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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 469 records · Page 26
All sourcesNASA NTRSDOE OSTI
DOE OSTI2017

Kinetic analysis of the interactions between calcium ferrite and coal char for chemical looping gasification applications: Identifying reduction routes and modes of oxygen transfer

Chemical Looping Gasification (CLG) is an emerging technology that shows promise for efficient coal gasification by eliminating the need for energy intensive gas separations to achieve a non-nitrogen diluted syngas stream. Oxygen from oxygen carriers, such as CaFe 2 O 4 , are used for coal gasification in place of conventionally produced gaseous oxygen from cryogenic separation of air. These oxygen carriers are unique for their ability to selectively oxidize coal to form syngas and show limited reactivity with syngas components (H 2 , CO). To gain a deeper understanding of how these unique oxygen carriers perform and to offer a first attempt at the reaction modeling of solid mediated interactions of this nature, this study was carried out to determine the kinetic parameters associated with the selective oxidation of coal derived char (Wyodak and Illinois #6) with a metal ferrite, CaFe 2 O 4 . Using thermogravimetric analysis (TGA) coupled with mass spectrometry, the selective oxygen release of metal ferrite in the presence of char by proximal contact was examined. The application of combinatory model fitting approaches was used to describe controlling resistances during oxygen release. A combination of the modified shrinking core model (SCM) with planar oxygen ion diffusion control and reaction order based models was used for kinetic parameter determination. CaFe 2 O 4 particle size plays a major role in the prevailing mode of oxygen release. Particle sizes on the order of 40–50 μm tend to favor first order kinetically controlled regimes independent of geometric and diffusion controls. The probability for oxygen ion diffusion controlling regimes increased when the particle size range of the oxygen carrier was increased up to 350 μm. Char type also impacted the prevalence of the controlling regime. Higher ranked chars react in a slower manner, limiting the gradient for oxygen ion release from the oxygen carrier. Activation energies determined for this process range from 120–200kJ/mol and oxygen ion diffusion coefficients are on the order of 10-8 cm 2 /s. It is suggested that oxygen ion movement is regulated by lattice diffusion out of partially reduced phases (Ca 2 Fe 2 O 5 ) and through reduced outer layers composed of CaO and Fe. The controlled movement of oxygen ions influences the rate of carbon oxidation in the char and therefore the selectivity towards partial oxidation products, which are desirable in CLG applications.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

Biomass pyrolysis devolatilization kinetics of herbaceous and woody feedstocks

Devolatilization kinetics were determined using a modified micropyrolyzer reactor for several biomass feedstocks: switchgrass, corn stover, red oak, and pine. Here, the micropyrolyzer was directly coupled to a flame ionization detector (FID) to track the release of volatiles from the biomass. Time series data from these experiments was analyzed to determine apparent devolatilization rates. Care was taken to assure the experiments were isothermal and kinetically limited calculating a Biot number less than 0.1 and pyrolysis numbers greater than 10, which simplifies the derivation of devolatilization rates. A single, first order reaction was able to model devolatilization rates at temperatures up to 500 °C. No correlation was found between the inorganic content of the biomass and its rate of devolatilization. Apparent activation energies were in the range of 54.9–88.4 kJ mol –1 . The rate coefficient at 500 °C was calculated as 1.90–5.14 s –1 for the four feedstocks.

09 BIOMASS FUELS↗
DOE OSTI2019

Interaction of magnesia-carbon refractory with metallic iron under flash ironmaking conditions

The interaction of a magnesia-carbon refractory with iron under flash ironmaking conditions has been investigated in this work. Oxidation of carbon from the magnesia-carbon refractory took place and the formation of magnesiowustite (Mg x Fe 1-x O) solid solution occurred as a result of the interaction between magnesia (MgO) in the refractory with iron (Fe). A kinetics model for the growth of magnesiowustite (Mg x Fe 1-x O) was developed based on the counterdiffusion of Fe 2+ and Mg 2+ cations through it. Experiments were conducted with iron powder and magnesia-carbon refractory in the temperature range 1200–1400 °C under gas atmospheres relevant to flash ironmaking and analyses of reacted samples using SEM-EDX and EPMA techniques confirmed the formation of magnesiowustite (Mg x Fe 1-x O). Using the kinetics model and the composition profiles determined with EPMA, the values of interdiffusion coefficient ( D ¯ F e - M g ), averaged over the composition range, were calculated. The activation energy ( E a ) for the solid-state diffusion process was determined to be 377 kJ/mol.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Substantial oxygen loss and chemical expansion in lithium-rich layered oxides at moderate delithiation

Delithiation of layered oxide electrodes triggers irreversible oxygen loss, one of the primary degradation modes in lithium-ion batteries. However, the delithiation-dependent mechanisms of oxygen loss remain poorly understood. Here we investigate the oxygen non-stoichiometry in Li 1.18–x Ni 0.21 Mn 0.53 Co 0.08 O 2–δ electrodes as a function of Li content by using cycling protocols with long open-circuit voltage steps at varying states of charge. Surprisingly, we observe substantial oxygen loss even at moderate delithiation, corresponding to 2.5, 4.0 and 7.6 ml O 2 per gram of Li 1.18–x Ni 0.21 Mn 0.53 Co 0.08 O 2–δ after resting at upper capacity cut-offs of 135, 200 and 265 mAh g −1 for 100 h. Our observations suggest an intrinsic oxygen instability consistent with predictions of high oxygen activity at intermediate potentials versus Li/Li + . In addition, we observe a large chemical expansion coefficient with respect to oxygen non-stoichiometry, which is about three times greater than those of classical oxygen-deficient materials such as fluorite and perovskite oxides. Furthermore, our work challenges the conventional wisdom that deep delithiation is a necessary condition for oxygen loss in layered oxide electrodes and highlights the importance of calendar ageing for investigating oxygen stability.

Atomistic models↗
DOE OSTI2017

In situ Studies of Phase Evolution in (Pr 1-x Nd x ) 2 NiO 4 Electrodes with Various Interlayer Chemistries

The interest in Pr2NiO4 (PNO) electrode stems from the necessity to develop active and stable oxygen electrodes (1-6) for solid oxide fuel cells (SOFCs) (7-9). PNO is known for its highly active nature (7,8,10), originating from its superior oxygen ion diffusion, surface exchange coefficient (2,7,9-11) and structural flexibility over a wide temperature region (from 500 to 900oC) (3,12). PNO electrode, however, does undergo structural evolution to form a higher order phase (Pr3Ni2O7) and Pr6O11 (PrOx) (8). The structural change has been a major concern because it possibly links with the performance degradation over long-term operation (7,8) Conventional x-ray diffraction (XRD) has been extensively used to investigate the structural evolution in nickelates in the form of powders or planar electrodes (8,10). This method has two major limitations due to its low flux and low resolution: (1) it might overlook the presence of additional phases in the system, which is especially true for praseodymium nickelates where XRD diffraction patterns of higher order phase(s) (e.g. Pr3Ni2O7) may overlap with the parent PNO phase, making quantification challenging (8); and (2) the quantification of phase evolution in electrochemically operated PNO electrode may show major structural change with almost 100% of the parent phase transition from the conventional XRD analysis, while the transmission electron microscopy (TEM) studies clearly show the regions of preserved PNO phase (7).

Dogdibegovic, Emir↗
DOE OSTI2021

Application of Machine Learning Techniques to an Agent-Based Model of Pantoea

Agent-based modeling (ABM) is a powerful simulation technique which describes a complex dynamic system based on its interacting constituent entities. While the flexibility of ABM enables broad application, the complexity of real-world models demands intensive computing resources and computational time; however, a metamodel may be constructed to gain insight at less computational expense. Here, we developed a model in NetLogo to describe the growth of a microbial population consisting of Pantoea . We applied 13 parameters that defined the model and actively changed seven of the parameters to modulate the evolution of the population curve in response to these changes. We efficiently performed more than 3,000 simulations using a Python wrapper, NL4Py . Upon evaluation of the correlation between the active parameters and outputs by random forest regression, we found that the parameters which define the depth of medium and glucose concentration affect the population curves significantly. Subsequently, we constructed a metamodel, a dense neural network, to predict the simulation outputs from the active parameters and found that it achieves high prediction accuracy, reaching an R 2 coefficient of determination value up to 0.92. Our approach of using a combination of ABM with random forest regression and neural network reduces the number of required ABM simulations. The simplified and refined metamodels may provide insights into the complex dynamic system before their transition to more sophisticated models that run on high-performance computing systems. The ultimate goal is to build a bridge between simulation and experiment, allowing model validation by comparing the simulated data to experimental data in microbiology.

59 BASIC BIOLOGICAL SCIENCES↗
NASA NTRS1972

Reliability of hybrid microcircuit discrete components

Data accumulated during 4 years of research and evaluation of ceramic chip capacitors, ceramic carrier mounted active devices, beam-lead transistors, and chip resistors are presented. Life and temperature coefficient test data, and optical and scanning electron microscope photographs of device failures are presented and the failure modes are described. Particular interest is given to discrete component qualification, power burn-in, and procedures for testing and screening discrete components. Burn-in requirements and test data will be given in support of 100 percent burn-in policy on all NASA flight programs.

Allen, R. V.↗
NASA NTRS1986

Friction-Testing Machine

Testing machine evaluates wear and ignition characteristics of materials in rubbing contact. Offers advantages over other laboratory methods of measuring wear because it simulates operating conditions under which material will actually be used. Machine used to determine wear characteristics, rank and select materials for service with such active oxidizers as oxygen, halogens, and oxides of nitrogen, measure wear characteristics, and determine coefficients of friction.

Benz, F. J.↗
NASA NTRS1987

Lyapunov exponents for infinite dimensional dynamical systems

Classically it was held that solutions to deterministic partial differential equations (i.e., ones with smooth coefficients and boundary data) could become random only through one mechanism, namely by the activation of more and more of the infinite number of degrees of freedom that are available to such a system. It is only recently that researchers have come to suspect that many infinite dimensional nonlinear systems may in fact possess finite dimensional chaotic attractors. Lyapunov exponents provide a tool for probing the nature of these attractors. This paper examines how these exponents might be measured for infinite dimensional systems.

Mhuiris, Nessan Mac Giolla↗
NASA NTRS1988

Efficient spacecraft formationkeeping with consideration of ballistic coefficient control

The extent to which drag can be used to enhance retrieval and servicing of platforms in the Space Staion environment is investigated for the case when separations on the order of several hundred or even thousands of kilometers occur over extended, but predefined, periods of time. The nature of the problem is formulated, the analytical tools used are described, and the mathematical foundation of the analysis is presented. Results are reported for the cases of formation flying cycles without ballistic coefficient control, formation flying with controlled relative decay, and the effects of varying solar activity.

Mathews, Michael↗
NASA NTRS1999

Three-dimensional segmentation of luminal and adventitial borders in serial intravascular ultrasound images

Intravascular ultrasound (IVUS) provides exact anatomy of arteries, allowing accurate quantitative analysis. Automated segmentation of IVUS images is a prerequisite for routine quantitative analyses. We present a new three-dimensional (3D) segmentation technique, called active surface segmentation, which detects luminal and adventitial borders in IVUS pullback examinations of coronary arteries. The technique was validated against expert tracings by computing correlation coefficients (range 0.83-0.97) and William's index values (range 0.37-0.66). The technique was statistically accurate, robust to image artifacts, and capable of segmenting a large number of images rapidly. Active surface segmentation enabled geometrically accurate 3D reconstruction and visualization of coronary arteries and volumetric measurements.

NASA Discipline Cardiopulmonary↗
NASA NTRS2015

The Suomi National Polar-Orbiting Partnership (SNPP): Continuing NASA Research and Applications

The Suomi National Polar-orbiting Partnership (SNPP) satellite was successfully launched into a polar orbit on October 28, 2011 carrying 5 remote sensing instruments designed to provide data to improve weather forecasts and to increase understanding of long-term climate change. SNPP provides operational continuity of satellite-based observations for NOAA's Polar-orbiting Operational Environmental Satellites (POES) and continues the long-term record of climate quality observations established by NASA's Earth Observing System (EOS) satellites. In the 2003 to 2011 pre-launch timeframe, NASA's SNPP Science Team assessed the adequacy of the operational Raw Data Records (RDRs), Sensor Data Records (SDRs), and Environmental Data Records (EDRs) from the SNPP instruments for use in NASA Earth Science research, examined the operational algorithms used to produce those data records, and proposed a path forward for the production of climate quality products from SNPP. In order to perform these tasks, a distributed data system, the NASA Science Data Segment (SDS), ingested RDRs, SDRs, and EDRs from the NOAA Archive and Distribution and Interface Data Processing Segments, ADS and IDPS, respectively. The SDS also obtained operational algorithms for evaluation purposes from the NOAA Government Resource for Algorithm Verification, Independent Testing and Evaluation (GRAVITE). Within the NASA SDS, five Product Evaluation and Test Elements (PEATEs) received, ingested, and stored data and performed NASA's data processing, evaluation, and analysis activities. The distributed nature of this data distribution system was established by physically housing each PEATE within one of five Climate Analysis Research Systems (CARS) located at either at a NASA or a university institution. The CARS were organized around 5 key EDRs directly in support of the following NASA Earth Science focus areas: atmospheric sounding, ocean, land, ozone, and atmospheric composition products. The PEATES provided the system level interface with members of the NASA SNPP Science Team and other science investigators within each CARS. A sixth Earth Radiation Budget CARS was established at NASA Langley Research Center (NASA LaRC) to support instrument performance, data evaluation, and analysis for the SNPP Clouds and the Earth's Radiant Budget Energy System (CERES) instrument. Following the 2011 launch of SNPP, spacecraft commissioning, and instrument activation, the NASA SNPP Science Team evaluated the operational RDRs, SDRs, and EDRs produced by the NOAA ADS and IDPS. A key part in that evaluation was the NASA Science Team's independent processing of operational RDRs and SDRs to EDRs using the latest NASA science algorithms. The NASA science evaluation was completed in the December 2012 to April 2014 timeframe with the release of a series of NASA Science Team Discipline Reports. In summary, these reports indicated that the RDRs produced by the SNPP instruments were of sufficiently high quality to be used to create data products suitable for NASA Earth System science and applications. However, the quality of the SDRs and EDRs were found to vary greatly when considering suitability for NASA science. The need for improvements in operational algorithms, adoption of different algorithmic approaches, greater monitoring of on-orbit instrument calibration, greater attention to data product validation, and data reprocessing were prominent findings in the reports. In response to these findings, NASA, in late 2013, directed the NASA SNPP Science Team to use SNPP instrument data to develop data products of sufficiently high quality to enable the continuation of EOS time series data records and to develop innovative, practical applications of SNPP data. This direction necessitated a transition of the SDS data system from its pre-launch assessment mode to one of full data processing and production. To do this, the PEATES, which served as NASA's data product testing environment during the prelaunch and early on-orbit periods, were transitioned to Science Investigator-led Processing Systems (SIPS). The distributed data architecture was maintained in this new system by locating the SIPS at the same institutions at which the CARS and PEATES were located. The SIPS acquire raw SNPP instrument Level 0 (i.e. RDR) data over the full SNPP mission from the NOAA ADS and IDPS through the NASA SDS Data Distribution and Depository Element (SD3E). The SIPS process those data into NASA Level 1, Level 2, and global, gridded Level 3 standard products using peer-reviewed algorithms provided by members of the NASA Science Team. The SIPS work with the NASA SNPP Science Team in obtaining enhanced, refined, or alternate real-time algorithms to support the capabilities of the Direct Readout Laboratory (DRL). All data products, algorithm source codes, coefficients, and auxiliary data used in product generation are archived in an assigned NASA Distributed Active Archive Center (DAAC).

remote sensing↗
DOE OSTI2019

On the Thermal Activation of Conductivity Electrons in a p-Type HgTe/CdHgTe Double Quantum Well with HgTe Layers of Critical Width

The temperature dependences of the Hall coefficient and magnetoresistivity of a p-type HgTe/CdHgTe double quantum well with HgTe layers of critical thickness in the temperature range T = 35–300 K under magnetic fields up to 9 T are investigated. The position of the earlier observed reentrant quantum Hall transition from plateau i = 1 to plateau i = 2 is found to be close to the transition field from light to heavy holes with an increase in the magnetic field in the classical Hall effect. It is found that thermally activated light electrons contribute to the Hall effect along with light and heavy holes at T ≥ 35 K. The activation energy of electrons is estimated from the temperature dependence of the electron concentration as 28 meV, which exceeds the calculated value from the lateral maximum of the valence subband to the edge of the lowest conduction subband, probably because of heterostructure asymmetry.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Structural, Electronic, Magnetic and Optical Investigations of Half-Heusler Compounds YZSb (Z = Cr, Mn): FP-LAPW Method

Half-Heusler compounds YZSb (Z = Cr, Mn) are theoretically explored in the framework of density functional theory (DFT). We have investigated a number of different properties with the help of the WIEN2k simulation package. Equilibrium lattice constants fall in the range 6.0–7.0 Å for both compounds. Elastic properties are also studied and it is found that the compound YCrSb is of brittle and YMnSb is of ductile nature as indicated by a number of parameters including Cauchy pressure, Pugh’s ratio and Poisson’s ratio. Electronically, these compounds are found to be half-metals as their spin-up states are semiconducting and hence 100% spin polarized at the Fermi level while spin-down states are conducting. The total magnetic moments are equal to 4μ{sub B} and 3.15μ{sub B} for YCrSb and YMnSb, respectively. The optical properties including dielectric function, reflectivity, refractive index, conductivity and absorption coefficients are calculated and discussed. Optical characteristics of the compounds hint that they are more active in the infrared region.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2020

Oxidation kinetics of biochar from woody and herbaceous biomass

The goal of this study was to determine oxidation kinetics for biochar produced from fast pyrolysis of various biomass feedstocks. In particular, the role of inherent ash content on the oxidation rate was evaluated. Thermogravimetric analysis (TGA) and fluidized bed combustion experiments were used to explore oxidation kinetics of six fast pyrolysis produced biochars with diverse ash content. Here, the reaction rates varied by a factor of three under chemical kinetic-limited conditions, demonstrating inorganic content impacts oxidation rate. Chemical kinetic rate coefficients were proposed as a function of compositional parameters to determine overall fit and impact. Potassium content was found to have a positive correlation, best describing the differences in the oxidation kinetic rate coefficients. Additionally, feedstocks were subjected to a 1 M HCl acid wash mitigating the catalytic activity of the metals. Acid washed biochars had lower oxidation kinetic rates compared to their unwashed counterparts, indicating the removal of catalytically active metals reduced oxidation rate. Gas composition (CO/CO 2 ) was measured during fluidized bed experiments for both acid-washed and unwashed biochars, which varied between the six biochars. Formation of CO 2 was greatly affected by catalytic metals, finding potassium content to correlate well with a higher percentage of CO 2 formation as compared to CO. Comparison of oxidation rates were made between the two experimental apparatuses to measure the effect of attrition on biochar oxidation.

09 BIOMASS FUELS↗
DOE OSTI2017

On the indiscriminate use of imported emission factors in environmental impact assessment: A case study in Chile

Environmental Impact Assessment (EIA) aims to determine if the environmental effect of an activity or project complies with standards and regulations. A primary component of the environment to evaluate is air and the effect that various activities can have on its quality. To this end, emission factors (EFs), which are empirical coefficients or mathematical relationships, are normally used. The present research critically analyzes the implications and consequences of using imported EFs in environmental impact studies (EISs), taking as case of study the situation in Chile. Among the main results, the widespread use of EFs in EISs in the country and the lack of assessments of their actual applicability stand out. In addition, the official guidelines related to emissions estimation that are used for EIA in the country mostly include EFs derived elsewhere, without considering the recommendations or restrictions that the original sources indicate for their use. Finally, the broad use of default values defined for the Metropolitan Region in Central Chile, is highly questionable for a country that extends north-south along more than 35° of latitude, with wide variability in climate, traffic conditions, population, soil types, etc. Finally, it is very likely that situations similar to those observed in the present work occurs in other countries with young environmental impact assessment systems, and therefore, that the results herein presented should be of general interest and relevance. - Highlights: • Emission factors are widely used in environmental impact assessment in Chile. • There is a lack of a proper understanding of the limitations of EFs for EIA. • Imported emission factors use requires caution and full understanding. • Misuse of foreign EFs may have serious environmental and economic consequences.

54 ENVIRONMENTAL SCIENCES↗