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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 145 records · Page 8
All sourcesNASA NTRSDOE OSTI
DOE OSTI2012

Pore size effects on the sorption of supercritical carbon dioxide in mesoporous CPG-10 silica

Excess sorption isotherms of supercritical carbon dioxide in mesoporous CPG-10 silica glasses with nominal pore sizes of 75 (7.5 nm) and 350 (35 nm) were measured gravimetrically at 35 C and 50 C and pressures of 0-200 bar. Formation of broad maxima in the excess sorption was observed at fluid densities below the bulk critical density. Positive values of excess sorption were measured at bulk densities below about 0.65-0.7 g/cm3, whereas zero and negative values were obtained at higher densities, indicating that the interfacial fluid becomes less dense than the corresponding bulk fluid at high fluid densities. A shift of the excess sorption peak position to higher fluid density is found with increasing pore width. The excess sorption of CO2 normalized to the specific surface area is higher for the 35 nm pore size material, suggesting pore confinement effects. Conversely, the pore volume normalized excess sorption is higher for the 7.5 nm pore size material. Assessment of mean pore density reveals regions of constant pore fluid density, located between the excess sorption peak and the adsorption/depletion transition. Both materials exhibit such regions of constant mean pore fluid density as a function of bulk CO2 density at the lower temperature of 35 C, but not at 50 C. The results of this study suggest that the CO2 storage capacity in quartz-rich reservoirs is higher for sites with low temperature and rock textures characterized by narrow pores with high surface to volume ratios.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2016

Influence of particle size, cycling rate and temperature on the lithiation process of anatase TiO 2

The nature of a phase transition plays an important role in controlling the kinetics of reaction of an electrode material in a lithium-ion battery. The actual phase transition path can be affected by particle size and cycling rate. In this study, we investigated the phase transition process during the electrochemical Li intercalation of anatase TiO 2 as a function of particle size (25 nm and 100 nm), cycling rate (1C, 2C, 5C, 10C, 20C) and temperature (room temperature and 80 °C) by in situ synchrotron X-ray diffraction. The phase transition was found to be affected by the particle size: the 100 nm particles react simultaneously via a conventional nucleation and growth, i.e. two-phase, mechanism, while the 25 nm particles react sequentially via a two-phase mechanism. The Li miscibility gap decreases with increasing cycling rate, yet the phase separation was not suppressed even at a cycle rate of 20C. An increase in temperature from room temperature to 80 °C significantly improves the electrode's electrochemical performance despite undergoing a two-phase reaction. The failure to observe a continuous structural transition from tetragonal TiO 2 to orthorhombic Li 0.5 TiO 2 even at high rates and elevated temperature was attributed to the high energy barrier of a continuous phase transition path.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2014

Determination of lateral size distribution of type-II ZnTe/ZnSe stacked submonolayer quantum dots via spectral analysis of optical signature of the Aharanov-Bohm excitons

For submonolayer quantum dot (QD) based photonic devices, size and density of QDs are critical parameters, the probing of which requires indirect methods. We report the determination of lateral size distribution of type-II ZnTe/ZnSe stacked submonolayer QDs, based on spectral analysis of the optical signature of Aharanov-Bohm (AB) excitons, complemented by photoluminescence studies, secondary-ion mass spectroscopy, and numerical calculations. Numerical calculations are employed to determine the AB transition magnetic field as a function of the type-II QD radius. The study of four samples grown with different tellurium fluxes shows that the lateral size of QDs increases by just 50%, even though tellurium concentration increases 25-fold. Detailed spectral analysis of the emission of the AB exciton shows that the QD radii take on only certain values due to vertical correlation and the stacked nature of the QDs.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2016

Optimal Sizing and Placement of Battery Energy Storage in Distribution System Based on Solar Size for Voltage Regulation

This paper proposes a new strategy to achieve voltage regulation in distributed power systems in the presence of solar energy sources and battery storage systems. The goal is to find the minimum size of battery storage and its corresponding location in the network based on the size and place of the integrated solar generation. The proposed method formulates the problem by employing the network impedance matrix to obtain an analytical solution instead of using a recursive algorithm such as power flow. The required modifications for modeling the slack and PV buses (generator buses) are utilized to increase the accuracy of the approach. The use of reactive power control to regulate the voltage regulation is not always an optimal solution as in distribution systems R/X is large. In this paper the minimum size and the best place of battery storage is achieved by optimizing the amount of both active and reactive power exchanged by battery storage and its gridtie inverter (GTI) based on the network topology and R/X ratios in the distribution system. Simulation results for the IEEE 14-bus system verify the effectiveness of the proposed approach.

14 SOLAR ENERGY↗
DOE OSTI2012

Examination of a Size-Change Test for Photovoltaic Encapsulation Materials: Preprint

We examine a proposed test standard that can be used to evaluate the maximum representative change in linear dimensions of sheet encapsulation products for photovoltaic modules (resulting from their thermal processing). The proposed protocol is part of a series of material-level tests being developed within Working Group 2 of the Technical Committee 82 of the International ElectrotechnicalCommission. The characterization tests are being developed to aid module design (by identifying the essential characteristics that should be communicated on a datasheet), quality control (via internal material acceptance and process control), and failure analysis. Discovery and interlaboratory experiments were used to select particular parameters for the size-change test. The choice of a sandsubstrate and aluminum carrier is explored relative to other options. The temperature uniformity of +/- 5C for the substrate was confirmed using thermography. Considerations related to the heating device (hot-plate or oven) are explored. The time duration of 5 minutes was identified from the time-series photographic characterization of material specimens (EVA, ionomer, PVB, TPO, and TPU). Thetest procedure was revised to account for observed effects of size and edges. The interlaboratory study identified typical size-change characteristics, and also verified the absolute reproducibility of +/- 5% between laboratories.

14 SOLAR ENERGY↗
DOE OSTI2015

Synthesis of Copper Birnessite, Cu x MnO y ·nH 2 O with Crystallite Size Control: Impact of Crystallite Size on Electrochemistry

This report describes the first detailed electrochemical examination of a series of copper birnessite samples under lithium-based battery conditions, allowing a structure/function analysis of the electrochemistry and related material properties. To obtain the series of copper birnessite samples, a novel synthetic approach for the preparation of copper birnessite, Cu x MnO y ·nH 2 O is reported. The copper content (x) in Cu x MnO y ·nH 2 O, 0.28 >= x >= 0.20, was inversely proportional to crystallite size, which ranged from 12 to 19 nm. The electrochemistry under lithium-based battery conditions showed that the higher copper content (x = 0.28) and small crystallite size (similar to 12 nm) sample delivered similar to 194 mAh/g, about 20% higher capacity than the low copper content (x = 0.22) and larger crystallite size (similar to 19 nm) material. In addition, Cu x MnO y ·nH 2 O displays quasi-reversible electrochemistry in magnesium based electrolytes, indicating that copper birnessite could be a candidate for future application in magnesium-ion batteries.

25 ENERGY STORAGE↗
DOE OSTI2016

Usage of Parameterized Fatigue Spectra and Physics-Based Systems Engineering Models for Wind Turbine Component Sizing: Preprint

Software models that use design-level input variables and physics-based engineering analysis for estimating the mass and geometrical properties of components in large-scale machinery can be very useful for analyzing design trade-offs in complex systems. This study uses DriveSE, an OpenMDAO-based drivetrain model that uses stress and deflection criteria to size drivetrain components within a geared, upwind wind turbine. Because a full lifetime fatigue load spectrum can only be defined using computationally-expensive simulations in programs such as FAST, a parameterized fatigue loads spectrum that depends on wind conditions, rotor diameter, and turbine design life has been implemented. The parameterized fatigue spectrum is only used in this paper to demonstrate the proposed fatigue analysis approach. This paper details a three-part investigation of the parameterized approach and a comparison of the DriveSE model with and without fatigue analysis on the main shaft system. It compares loads from three turbines of varying size and determines if and when fatigue governs drivetrain sizing compared to extreme load-driven design. It also investigates the model's sensitivity to shaft material parameters. The intent of this paper is to demonstrate how fatigue considerations in addition to extreme loads can be brought into a system engineering optimization.

17 WIND ENERGY↗
NASA NTRS1979

Spatial quantification of maps or images - Cell size or pixel size implications

The paper discusses spatial quantification of maps or images. Spatial accuracies evaluated by mapping and inventory measures were observed with a range of cell sizes for a 10.36 sq km soil survey segment. The distribution of interboundary distances in a map was evaluated as unique, characterizing information; experimentally observed relationships between accuracy and cell size and interboundary distance distribution parameters and cell size led to a model of the process of spatial quantization. Grid positioning effects were evaluated and were significant only at the level of individual mapping units; two generations of 'universal' process models were derived, implemented, and evaluated.

Wehde, M. E.↗
NASA NTRS1993

Light scattering by size-shape distributions of randomly oriented axially symmetric particles of a size comparable to a wavelength

Rigorously light scattering by size-shape distributions of randomly oriented axially symmetric particles are calculated by the T-matrix method, as extended to randomly oriented scatterers. The computational scheme is described along with a newly developed convergence procedure that makes it possible to substantially reduce computer time and storage requirements. The elements of the Stokes scattering matrix for a power-law size distribution of randomly oriented moderately aspherical spheroids are shown to be much smoother than and differ substantially from those of equivalent monodisperse spheroids; averaging over orientations does not eliminate the necessity of averaging over particle sizes. The angular-scattering behavior of the ensembles of nonspherical particles is found to be significantly different from that of the equivalent polydisperse spheres.

Mishchenko, Michael I.↗
DOE OSTI2017

Synthesis and characterization of metastable, 20 nm-sized Pna2{sub 1}-LiCoPO{sub 4} nanospheres

The majority of research activities on LiCoPO{sub 4} are focused on the phospho-olivine (space group Pnma), which is a promising high-voltage cathode material for Li-ion batteries. In contrast, comparably little is known about its metastable Pna2{sub 1} modification. Herein, we present a comprehensive study on the structure–property relationships of 15–20 nm Pna2{sub 1}-LiCoPO{sub 4} nanospheres prepared by a simple microwave-assisted solvothermal process. Unlike previous reports, the results indicate that the compound is non-stoichiometric and shows cation-mixing with Co ions on the Li sites, which provides an explanation for the poor electrochemical performance. Co L{sub 2,3}-edge X-ray absorption spectroscopic data confirm the local tetrahedral symmetry of Co{sup 2+}. Comprehensive studies on the thermal stability using thermogravimetric analysis, differential scanning calorimetry, and in situ powder X-ray diffraction show an exothermic phase transition to olivine Pnma-LiCoPO{sub 4} at 527 °C. The influence of the atmosphere and the particle size on the thermal stability is also investigated. - Graphical abstract: Blue nano-sized Pna2{sub 1}-LiCoPO{sub 4,} featuring tetrahedrally-coordinated Co{sup 2+}, was synthesized in a rapid one-step microwave-assisted solvothermal process. The phase relation between this metastable and the stable polymorph was analyzed and electrochemical properties are discussed. - Highlights: • Preparation of uniform 15–20 nm nanospheres of metastable Pna2{sub 1}-LiCoPO{sub 4} polymorph. • Structure redetermination shows cation-mixing (Co blocking Li sites). • In situ investigation of phase transformation to olivine Pnma-LiCoPO{sub 4} at 527 °C. • Pna2{sub 1}-LiCoPO{sub 4} reemerges as a stable high-temperature phase above 800 °C. • X-ray absorption spectroscopy confirms local tetrahedral symmetry (T{sub d} Co{sup 2+}).

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗