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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 253 records · Page 14
All sourcesNASA NTRSDOE OSTI
NASA NTRS1980

Saturn's atmospheric temperature structure and heat budget

The effective temperature of Saturn from 30 deg S to 10 deg N is 96.5 + or - 2.5 K. This value is 1.9 K higher than a preliminary estimate (Ingersoll et al., 1980). The atmospheric mole fraction of H2 + He is 90 + or - 3%. This value is derived by comparing infrared and radio occultation data (Kliore et al., 1980) for the same latitude. The high value of the effective temperature suggests that Saturn has an additional energy source besides cooling and contraction. The high mole fraction of H2 suggests that separation of heavier He toward the core may be supplying the additional energy. Atmospheric temperatures in the 60- to 600-mbar range are 2.5 K lower within 7 deg of the equator than at higher latitudes. An almost isothermal layer exists between 60 and 160 mbar at all latitudes.

Orton, G. S.↗
NASA NTRS1986

Analysis of effective radiant temperatures in a Pacific Northwest forest using Thermal Infrared Multispectral Scanner data

Analysis of Thermal Infrared Multispectral Scanner data collected over H. J. Andrews experimental forest in western Oregon indicated that aspect and slope gradient had a greater effect on the thermal emission of younger reforested clearcuts than of older stands. Older forest stands (older than 25 years) with greater amounts of green biomass and closed canopies, had lower effective radiant temperatures than younger, less dense stands. Aspect and slope had little effect on the effective radiant temperature of these older stands. Canopy temperature recorded at approximately 1:30 pm local time July 29, 1983 were nearly equal to maximum daily air temperature recorded at eight reference stands. The investigation provided some insights into the utility of the thermal sensor for detecting surface temperature differences related to forest composition and green biomass amounts in mountain terrain.

Sader, S. A.↗
DOE OSTI2025

A Unified Interpretation of Variability in Precipitation Isotope Ratios

Abstract Several mechanisms have been proposed to explain why the isotope ratios of precipitation vary in space and time and why they correlate with other climate variables like temperature and precipitation. Here, we argue that this behavior is best understood through the lens of radiative transfer, which treats the depletion of atmospheric vapor transport by precipitation as analogous to the attenuation of light by absorption or scattering. Building on earlier work by Siler et al., we introduce a simple model that uses the equations of radiative transfer to approximate the two-dimensional pattern of the oxygen isotope composition of precipitation ( δ p ) from monthly mean hydrologic variables. The model accurately simulates the spatial and seasonal variability in δ p within a state-of-the-art climate model and permits a simple decomposition of δ p variability into contributions from gradients in evaporation and the length scale of vapor transport. Outside the tropics, δ p is mostly controlled by gradients in evaporation, whose dependence on temperature explains the positive correlation between δ p and temperature (i.e., the temperature effect). At low latitudes, δ p is mostly controlled by gradients in the transport length scale, whose inverse relationship with precipitation explains the negative correlation between δ p and precipitation (i.e., the amount effect). This suggests that the temperature and amount effects are both mostly explained by the variability in upstream rainout, but they reflect distinct mechanisms governing rainout at different latitudes. Significance Statement The isotopic composition of precipitation has long been used to make inferences about past climates based on its observed relationship with precipitation in the tropics and with temperature at higher latitudes. These relationships—known as the “amount effect” and “temperature effect,” respectively—have been attributed to many different mechanisms, most of which are thought to operate at either high or low latitudes but not both. Here, we present a unified framework for interpreting the isotope variability that can explain the latitude dependence of the temperature and amount effects despite making no distinction between high and low latitudes. Although our results are generally consistent with certain interpretations of the amount effect, they suggest that the temperature effect is widely misunderstood.

54 ENVIRONMENTAL SCIENCES↗
NASA NTRS1976

An analysis of data related to the minimum temperatures for valid testing in cryogenic wind tunnels using nitrogen as the test gas

The minimum operating temperature which avoids adverse low temperature effects, such as condensation, has been determined at a free stream Mach number of 0.85 for flow over a 0.137 meter airfoil mounted at zero incidence in the Langley 1/3 meter transonic cryogenic tunnel. The onset of low temperature effects is established by comparing the pressure coefficient measured at a given orifice for a particular temperature with those measured at temperatures sufficiently above where low temperature effects might be expected to occur. The pressure distributions over the airfoil are presented in tabular form. In addition, the comparisons of the pressure coefficient as a function of total temperature are presented graphically for chord locations of 0, 25, 50, and 75 percent. Over the 1.2 to 4.5 atmosphere total pressure range investigated, low temperature effects are not detected until total temperatures are 2 K, or more, below free stream saturation temperatures.

Hall, R. M.↗
NASA NTRS1981

The effect of temperature fluctuations of reaction rate constants in turbulent reacting flows

Current models of turbulent reacting flows frequently use Arrhenius reaction rate constants obtained from static or laminar flow theory and/or experiments, or from best fits of static, laminar, and turbulent data. By treating the reaction rate constant as a continuous random variable which is temperature-dependent, the present study assesses the effect of turbulent temperature fluctuations on the reaction rate constant. This model requires that a probability density function (PDF) describing the nature of the fluctuations be specified. Three PDFs are examined: the clipped Gaussian, the beta PDF, and the ramp model. All the models indicate that the reaction rate constant is greater in a turbulent flow field than in an equivalent laminar flow. In addition, an amplification ratio, which is the ratio of the turbulent rate constant to the laminar rate constant, is defined and its behavior as a function of the mean temperature fluctuations is described

Chinitz, W.↗
NASA NTRS1979

Radiative transfer in spherical shell atmospheres. III - Application to Venus

A method for partitioning the radiance emerging from a planetary atmosphere in proportion to the average number of scatterings in each atmospheric layer is applied to Venus in order to account for the various atmospheric levels which contribute to the radiance. A backward Monte Carlo technique is used to calculate core and continuum radiances for the P(16) line of the 8689-A CO2 band for various phase angles and colatitudes in a realistic model of the Venus atmosphere. Effective temperatures for the radiance are defined in two ways, both of which are shown to vary little with phase angles up to 120 deg, and fall rapidly beyond this point, in accordance with spectroscopic results. Temperature increases on the order of 7 K and 10 K are found going from the core of the line to the continuum for colatitudes of 90 and 20 deg, respectively, and the effective temperature is calculated to decrease from equator to pole. An effective optical depth is also defined, which, together with the concepts of effective temperature and effective height, is considered to bring a more fundamental understanding of the concept of level of line formation.

Kattawar, G. W.↗
DOE OSTI2026

Effects of temperature and dose rate on ion-irradiated γ-LiAlO 2 pellets

Defect accumulation and microstructural evolution during ion irradiation at elevated temperatures are governed by competing processes of defect production, driven by the dose rate, and defect recovery, controlled by diffusion, interaction, and annihilation. Here, this study investigates the effects of irradiation temperature and the dose rate on microstructural evolution, deuterium retention, and lithium volatilization in γ-LiAlO 2 pellets subjected to sequential He + and D + ion irradiation. Experiments were performed to a total fluence of 3 × 10 17 (He + + D + )/cm 2 at 623, 673, 723, and 773 K with an average He + dose rate of 7.7 × 10 −4 dpa/s, and to 2 × 10 17 (He + + D + )/cm 2 at 773 K with dose rates of 6.8 × 10 −5 , 2.9 × 10 −4 , and 7.3 × 10 −4 dpa/s. At 623 K, the microstructure was dominated by cavities and fractures with no observable precipitate formation, while small precipitates emerged at 673 K. Increasing the irradiation temperature to 723–773 K promoted the formation of larger, faceted LiAl 5 O 8 precipitates, and surface amorphization, accompanied by pronounced lithium depletion and H–D isotopic exchange. At 773 K, medium and high dose rates produced an amorphized surface layer over a crystalline subsurface containing LiAl 5 O 8 precipitates and blisters at the crystalline–amorphous interface, whereas low-dose-rate irradiation preserved surface crystallinity with cavities distributed in the matrix, around precipitates, and along grain boundaries. Precipitate morphology was anisotropic with limited size dependence on the dose rate. These results elucidate the coupled effects of temperature and the dose rate and demonstrate that sequential He + and D 2 + irradiation at 773 K reproduces key microstructural features and H isotope behavior observed in neutron-irradiated γ-LiAlO 2 at 573 K.

dose rate effects↗
NASA NTRS2006

Fundamental Properties of O-Type Stars

We present a comprehensive analysis of high-resolution, far-ultraviolet HST STIS, FUSE, and optical spectra of 18 O stars in the Small Magellanic Cloud. Our analysis is based on the OSTAR2002 grid of NLTE metal-line-blanketed model atmospheres calculated with our code TLUSTY. We systematically explore and present the sensitivity of various UV and optical lines to different stellar parameters. We have obtained consistent fits of the UV and the optical spectrum to derive the effective temperature, surface gravity, surface composition, and microturbulent velocity of each star. Stellar radii, masses, and luminosities follow directly. For stars of the same spectral subtype, we find a general good agreement between effective temperature determinations obtained with TLUSTY, CMFGEN, and FASTWIND models, which are all lower than the standard T(sub eff) calibration of O stars. We propose a new calibration between the spectral type and effective temperature based on our results from UV metal lines, as well as optical hydrogen and helium lines. The lower effective temperatures translate into ionizing luminosities that are smaller by a factor of 3 compared to luminosities inferred from previous standard calibrations. The chemical composition analysis reveals that the surface of about 80% of the program stars is moderately to strongly enriched in nitrogen, while showing the original helium, carbon, and oxygen abundances. Our results support the new stellar evolution models that predict that the surface of fast rotating stars becomes nitrogen-rich during the main-sequence phase because of rotationally induced mixing. Enrichment factors are, however, larger than predicted by stellar evolution models. Most stars exhibit the "mass discrepancy" problem, which we interpret as a result of fast rotation that lowers the measured effective gravity. Nitrogen enrichment and low spectroscopic masses are therefore two manifestations of fast rotation. Our study thus emphasizes the importance of rotation in our understanding of the properties of massive stars and provides a framework for investigating populations of low-metallicity massive stars at low and high redshifts.

Heap, Sara R.↗
NASA NTRS1995

NASA-UVA Light Aerospace Alloy and Structures Technology program (LA2ST)

The objective of the LA2ST Program is to conduct interdisciplinary graduate student research on the performance of next generation, light-weight aerospace alloys, composites, and thermal gradient structures in collaboration with NASA-Langley researchers. The general aim is to produce relevant data and basic understanding of material mechanical response, environment/corrosion behavior, and microstructure; new monolithic and composite alloys; advanced processing methods; new solid and fluid mechanics analyses; measurement and modeling advances; and a pool of educated students for aerospace technologies. Specific technical objectives are presented for each of the following research projects: time-temperature dependent fracture in advanced wrought ingot metallurgy, and spray deposited aluminum alloys; cryogenic temperature effects on the deformation and fracture of Al-Li-Cu-In alloys; effects of aging and temperature on the ductile fracture of AA2095 and AA2195; mechanisms of localized corrosion in alloys 2090 and 2095; hydrogen interactions in aluminum-lithium alloys 2090 and selected model alloys; mechanisms of deformation and fracture in high strength titanium alloys (effects of temperature and hydrogen and effects of temperature and microstructure); evaluations of wide-panel aluminum alloy extrusions; Al-Si-Ge alloy development; effects of texture and precipitates on mechanical property anisotropy of Al-Cu-Mg-X alloys; damage evolution in polymeric composites; and environmental effects in fatigue life prediction - modeling crack propagation in light aerospace alloys.

Starke, Edgar A., Jr.↗
NASA NTRS2003

Outbursts in Symbiotic Binaries

Two models have been proposed for the outbursts of symbiotic stars. In the thermonuclear model, outbursts begin when the hydrogen burning shell of a hot white dwarf reaches a critical mass. After a rapid increase in the luminosity and effective temperature, the white dwarf evolves at constant luminosity to lower effective temperatures, remains at optical maximum for several years, and then returns to quiescence along a white dwarf cooling curve. In disk instability models, the brightness rises when the accretion rate from the disk onto the central white dwarf abruptly increases by factors of 5-20. After a few month to several year period at maximum, both the luminosity and the effective temperature of the disk decline as the system returns to quiescence.

Mushotzky, Richard↗
NASA NTRS2004

Outbursts in Symbiotic Binaries

Two models have been proposed for the outbursts of symbiotic stars. In the thermonuclear model, outbursts begin when the hydrogen burning shell of a hot white dwarf reaches a critical mass. After a rapid increase in the luminosity and effective temperature, the white dwarf evolves at constant luminosity to lower effective temperatures, remains at optical maximum for several years, and then returns to quiescence along a white dwarf cooling curve. In disk instability models, the brightness rises when the accretion rate from the disk onto the central white dwarf abruptly increases by factors of 5-20. After a few month to several year period at maximum, both the luminosity and the effective temperature of the disk decline as the system returns to quiescence. If most symbiotic stars undergo thermonuclear eruptions, then symbiotics are probably poor candidates for type I supernovae. However, they can then provide approx. 10% of the material which stars recycle back into the interstellar medium. If disk instabilities are the dominant eruption mechanism, symbiotics are promising type Ia candidates but recycle less material into the interstellar medium.

Sonneborn, George↗
NASA NTRS1984

Effect of Temperature on Fiber-Optic Delay

Fiber/jacket interactions affect performance. Attenuation and phase measurements made to assess effect of temperature on signal delay and attenuation in two fiber-optic cable samples.

Bergman, L. A.↗
NASA NTRS1977

Effects of temperature transients at fan inlet of a turbofan engine

The effects of fan inlet temperature transients on the performance and stability of a turbofan engine were determined. The experiment was conducted at 90 and 74 percent of low-pressure-rotor military speed (9525 rpm) and with fan inlet temperature distortions having circumferential extents of 90 deg, 180 deg, 270 deg, and 360 deg. Temperature transients were controlled by varying the magnitude and rate of change of the inlet temperature rise. The engine response ranged from a momentary compressor pressure disturbance to low-pressure-compressor stall. The compressor distortion limits decreased with decreasing low-pressure-rotor speed and increased with increasing circumferential extent of distortion. Analysis of the data suggests strongly that the distortion limits of the compressor are a function of a critical magnitude of inlet temperature rise and are independent of the temperature rise rate.

Abdelwahab, M.↗