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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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All sourcesNASA NTRSDOE OSTI
DOE OSTI2022

Process Modeling of CO 2 Absorption with Monoethanolamine Aqueous Solutions Using Rotating Packed Beds

A first-principle process simulation model is presented for the chemical absorption of carbon dioxide (CO 2 ) with monoethanolamine (MEA) aqueous solutions using rotating packed beds (RPB). Built on a proven rate-based packed bed absorber model, the RPB model rigorously simulates the phase and chemical equilibria at the vapor-liquid interface, the heat and mass transfer across the gas and liquid films, the fast reactions between MEA and CO 2 in the liquid film, and the RPB hydraulics. Here, estimation of the mass transfer rate across the liquid film is central to accurate simulation of the CO 2 absorption process with MEA aqueous solutions. We show that the literature lab-scale RPB data for CO 2 removal efficiency can be satisfactorily correlated by introducing a correction factor for the effective packing surface area predicted by the Onda correlation. Given the validated RPB model, we further show that, among the gas-phase mass transfer coefficient, the liquid-phase mass transfer coefficient, and the reaction rate constant for the reaction between amine and CO 2 , the reaction rate constant is the controlling step with the highest potential to enhance the CO 2 absorption performance in RPB.

42 ENGINEERING↗
DOE OSTI2018

Systematic DFT study of the impact of anionic variations on the physical properties of Cd1-xMnxX (XS, Se, Te; x = 6.25%)

Highlights: • The structural and electronic properties are investigated with most accurate mBJ potential. • The FM state stability is illustrated for Cd{sub 0.9375}Mn{sub 0.0625}S/Se/Te DMSs. • The FM semiconducting nature depicts potential applications in magneto-optic applications. • The absorption shifts within the visible range with S to Te variation that is verified by E{sub g}. • Thermoelectric properties indicate dominant hole-carriers and suitability at high temperatures. - Abstract: The structural and electronic properties are theoretically investigated for Cd{sub 1-x}Mn{sub x}X (XS, Se, Te; x = 6.25%) diluted magnetic semiconductors, which are further employed for extracting the magnetic, optical and thermoelectric properties using modified-Becke-Johnson (mBJ) potential. Ferromagnetic state stability is confirmed through the computed enthalpy of formation and the cohesive energies. The electronic properties elucidate Cd{sub 1-x}Mn{sub x}X (XS, Se, Te; x = 6.25%) as ferromagnetic semiconductors because both spin channels have Fermi energy level (E{sub F}) within the band gap, depicting potential applications in spintronic devices. The calculated optical response indicates shifts in the absorption within the visible energy that is consistent with the computed direct band gap values (1.9 eV–3.1 eV). Thermoelectric properties observed within 200 K–800 K show positive Seebeck coefficient indicating holes as majority charge carriers. Although Mn-doping suppresses the power factor, however, it improves with temperature, showing a potential for optimizing the thermoelectric performance.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2011

Development of a prototype gantry system for preclinical x-ray phase-contrast computed tomography

Purpose: To explore the potential of grating-based x-ray phase-contrast imaging for clinical applications, a first compact gantry system was developed. It is designed such that it can be implemented into an in-vivo small-animal phase-contrast computed tomography (PC-CT) scanner. The purpose of the present study is to assess the accuracy and quantitativeness of the described gantry in both absorption and phase-contrast. Methods: A phantom, containing six chemically well-defined liquids, was constructed. A tomography scan with cone-beam reconstruction of this phantom was performed yielding the spatial distribution of the linear attenuation coefficient {mu} and decrement {delta} of the complex refractive index. Theoretical values of {mu} and {delta} were calculated for each liquid from tabulated data and compared with the experimentally measured values. Additionally, a color-fused image representation is proposed to display the complementary absorption and phase-contrast information in a single image. Results: Experimental and calculated data of the phantom agree well confirming the quantitativeness and accuracy of the reconstructed spatial distributions of {mu} and {delta}. The proposed color-fused image representation, which combines the complementary absorption and phase information, considerably helps in distinguishing the individual substances. Conclusions: The concept of grating-based phase-contrast computed tomography (CT) can be implemented into a compact, cone-beam geometry gantry setup. The authors believe that this work represents an important milestone in translating phase-contrast x-ray imaging from previous proof-of-principle experiments to first preclinical biomedical imaging applications on small-animal models.

62 RADIOLOGY AND NUCLEAR MEDICINE↗
DOE OSTI2014

Optical nonlinear dynamics in ZnS from femtosecond laser pulses

A wavelength swapping nondegenerate pump-probe technique to measure the magnitudes of the nonlinear optical dynamics as well as the relaxation time of electrons in high energy levels is presented using a ZnS single crystal wafer as an example. By pumping the sample with 800 nm femtosecond pulses and probing at 400 nm, nondegenerate two-photon absorption (N-2PA) happens exclusively, and the measured curves only show instantaneous features without relaxation tails. The N-2PA coefficient was derived explicitly as 7.52 cm/GW. Additionally, when the wavelengths of the pump and probe beams are swapped, extra information about the relaxation time of the hot electrons excited in the conduction band is obtained. The combined results above are helpful for evaluating the characteristics of an optical switches based on ZnS or other materials with respect to its nonlinear optical dynamic aspect.

36 MATERIALS SCIENCE↗
NASA NTRS1972

Extreme-ultraviolet emission from solar prominences.

Spectra and spectroheliograms of prominences have been obtained at wavelengths of 300 to 1400 A from instruments aboard the OSO 4 and OSO 6 spacecraft. Quiescent prominences appear in emission above the limb for all strong lines formed at temperatures below 300,000 K, but not at higher temperatures. The gas pressure in the 100,000-K transition zone around prominences is approximately equal to that in the cooler (6500 K) central regions. The temperature and the hydrogen ground-state departure coefficient in the central regions are determined from the Lyman-continuum spectrum. Prominences on the disk (filaments) are visible in absorption in many lines, especially those at wavelengths below the hydrogen Lyman limit at 912 A.

Noyes, R. W.↗
NASA NTRS1993

Photodissociation in the atmosphere of Mars - Impact of high resolution, temperature-dependent CO2 cross-section measurements

We have investigated the impact of high resolution, temperature-dependent CO2 cross-section measurements, reported by Lewis and Carver (1983), on calculations of photodissociation rate coefficients in the Martian atmosphere. We find that the adoption of 50 A intervals for the purpose of computational efficiency results in errors in the calculated values for photodissociation of CO2, H2O, and O2 which are generally not above 10 percent, but as large as 20 percent in some instances. These are acceptably small errors, especially considering the uncertainties introduced by the large temperature dependence of the CO2 cross section. The inclusion of temperature-dependent CO2 cross sections is shown to lead to a decrease in the diurnally averaged rate of CO2 photodissociation as large as 33 percent at some altitudes, and increases of as much as 950 percent and 80 percent in the photodissociation rate coefficients of H2O and O2, respectively. The actual magnitude of the changes depends on the assumptions used to model the CO2 absorption spectrum at temperatures lower than the available measurements, and at wavelengths longward of 1970 A.

Anbar, A. D.↗
NASA NTRS2005

Sulfur Oxidation and Contrail Precursor Chemistry

Sulfuric acid (H2SO4), formed in commercial aircraft operations via Fuel-S (right arrow) SO2 + SO3 (right arrow) H2SO4, plays an important role in affecting the global climate change through atmospheric chemical reactions and radiative forcing. Measurement of the sulfur oxidation rates is critical to the understanding of the contrail formation. The principle reaction pathway is SO2 + O + M (right arrow) SO3 + M. Although there are many measurements for the rates of this reaction, it has never been measured in the temperature and pressure regime available to aircraft operation. In this investigation, a series of experiments were performed behind the reflected shock waves in a shock tube. OH radicals were produced in lean, shock heated SO2/H2/O2/Ar mixtures. The reaction progress was followed using OH absorption spectroscopy at 310 nm. The data were analyzed with the aid of computer modeling/simulation. The mean value of the rate coefficients of R21 determined is k(sub 21,0)/[M]= 3.9 x 10(exp 15) cm(sup 6) per square mole per second at T = 960 - 1150 K and rho = 16-30 micromole per cubic centimeter with uncertainty limits of plus or minus 30%. A non-Arrhenius fit to our data together with all existing data gives k(sub 21,0)/[M] = 1.3 x 10(exp 24) T (exp -2.5) exp(-2350 K/T) cm(sup 6) per square mole per second at T = 300 - 2500 K with the same uncertainty limits given above. The calculated conversion of S(IV)(SO2) to S(VI) (SO3 + H2SO4) was about 2% in our experimental conditions.

DeWitt, Kenneth↗
DOE OSTI2011

Temperature dependent optical properties of pentacene films on zinc oxide

The optical transitions of pentacene films deposited on ZnO have been studied by absorption spectroscopy as a function of temperature in the range of room temperature down to 10 K. The pentacene films were prepared with thicknesses of 10 nm, 20 nm, and 100 nm on the ZnO-O(000-1) surface by molecular beam deposition. A unique temperature dependence has been observed for the two Davydov components of the excitons for different film thicknesses. At room temperature, the energetic positions of the respective absorption bands are the same for all films, whereas the positions differ more than 20 meV at 10 K caused by the very different expansion coefficients of pentacene and ZnO. Although the pentacene is just bonded via van der Waals interaction to the ZnO substrate, the very first pentacene monolayer (adlayer) is forced to keep the initial position on the ZnO surface and suffering, therefore, a substantial tensile strain. For all the subsequent pentacene monolayers, the strain is reduced step by step resulting electronically in a strong potential gradient at the interface.

36 MATERIALS SCIENCE↗
NASA NTRS1998

Air- and N2-Broadening Coefficients and Pressure-Shift Coefficients in the C-12(O2-16) Laser Bands

In this paper we report the pressure broadening and the pressure-induced line shift coefficients for 46 individual rovibrational lines in both the (12)C(16)O2, 00(sup 0)1-(10(sup 0)0-02(sup 0)0)I, and 00(sup 0)1-(10(sup 0)0-02(sup 0)0)II, laser bands (laser band I centered at 960.959/cm and laser band II centered at 1063.735/cm) determined from spectra recorded with the McMath-Pierce Fourier transform spectrometer. The results were obtained from analysis of 10 long-path laboratory absorption spectra recorded at room temperature using a multispectrum nonlinear least-squares technique. Pressure effects caused by both air and nitrogen have been investigated. The air-broadening coefficients determined in this study agree well with the values in the 1996 HITRAN database; ratios and standard deviations of the ratios of the present air-broadening measurements to the 1996 HITRAN values for the two laser bands are: 1.005(15) for laser band I and 1.005(14) for laser band II. Broadening by nitrogen is 3 to 4% larger than that of air. The pressure-induced line shift coefficients are found to be transition dependent and different for the P- and R-branch lines with same J" value. No noticeable differences in the shift coefficients caused by air and nitrogen were found. The results obtained are compared with available values previously reported in the literature.

Devi, V. Malathy↗
NASA NTRS1991

H2/O2 three-body rates at high temperatures

Hydrogen atoms are produced in the presence of excess O2, and the first-order decay are studied as a function of temperature and pressure in order to obtain the rate coefficient for the three-body reaction between H-atoms and O2. Attention is focused on the kinetic scheme employed as well as the reaction cell and photolysis and probe laser system. A two-photon laser-induced fluorescence technique is employed to detect H-atoms without optical-thickness or O2-absorption problems. Results confirm measurements reported previously for the H + O2 + N2 reaction at 300 K and extend these measurements to higher temperatures. Preliminary data indicate non-Arrehenius-type behavior of this reaction rate coefficient as a function of temperature. Measurements of the rate coefficient for H + O2 + Ar reaction at 300 K give a rate coefficient of 2.1 +/- 0.1 x 10 to the -32nd cm exp 6/molecule sec.

Marinelli, William J.↗
DOE OSTI2015

Studies on VO{sub x} thin films deposited over Si{sub 3}N{sub 4} coated Si substrates

Vanadium oxide (VO{sub x}) thin films were deposited on to the silicon nitride (Si{sub 3}N{sub 4}) coated silicon (Si) substrate using reactive direct current magnetron sputtering at different substrate temperatures (T{sub s}). The deposited films were characterized for their structural, morphological, optical and electrical properties. The average grain size of the deposited films was in the range of 95 to 178 nm and the strain varied from 0.071 to 0.054 %. The optical bandgap values of the films were evaluated using UV-Vis spectroscopy and lies in the range of 2.46 to 3.88 eV. The temperature coefficient of resistance (TCR) for the film deposited at 125 °C was -1.23%/°C with the sheet resistivity of 2.7 Ω.cm.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
NASA NTRS1991

The Fundamental Quadrupole Band of (14)N2: Line Positions from High-Resolution Stratospheric Solar Absorption Spectra

The purpose of this note is to report accurate measurements of the positions of O- and S-branch lines of the (1-0) vibration-rotation quadrupole band of molecular nitrogen ((14)N2) and improved Dunham coefficients derived from a simultaneous least-squares analysis of these measurements and selected infrared and far infrared data taken from the literature. The new measurements have been derived from stratospheric solar occultation spectra recorded with Fourier transform spectrometer (FTS) instruments operated at unapodized spectral resolutions of 0.002 and 0.01 /cm. The motivation for the present investigation is the need for improved N2 line parameters for use in IR atmospheric remote sensing investigations. The S branch of the N2 (1-0) quadrupole band is ideal for calibrating the line-of-sight airmasses of atmospheric spectra since the strongest lines are well placed in an atmospheric window, their absorption is relatively insensitive to temperature and is moderately strong (typical line center depths of 10 to 50% in high-resolution ground-based solar spectra and in lower stratospheric solar occultation spectra), and the volume mixing ratio of nitrogen is constant in the atmosphere and well known. However, a recent investigation has'shown the need to improve the accuracies of the N2 fine positions, intensities, air-broadened half-widths, and their temperature dependences to fully exploit this calibration capability (1). The present investigation addresses the problem of improving the accuracy of the N2 line positions.

Rinsland, C. P.↗
DOE OSTI2020

Thermophysical properties of high-density, sintered monoliths of yttrium dihydride in the range 373–773 K

Yttrium dihydride is a promising nuclear reactor moderator for high-temperature, thermal micro-reactors due to its ability to retain hydrogen to high temperatures while having a relatively low impact on neutron economy. However, it is difficult to fabricate yttrium dihydride in high-density, near net-shape monoliths for moderator applications due to challenges associated with the hydrogen absorption process. Here, high-density monoliths of yttrium dihydride were prepared by powder metallurgical methods. The lattice strain and thermal expansion coefficient were measured using neutron diffraction of powders of directly-hydrided yttrium, while the molar heat capacity and thermal diffusivity of sintered yttrium dihydride were measured using differential scanning calorimetry (DSC) and laser flash analysis (LFA), respectively. The molar heat capacity of yttrium dihydride was also calculated using density functional theory (DFT) for comparison. These parameters were used to then calculate the thermal conductivity and resistivity of yttrium dihydride as a function of temperature. The thermophysical properties of materials produced by both methods were observed to be consistent with the values from literature for yttrium dihydride. Due to the novelty of producing yttrium dihydride by powder metallurgical methods, this result indicated that the sintered monoliths were of high quality and that powder metallurgy is a viable method for large-scale production of yttrium dihydride monoliths for nuclear reactor moderator applications.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Tritium adsorption and absorption on (100) and (001) surfaces of pure and tin defective zirconium

Zirconium alloys such as zircaloy-4 are used as tritium (T) getter materials in tritium-producing burnable absorber rods (TPBARs) due to their ability to capture T, thereby forming metal hydrides. Developing an understanding of T adsorption onto zircaloy prior to diffusion into the subsurface is relevant for rational tritium getter and TPBAR design, to improve material properties for nuclear applications. Herein, density functional theory calculations revealed the preferred binding sites for T adsorption on Zr(001) and Zr(100). The energy barriers of T transfer, along the surface and from the surface to the subsurface were computed. The adsorption properties of Zr(001) were found to be superior to those of Zr(100). Surface tin impurities were found to strongly repel T. The presence of subsurface and surface tin resulted in higher absorption energy barriers for both the forward and reverse processes. Based on the calculated energy barriers, a surface to surface T diffusion coefficient of 9.53 × 10 -10 m 2 s -1 is expected for pristine Zr(001). Finally, a surface to subsurface T diffusion coefficient on the order of 10 -13 m 2 s -1 is predicted in pristine Zr, decreasing to 10 -19 m 2 s -1 for the transfer with a subsurface tin impurity.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
NASA NTRS1978

Two-stream theory of spectral reflectance of snow

Spectral reflectance of snow under diffuse illumination is studied using the two-stream approximation of the radiative transfer equation. The scattering and absorption within the snowcover due to the randomly distributed ice grains are characterized by the single scattering albedo and anisotropic phase function. Geometric optics calculations are used to relate the scattering and absorption parameters to grain size and density of snow. Analytical expressions for the intensity within the snowpack and the asymptotic flux extinction coefficient are also obtained. Good agreement is shown between the theory and available experimental data on visible and near-infrared reflectance and asymptotic flux extinction coefficient. The theory also may be used to explain the observed effect of aging on the snow reflectance.

Choudhury, B. J.↗
DOE OSTI2014

Effect of fuel rate and annealing process of LiFePO{sub 4} cathode material for Li-ion batteries synthesized by flame spray pyrolysis method

In this study the effect of fuel rate and annealing on particle formation of LiFePO{sub 4} as battery cathode using flame spray pyrolysis method was investigated numerically and experimentally. Numerical study was done using ANSYS FLUENT program. In experimentally, LiFePO{sub 4} was synthesized from inorganic aqueous solution followed by annealing. LPG was used as fuel and air was used as oxidizer and carrier gas. Annealing process attempted in inert atmosphere at 700°C for 240 min. Numerical result showed that the increase of fuel rate caused the increase of flame temperature. Microscopic observation using Scanning Electron Microscopy (SEM) revealed that all particles have sphere and polydisperse. Increasing fuel rate caused decreasing particle size and increasing particles crystallinity. This phenomenon attributed to the flame temperature. However, all produced particles still have more amorphous phase. Therefore, annealing needed to increase particles crystallinity. Fourier Transform Infrared (FTIR) analysis showed that all particles have PO4 function group. Increasing fuel rate led to the increase of infrared spectrum absorption corresponding to the increase of particles crystallinity. This result indicated that phosphate group vibrated easily in crystalline phase. From Electrochemical Impedance Spectroscopy (EIS) analysis, annealing can cause the increase of Li{sup +} diffusivity. The diffusivity coefficient of without and with annealing particles were 6.84399×10{sup −10} and 8.59888×10{sup −10} cm{sup 2} s{sup −1}, respectively.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
NASA NTRS1993

Polarimetric backscattering from sea ice

Polarimetric backscattering from sea ice is presented. Theoretical models for backscattering are first presented for various ice types. Then, theoretical results are compared with experimental data for new thin ice, first-year ice, and multi-year ice. Sea ice is modeled as a layer medium containing random scatterers and rough interfaces. For multi-year sea ice with snow cover, the sea ice layer is modeled as an ice background with embedded spheroidal air bubbles and the snow layer as air with ice grains. The hummocky topography on multi-year ice is characterized by a Gaussian distribution which has an averaging effect on backscattering coefficients. First-year sea ice is described by an ice medium hosting ellipsoidal brine inclusions. These inclusions are oriented preferentially in the vertical direction due to the columnar structure of first-year sea ice. Azimuthally, the orientation of the brine pockets are random corresponding to the random c-axes in sea ice, unless the axes are oriented by sea currents. For thin ice in newly opened leads, it has been observed that there exists a thin brine layer with very high salinity on the top surface of the new ice. This brine layer is depicted as a medium with high permittivity which can significantly affect electromagnetic scattering signatures from the lower thin ice layer, with a higher fractional volume of brine inclusions due to higher salinity as compared to thick first-year sea ice. The rough medium interfaces are described as Gaussian rough surfaces characterized by root-mean-square heights and surface correlation lengths. The contribution from rough surface, calculated under the Kirchhoff approximation or small perturbation method, is assumed to be independent from volume scattering. The total loss including absorption and scattering losses in the scattering media is represented by the imaginary part of effective permittivity obtained from the strong fluctuation theory. The polarimetric scattering coefficients for different ice types are then derived under the distorted Born approximation.

Nghiem, S. V.↗
DOE OSTI2018

Instability Increments of Stimulated Mandelshtam–Brillouin Scattering in a Bounded Region with Allowance for Collisions

The problem of Mandelstam–Brillouin scattering in the region bounded in the direction of pump wave propagation and infinite in the transverse direction is considered. Such situations can arise, for example, in plasma heating or diagnostic problems. Since the time of scattered radiation escape for the examined geometry upon scattering at a certain angle increases substantially, this effect compensates for a decrease in the nonlinear feedback coefficient upon oblique scattering and leads to instability development. Since the convective losses at scattering angles close to π/2 are small, collisional absorption of waves plays an important role in this case. The instability increments are calculated taking into account not only the convective losses, but also the collisional wave attenuation.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗

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