in a full-scale room experiment

Coarse mode respiratory aerosols can carry viral loads over long distances and have very different dynamics than submicron particles, but experimental studies under realistic conditions remain limited. Here, to study the differential impacts on exposure under different mixing conditions, we co-released 7–10 µm particles and carbon dioxide (CO 2 )—which served as an indicator of gas and submicron particle dynamics—in a 158 m 3 room at LBNL's FLEXLAB facility with an overhead heating, ventilation, and air conditioning (HVAC) system. The room was arranged as a distanced meeting then a classroom with eight heated manikins and a researcher. Spatial variability was measured using 16 particle counters and 22–26 CO 2 sensors throughout the space. Conditions included: HVAC off or supply air at 1000-1060 m 3 h -1 at neutral, cooling, or heating temperatures; with and without 20% outdoor air; and added HVAC filtration, portable air cleaners (PACs), or a physical barrier between the speaker and occupants. We found that good mixing via neutral or cooling supply air or use of PACs under heating lowered coarse particle exposure at some locations, but increased exposure for one-quarter to two-thirds of manikins compared to poor mixing under heating. A physical barrier reduced direct transfer of coarse particles during heating, but less during cooling. High spatial variability shows that a single measurement cannot represent occupant exposure. Instantaneous air mixing assumptions overstate the effectiveness of ventilation, HVAC filtration, and upper-room germicidal ultraviolet disinfection for coarse particles, as relatively few particles reach the return grille or upper room under most conditions.

Air mixing↗