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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 OSTI2019

Evaluation of Alternative Designs for a High Temperature Particle-to-sCO 2 Heat Exchanger

This paper presents an evaluation of alternative particle heat-exchanger designs, including moving packed-bed and fluidized-bed designs, for high-temperature heating of a solar-driven supercritical CO 2 (sCO 2 ) Brayton power cycle. The design requirements for high pressure (=20 MPa) and high temperature (=700 °C) operation associated with sCO 2 posed several challenges requiring high-strength materials for piping and/or diffusion bonding for plates. Designs from several vendors for a 100 kW-thermal particle-to-sCO 2 heat exchanger were evaluated as part of this project. Cost, heat-transfer coefficient, structural reliability, manufacturability, parasitics and heat losses, scalability, compatibility, erosion and corrosion, transient operation, and inspection ease were considered in the evaluation. An analytic hierarchy process was used to weight and compare the criteria for the different design options. The fluidized-bed design fared the best on heat transfer coefficient, structural reliability, scalability, and inspection ease, while the moving packed-bed designs fared the best on cost, parasitics and heat losses, manufacturability, compatibility, erosion and corrosion, and transient operation. A 100 kWt shell-and-plate design was ultimately selected for construction and integration with Sandia's falling particle receiver system.

14 SOLAR ENERGY↗
NASA NTRS2011

Synergism of Saturn, Enceladus and Titan and Formation of HCNO Prebiotic Molecules

Saturn as a system has two very exotic moons Titan and Enceladus. Titan, taking in energy from Saturn's magnetosphere, solar UV irradiation, and cosmic rays, can make HCN based molecules as discussed in earlier paper by Raulin and Owen. Space radiation effects at both moons, and as coupled by the Saturn magnetosphere, could cause an unexpected series of events potentially leading to prebiotic chemical evolution at Titan with HCNO from magnetospheric oxygen as the new ingredient. The "Old Faithful" model suggests that Enceladus, highly irradiated by Saturn magnetospheric electrons and thus having a source of chemical energy from radiolytic gas production, has episodic ejections of water vapor, carbon dioxide, and various hydrocarbons into Saturn's magnetosphere. The hydrocarbons do not survive transport through the plasma environment, but oxygen ions from Enceladus water molecules become the dominant ion species in the outer magnetosphere. At Titan, Cassini discovered that 1) keV oxygen ions, evidently from Enceladus, are bombarding Titan's upper atmosphere and 2) heavy positive and negative ions exist in significant abundances within Titan's upper atmosphere. Initial models of heavy ion formation in Titan's upper atmosphere invoked polymerization of aromatics such as benzenes and their radicals to make polycyclic aromatic hydrocarbons (PAH) , while a more recent model by Sittler et al., has raised the possibility of carbon chains forming from the polymerization of acetylene and its radicals to make fullerenes. Laboratory measurements indicate that fullerenes, which are hollow carbon shells, can trap keV oxygen ions. Clustering of the fullerenes with aerosol mixtures from PAHs and the dominant nitrogen molecules could form larger aerosols enriched in trapped oxygen. Aerosol precipitation could then convey these chemically complex structures deeper into the atmosphere and to the moon surface. Ionizing solar UV, magnetospheric electron, and galactic cosmic ray irradiation would provide further energy for processing into more complex organic forms. Further ionizing irradiation from cosmic rays deep in the atmosphere "tho lin" molecules are produced with all the molecular components present from which prebiotic organic molecules can form. This synergy of Saturn system, exogenic irradiation, and molecular processes provides a potential pathway for accumulation of prebiotic chemistry on the surface of Titan. Since fullerenes are also thought to exist in interstellar space, similar processes may also occur there to seed molecular clouds with prebiotic chemical species. We will also discuss possible future laboratory experiments that could be done to investigate fullerene formation at Titan and the trapping of oxygen in fullerenes.

Sittler, Edward C.↗
DOE OSTI2016

TRANSPORT AND MIXING OF r -PROCESS ELEMENTS IN NEUTRON STAR BINARY MERGER BLAST WAVES

The r -process nuclei are robustly synthesized in the material ejected during neutron star binary mergers (NSBMs). If NSBMs are indeed solely responsible for the solar system r -process abundances, a galaxy like our own would be required to host a few NSBMs per million years, with each event ejecting, on average, about 5 × 10{sup −2} M {sub ⊙} of r -process material. Because the ejecta velocities in the tidal tail are significantly larger than those in ordinary supernovae, NSBMs deposit a comparable amount of energy into the ISM. In contrast to extensive efforts studying spherical models for supernova remnant evolution, calculations quantifying the impact of NSBM ejecta in the ISM have been lacking. To better understand their evolution, we perform a suite of three-dimensional hydrodynamic simulations of isolated NSBM ejecta expanding in environments with conditions adopted from Milky-Way-like galaxy simulations. Although the remnant morphology is highly complex at early times, the subsequent radiative evolution is remarkably similar to that of a standard supernova. This implies that sub-resolution supernova feedback models can be used in galaxy-scale simulations that are unable to resolve the key evolutionary phases of NSBMs. Among other quantities, we examine the radius, mass, and kinetic energy content of the remnant at shell formation. We find that the shell formation epoch is attained when the swept-up mass is about 10{sup 3}( n {sub H}/1 cm{sup −3}){sup −2/7} M {sub ⊙;} at this point, the mass fraction of r -process material is enhanced up to two orders of magnitude in relation to a solar metallicity ISM.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2020

Excluded-volume model for quarkyonic matter. II. Three-flavor shell-like distribution of baryons in phase space

We extend the excluded-volume model of isospin symmetric two-flavor dense quarkyonic matter [Phys. Rev. C 101, 035201 (2020)] including strange particles and address its implications for neutron stars. The effective sizes of baryons are defined from the diverging hard-core potentials in the short interdistance regime. Around the hard-core density, the repulsive core between baryons at short distances leads to a saturation in the number density of baryons and generates perturbative quarks from the lower phase space, which leads to the shell-like distribution of baryons by the Pauli exclusion principle. The strange-quark Fermi sea always appears at high densities but the Λ hyperon shell only appears when the effective size of the Λ hyperon is smaller than the effective size of nucleons. We find that the pressure of strange quarkyonic matter can be large enough to support neutron stars with two times solar mass and can have a large sound speed, $c^2_s ≃ 0.7$. Finally, the fraction of the baryon number carried by perturbative quarks is about 30% at the inner core of most massive neutron stars.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
NASA NTRS1974

Radiation damage and structure recorded at high resolution in grains from fine fractions of Luna 16 surface material

Samples returned to earth by Luna 16, were studied with a high voltage electron microscope for ultramicroscopic features. The following amazing features were noted in particles of surface material returned in all the lunar trips: A very high density of tracks of nuclear particles, ultrathin amorphous shells, highly rounded forms, and amazingly good ordering of crystal lattice. These features were used along with calibration experiments in solving the following problems: (1) determining the energy spectrum and chemical abundances of the very heavy nuclei in the solar wind and in the solar cosmic rays; (2) studying the past activity of the sun; (3) obtaining data on lunar dynamic processes affecting dust particles; (4) analyzing composite effects caused by penetration of solar wind into the lunar surface material; and (5) establishing the existence of the ancient lunar atmosphere and magnetic field.

Durrieu, L.↗
NASA NTRS1978

Helium-burning flashes on an accreting neutron star - A model for X-ray burst sources

Detailed numerical models of X-ray bursts resulting from thermonuclear flashes near the surface of an accreting neutron star have been constructed. The models assume a nonrotating nonmagnetized spherically accreting neutron star of 1.4 solar masses, radius 6.6 km, core temperature in the range from 250 million to 570 million K, and accretion rate in the range (0.3-3) x 10 to the 17th power g/s. Under many conditions the helium-burning shell undergoes thermonuclear flashes that result in the emission of X-ray bursts, the gross properties of which are remarkably similar to those of most observed X-ray burst sources. Neutron stars with moderately low core temperatures, low accretion rates, and weak magnetic fields are most likely to produce X-ray bursts.

Joss, P. C.↗
DOE OSTI2014

Baroclinic instability in the solar tachocline

The solar tachocline is likely to be close to a geostrophic 'thermal wind', for which the Coriolis force associated with differential rotation is closely balanced by a latitudinal pressure gradient, leading to a tight relation between the vertical gradient of rotation and the latitudinal entropy gradient. Using a hydrostatic but nongeostrophic spherical shell model, we examine baroclinic instability of the tachocline thermal wind. We find that both the overshoot and radiative parts of the tachocline should be baroclinicly unstable at most latitudes. Growth rates are roughly five times higher in middle and high latitudes compared to low latitudes, and much higher in the overshoot than in the radiative tachocline. They range in e-folding amplification from 10 days in the high latitude overshoot tachocline, down to 20 yr for the low latitude radiative tachocline. In the radiative tachocline only, longitudinal wavenumbers m = 1, 2 are unstable, while in the overshoot tachocline a much broader range of m are unstable. At all latitudes and with all stratifications, the longitudinal scale of the most unstable mode is comparable to the Rossby deformation radius, while the growth rate is set by the local latitudinal entropy gradient. Baroclinic instability in the tachocline competing with instability of the latitude rotation gradient established in earlier studies should be important for the workings of the solar dynamo and should be expected to be found in most stars that contain an interface between radiative and convective domains.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2017

A Suzaku View of Accretion-powered X-Ray Pulsar GX 1+4

We present results obtained from a Suzaku observation of the accretion-powered X-ray pulsar GX 1+4. A broadband continuum spectrum of the pulsar was found to be better described by a simple model consisting of a blackbody component and an exponential cutoff power law than the previously used compTT continuum model. Though the pulse profile had a sharp dip in soft X-rays (<10 keV), phase-resolved spectroscopy confirmed that the dimming was not due to an increase in photoelectric absorption. Phase-sliced spectral analysis showed the presence of a significant spectral modulation beyond 10 keV except for the dip phase. A search for the presence of a cyclotron resonance scattering feature in the Suzaku spectra yielded a negative result. Iron K-shell (K{sub α} and K{sub β}) emission lines from nearly neutral iron ions (<Fe iii) were clearly detected in the source spectrum. A significant K{sub α} emission line from almost neutral Ni atoms was detected for the first time in this source. We estimated an iron abundance of ∼80% of the solar value and an Ni/Fe abundance ratio of about two times the solar value. We searched for an iron Ly{sub α} emission line and found a significant improvement in the spectral fitting by inclusion of this line. We found a clear intensity modulation of the iron K{sub α} line with the pulse phase with an amplitude of 7%. This finding favored an inhomogeneous fluorescent region with a radius much smaller than the size (∼3 × 10{sup 12} cm) estimated by an assumption of homogeneous matter.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2012

DETERMINATION OF THE HELIOSPHERIC RADIAL MAGNETIC FIELD FROM THE STANDOFF DISTANCE OF A CME-DRIVEN SHOCK OBSERVED BY THE STEREO SPACECRAFT

We report on the determination of radial magnetic field strength in the heliocentric distance range from 6 to 120 solar radii (R {sub Sun }) using data from Coronagraph 2 (COR2) and Heliospheric Imager I (HI1) instruments on board the Solar Terrestrial Relations Observatory spacecraft following the standoff-distance method of Gopalswamy and Yashiro. We measured the shock standoff distance of the 2008 April 5 coronal mass ejection (CME) and determined the flux-rope curvature by fitting the three-dimensional shape of the CME using the Graduated Cylindrical Shell model. The radial magnetic field strength is computed from the Alfven speed and the density of the ambient medium. We also compare the derived magnetic field strength with in situ measurements made by the Helios spacecraft, which measured the magnetic field at the heliocentric distance range from 60 to 215 R {sub Sun }. We found that the radial magnetic field strength decreases from 28 mG at 6 R {sub Sun} to 0.17 mG at 120 R {sub Sun }. In addition, we found that the radial profile can be described by a power law.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2017

Plasma measurements of the Fe XVII L-shell emission and blending with F VIII and F IX

We measured the L-shell emission spectrum of Fe XVII in a low-density, low-gradient magnetically confined laboratory plasma that contains predominantly C, O, Fe, and Ni as trace elements and find excellent agreement with the relative spectral emission obtained in solar and astrophysical observations. However, we obtained spectra that appear to have an usually large 1s^22s^22p^5_{1/2}3d_{3/2} --> 1s^22s^22p^6 Fe XVII resonance transition, commonly labeled 3C, from hot plasmas that also contain F. The wavelength of the Ly-alpha feature of F IX is coincident with the wavelength of the Fe XVII line 3C within one part in 538, and its flux, therefore, enhances the Fe XVII resonance line. Moreover, the resonance and forbidden lines of F VIII are close to the 3s --> 2p transitions in Fe XVII, and may further alter the inferred apparent Fe XVII line ratios, particularly in spectrometers with moderate spectral resolution. The enhanced emission of line 3C, thus, can serve as a new spectral diagnostic for the detection of fluorine in astrophysical plasmas.

Atomic processes↗
DOE OSTI2017

Plasma Measurements of the Fe xvii L-shell Emission and Blending with F viii and F ix

Here, we measured the L-shell emission spectrum of Fe xvii in a low-density, low-gradient magnetically confined laboratory plasma that contains predominately C, O, Fe, and Ni as trace elements and found excellent agreement with the relative spectral emission obtained in solar and astrophysical observations. However, we obtained spectra that appear to have an usually large $1{s}^{2}2{s}^{2}2{p}_{1/2}^{5}3{d}_{3/2}\to 1{s}^{2}2{s}^{2}2{p}^{6}$ Fe xvii resonance transition, which is commonly labeled $3C$, from hot plasmas that also contain fluorine. The wavelength of the Lyα feature of F ix is coincident with the wavelength of the Fe xvii line $3C$ within one part in 538, and its flux, therefore, enhances the Fe xvii resonance line. Moreover, the resonance and forbidden lines of F viii are close to the $3s\to 2p$ transitions in Fe xvii and may further alter the inferred apparent Fe xvii line ratios, particularly in spectrometers with moderate spectral resolution. The enhanced emission of line $3C$ can thus serve as a new spectral diagnostic for the detection of fluorine in astrophysical plasmas.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
NASA NTRS1978

Thermal limit for spherical accretion and X-ray bursts

A mechanism is described whereby the rate of spherical accretion on a collapsed object and the resulting X-ray luminosity can be limited by thermal heating and evaporation of the accreting gas. The luminosity limit can be a factor of the order of 100 below the corresponding Eddington limit. Steady accretion flow is not possible within a range above this limit, and X-ray bursts can be produced by accretion surges resulting from the cooling and collapse of a heated gas shell above a critical optical depth. The luminosity and approximate recurrence rate of the bursts from NGC 6624 and other burst sources may then be understood. A general model for bursters is proposed in which massive (about 10 to 100 solar masses) black holes, from massive stars and the cores of disrupted globular clusters, undergo supercritical spherical accretion in interstellar clouds. Both X-ray and gamma-ray bursts are predicted to have similar hard X-ray (about 200 keV) spectra, though high average accretion rates and central optical depths also yield a comparable luminosity at around 5 keV from a Comptonized blackbody spectrum in the X-ray bursts and associated steady sources.

Grindlay, J. E.↗
NASA NTRS1988

Observations of energetic oxygen and carbon ions with charge states between 3 and 6 in the magnetosphere

Data obtained by the AMPTE/CCE charge-energy-mass spectrometer are used to study the average spatial distributions of oxygen and carbon ions with charge states between 3 and 6. The O(6+) and C(6+) ion fluxes are found to increase with the drift shell parameter L up to a constant level at L of not less than 7. It is suggested that the diurnal variations noted are related to the shape of the L profiles. The results support a model in which the solar wind origin O(6+) and C(6+) ions and the terrestrial origin O(+) and O(2+) ions are transported from the tail towards the earth. Charge exchange processes near the earth produce the oxygen and carbon ions with charge states between 3 and 5.

Kremser, G.↗
DOE OSTI2014

A high-entropy-wind r-process study based on nuclear-structure quantities from the new finite-range droplet model FRDM(2012)

Attempts to explain the source of r-process elements in our solar system (S.S.) by particular astrophysical sites still face entwined uncertainties, stemming from the extrapolation of nuclear properties far from stability, inconsistent sources of different properties (e.g., nuclear masses and β-decay properties), and the poor understanding of astrophysical conditions, which are hard to disentangle. In this paper we present results from the investigation of r-process in the high-entropy wind (HEW) of core-collapse supernovae (here chosen as one of the possible scenarios for this nucleosynthesis process), using new nuclear-data input calculated in a consistent approach, for masses and β-decay properties from the new finite-range droplet model FRDM(2012). The accuracy of the new mass model is 0.56 MeV with respect to AME2003, to which it was adjusted. We compare the new HEW r-process abundance pattern to the latest S.S. r-process residuals and to our earlier calculations with the nuclear-structure quantities based on FRDM(1992). Substantial overall and specific local improvements in the calculated pattern of the r-process between A ≅ 110 and {sup 209}Bi, as well as remaining deficiencies, are discussed in terms of the underlying spherical and deformed shell structure far from stability.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2018

Evaluation of Alternative Designs for a High Temperature Particle-to-SCO2 Heat Exchanger

This paper presents an evaluation of alternative particle heat-exchanger designs, including moving packed-bed and fluidized-bed designs, for high-temperature heating of a solar-driven supercritical CO2 (sCO2) Brayton power cycle. The design requirements for high pressure (= 20 MPa) and high temperature (= 700 degrees C) operation associated with sCO2 posed several challenges requiring high-strength materials for piping and/or diffusion bonding for plates. Designs from several vendors for a 100 kW-thermal particle-to-sCO2 heat exchanger were evaluated as part of this project. Cost, heat-transfer coefficient, structural reliability, manufacturability, parasitics and heat losses, scalability, compatibility, erosion and corrosion, transient operation, and inspection ease were considered in the evaluation. An analytical hierarchy process was used to weight and compare the criteria for the different design options. The fluidized-bed design fared the best on heat transfer coefficient, structural reliability, scalability and inspection ease, while the moving packed-bed designs fared the best on cost, parasitics and heat losses, manufacturability, compatibility, erosion and corrosion, and transient operation. A 100 kWt shell-and-plate design was ultimately selected for construction and integration with Sandia's falling particle receiver system.

14 SOLAR ENERGY↗
NASA NTRS1982

High-temperature ceramic heat exchanger element for a solar thermal receiver

A study has been completed on the development of a high-temperature ceramic heat exchanger element to be integrated into a solar reciver producing heated air. A number of conceptual designs were developed for heat exchanger elements of differing configuration. These were evaluated with respect to thermal performance, pressure drop, structural integrity, and fabricability. The final design selection identified a finned ceramic shell as the most favorable concept. The ceramic shell is surrounded by a larger metallic shell. The flanges of the two shells are sealed to provide a leak-tight pressure vessel. The ceramic shell is fabricated by an innovative combination of slip casting the receiver walls and precision casting the heat transfer finned plates. The fins are bonded to the shell during firing. Fabrication of a one-half scale demonstrator ceramic receiver has been completed.

Strumpf, H. J.↗
NASA NTRS2001

Multiwavelength Modeling of Nove Atmospheres

LMC 1988 #1 was a slow, CO type, dust forming classical nova. It was the first extragalactic nova to be observed with the IUE satellite. We have successfully fitted observed ultraviolet and optical spectra of LMC 1988 #1 taken within the first two months of its outburst (when the atmosphere was still optically thick) with synthetic spectra computed using PHOENIX nova model atmospheres. The synthetic spectra reproduce most of the features seen in the spectra and provide V band magnitudes consistent with the observed light curve. The fits are improved by increasing the CNO abundances to 10 times the solar values. The bolometric luminosity of LMC 1988 #1 was approximately constant at 2 x 10(exp 38) ergs per second at a distance of 47.3 kpc for the first 2 months of the outburst until the formation of the dust shell.

Huschildt, P. H.↗