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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 199 records · Page 11
All sourcesNASA NTRSDOE OSTI
NASA NTRS1976

Investigation of minimum operating temperatures for cryogenic wind tunnels

Total temperatures corresponding to the onset of condensation effects were determined for flow over a 0.137-m NACA 0012-64 airfoil mounted in the Langley 1/3-m transonic wind tunnel. Tests were carried out at a total pressure range from 1.2 to 4.5 atm and at free-stream Mach numbers of 0.75, 0.85, and 0.95. No condensation effects were found to occur until total temperatures were below those associated with free-stream saturation. Significant increases in Reynolds number may apparently be obtained by operation at wind tunnel temperatures below those associated with local saturation over the airfoil but above those where effects first occur. For the 0.85 and 0.95 Mach numbers the increase in Reynolds number was at least 15% over those achieved at local saturation conditions for the same pressure range. Higher pressures may have had some detrimental effect in the 0.95 Mach number test.

Hall, R. M.↗
NASA NTRS1998

[Sources of Methane in the Boreal Region]

In determining the global methane budget the sources of methane must be balanced with the sinks and atmospheric inventory. The approximate contribution of the different methane sources to the budget has been establish showing the major terrestrial inputs as rice, wetlands, bogs, fens, and tundra. Measurements and modeling of production in these sources suggest that temperature, water table height and saturation along with substratum composition are important in controlling methane production and emission. The isotopic budget of 13 C and D/H in methane can be used as a tool to clarify the global budget. This approach has achieved success at constraining the inputs. Studies using the isotopic approach place constraints on global methane production from different sources. Also, the relation between the two biogenic production pathways, acetate fermentation and CO2 reduction, and the effect of substratum composition can be made using isotope measurements shows the relation between the different biogenic, thermogenic and anthropogenic sources of methane as a function of the carbon and hydrogen isotope values for each source and the atmosphere, tropospheric composition. Methane emissions from ponds and fens are a significant source in the methane budget of the boreal region. An initial study in 1993 and 1994 on the isotopic composition of this methane source and the isotopic composition in relation to oxidation of methane at the sediment surface of the ponds or fen was conducted as part of our BOREAS project. The isotopic composition of methane emitted by saturated anoxic sediment is dependent on the sediment composition and geochemistry, but will be influenced by in situ oxidation, in part, a function of rooted plant activity. The influence of oxidation mediated by rooted plant activities on the isotopic composition of methane is not well known and will depend on the plant type, sediment temperature, and numerous other variables. Information on this isotopic composition is important in both understanding the bio-geochemistry of the system and also in determining the regional and global inputs for the methane isotope budget. In determining the destruction of methane for balancing the atmospheric methane budget soil oxidation must be considered.

Source record↗
NASA NTRS2009

Continuous Lidar Monitoring of Polar Stratospheric Clouds at the South Pole

Polar stratospheric clouds (PSC) play a primary role in the formation of annual ozone holes over Antarctica during the austral sunrise. Meridional temperature gradients in the lower stratosphere and upper troposphere, caused by strong radiative cooling, induce a broad dynamic vortex centered near the South Pole that decouples and insulates the winter polar airmass. PSC nucleate and grow as vortex temperatures gradually fall below equilibrium saturation and frost points for ambient sulfate, nitrate, and water vapor concentrations (generally below 197 K). Cloud surfaces promote heterogeneous reactions that convert stable chlorine and bromine-based molecules into photochemically active ones. As spring nears, and the sun reappears and rises, photolysis decomposes these partitioned compounds into individual halogen atoms that react with and catalytically destroy thousands of ozone molecules before they are stochastically neutralized. Despite a generic understanding of the ozone hole paradigm, many key components of the system, such as cloud occurrence, phase, and composition; particle growth mechanisms; and denitrification of the lower stratosphere have yet to be fully resolved. Satellite-based observations have dramatically improved the ability to detect PSC and quantify seasonal polar chemical partitioning. However, coverage directly over the Antarctic plateau is limited by polar-orbiting tracks that rarely exceed 80 degrees S. In December 1999, a NASA Micropulse Lidar Network instrument (MPLNET) was first deployed to the NOAA Earth Systems Research Laboratory (ESRL) Atmospheric Research Observatory at the Amundsen-Scott South Pole Station for continuous cloud and aerosol profiling. MPLNET instruments are eye-safe, capable of full-time autonomous operation, and suitably rugged and compact to withstand long-term remote deployment. With only brief interruptions during the winters of 2001 and 2002, a nearly continuous data archive exists to the present.

OZONE DESTRUCTION↗
NASA NTRS1976

Magnetic field generated resistivity maximum in graphite

In a zero magnetic field, the electrical resistivity of highly oriented pyrolytic (polycrystalline) graphite drops smoothly with decreasing temperature, becoming constant below 4 K. However, in a fixed applied magnetic field, the resistivity goes through a maximum as a function of temperature, with a larger maximum for a larger field intensity. The temperature of the maximum increases with field intensity, but saturates to a constant value near 25 K (the exact temperature depends on the sample) at high intensity. In single-crystal graphite, a maximum in resistivity as a function of temperature is also present, but has the effects of Landau level quantization superimposed. Several possible explanations for the resistivity maximum are proposed, but a complete explanation awaits detailed calculations involving the energy band structure of graphite, and the particular scattering mechanisms involved.

Woollam, J. A.↗
NASA NTRS1978

Meteorological radar calibration

A meteorological radar calibration technique is developed. It is found that the integrated, range corrected, received power saturates under intense rain conditions in a manner analogous to that encountered for the radiometric path temperature. Furthermore, it is found that this saturation condition establishes a bound which may be used to determine an absolution radar calibration for the case of radars operating at attenuating wavelengths. In the case of less intense rainfall or for radars at nonattenuating wavelengths, the relationship for direct calibration in terms of an independent measurement of radiometric path temperature is developed. This approach offers the advantage that the calibration is in terms of an independent measurement of the rainfall through the same elevated region as that viewed by the radar.

Hodge, D. B.↗
NASA NTRS1973

Magnetic properties of Dy2Ti2O7

Measurements were made of the magnetization, differential magnetic susceptibility, and magnetic entropy of powered samples of Dy2Ti2O7. The saturation magnetic moment is 4.7 + or - 0.2 Bohr magnetons per Dy ion, instead of 10 as predicted by Hund's rules. A temperature-independent magnetization is observed in the saturation region. Absolute values of magnetic entropy have been obtained for temperatures from 1.25 to 20 K, in applied fields up to 10.4 tesla. The magnetic entropy approaches a maximum value consistent with a ground-state multiplicity of 2. Low field magnetization and differential susceptibility data show a transition to antiferromagnetism near 1.35 K. A construction of the magnetic specific heat from the zero field entropy shows an anomaly near the same temperature.

Flood, D. J.↗
NASA NTRS1996

Development and Utility of a Four-Channel Scanner for Wildland Fire Research and Applications

The Airborne Infrared Disaster Assessment System (AIRDAS) is a four-channel scanner designed and built at NASA-Ames for the specific task of supporting research and applications on fire impacts on terrestrial and atmospheric processes and also of serving as a vital instrument in the assessment of natural and man-induced disasters. The system has been flown on numerous airframes including the Navajo, King-Air, C0130, and Lear Jet 310 and a 206. The system includes a configuration composed of a 386 PC computer workstation, a non-linear detector amplifier, a sixteen-bit digitizer, dichroic filters, and Exabyte 8500 5Gb Tape output, VHS tape output, a Rockwell GPS and a 2-axis gyro. The AIRDAS system collects digital data in four wavelength regions, which can be filtered: band 1 (0.61-0.68 microns), band 2 (1.57-1.7 microns), band 3 (3.6-5.5 microns), and band 4 (5.5-13.0 microns), an FOV of 108 degrees, an IFOV of 2.62 mrads, and a digitized swath width of 720 pixels. The inclusion of the non-linear detector amplifier allows for the accurate measurement of emitted temperature from fires and hot spots. Lab testing of the scanner has indicated temperature assessments of 800 C without detector saturation. This has advantages over previous systems which were designed for thermal measurement of earth background temperatures, and were ill-equipped for accurate determination of high intensity conditions. The scanner has been flown successfully on data collection missions since 1992 in the western US as well as Brazil. These and other research and applications responses will be presented along with an assessment of future directions with the system.a

Ambrosia, Vincent G.↗
NASA NTRS1981

Application of thermal model for pan evaporation to the hydrology of a defined medium, the sponge

A technique is presented which estimates pan evaporation from the commonly observed values of daily maximum and minimum air temperatures. These two variables are transformed to saturation vapor pressure equivalents which are used in a simple linear regression model. The model provides reasonably accurate estimates of pan evaporation rates over a large geographic area. The derived evaporation algorithm is combined with precipitation to obtain a simple moisture variable. A hypothetical medium with a capacity of 8 inches of water is initialized at 4 inches. The medium behaves like a sponge: it absorbs all incident precipitation, with runoff or drainage occurring only after it is saturated. Water is lost from this simple system through evaporation just as from a Class A pan, but at a rate proportional to its degree of saturation. The contents of the sponge is a moisture index calculated from only the maximum and minium temperatures and precipitation.

Trenchard, M. H.↗
NASA NTRS1982

Stable Stratification for Solar Ponds

Stable density gradient forms in pond saturated with disodium phosphate (DSP). Volume of DSP saturated water tends to develop temperature and density layers. Since tests indicate thermal and density gradients remain in equilibrium at heat removal rates of 60 percent or more of heat input rate, pond containing DSP would be suitable for collecting solar energy and transferring it to heat exchanger for practical use.

Mehta, G. D.↗
NASA NTRS1982

An experimental investigation of the vaporous/gaseous cavity characteristics of an eccentric journal bearing

This paper describes the experimental pressure and temperature results obtained when rotating a shaft in an eccentric lucite casing at velocities ranging from 209 to 628 rad/s (2000 to 6000 rpm). The results are presented in terms of three-dimensional plots and contour maps. Photographic evidence is presented to illustrate how the downstream and upstream regions of the cavity develop and evolve into the well-known finger patterns. A comparison between pressure and temperature profiles in air-saturated oil and carbon dioxide-saturated oil is presented; the origin and nature of the gases contained in the cavity are discussed. Three analytical models (Swift-Stieber, separation, Floberg) predicting the formation of the cavitation zone are presented and evaluated in light of the experimental results. A motion-picture supplement depicting these results is available upon request.

Braun, M. J.↗
NASA NTRS1989

Polyimide Matrix composites: Polyimidesulfone/LARC-TPI (1:1) blend

Polyimide matrix composites were fabricated from unidirectional unsized AS-4 carbon fiber and a doped 1:1 blend of two polyimides: benzophenone dianhydride-3,3'-diamino diphenylsulfone (PISO2) and benzophenone dianhydride-3,3'-diamino benzophenone (LARC-TPI). To enhance melt flow properties, the molecular weight of the PISO2 was controlled by end-capping with phthalic anhydride and addition of 5 percent by weight p-phenylene diamine-phthalic anhydride bisamic acid dopant. Prepreg was drum-wound using a diglyme slurry comprised of the soluble polyamideacid of PISO2, the soluble bisamideacid of the dopant, and the insoluble imidized LARC-TPI powder. Melt flow studies with a rotary rheometer and parallel plate plastometer on neat resin and prepreg helped develop an optimum cure cycle. Composite mechanical properties at room and elevated temperatures, dry and moisture-saturated, were evaluated, including short beam shear strength and flexure, tensile, shear, and compression properties. Two 18 in. x 24 in. skin-stringer panels were fabricated, one of which was tested in compression to failure.

Johnston, Norman J.↗
NASA NTRS1989

Polyimide matrix composites - Polyimidesulfone/LARC-TPI (1:1) blend

Polyimide matrix composites were fabricated from unidirectional unsized AS-4 carbon fiber and a doped 1:1 blend of two polyimides: PISO2 and LARC-TPI. To enhance melt flow properties, the molecular weight of the PISO2 was controlled by end-capping with phthalic anhydride and addition of 5 percent by weight p-phenylenediamine-phthalic anhydride bisamic acid dopant. Prepreg was drum-wound using a diglyme slurry comprised of the soluble polyamideacid of PISO2, the soluble bisamideacid of the dopant, and the insoluble imidized LARC-TPI powder. Melt flow studies with a rotary rheometer and parallel plate plastometer on neat resin and prepreg helped develop an optimum cure cycle. Composite mechanical properties at room and elevated temperatures, dry and moisture-saturated, were evaluated, including short beam shear strength and flexure, tensile, shear, and compression properties. Two 18 x 24-inch skin-stringer panels were fabricated, one of which was tested in compression to failure.

Johnston, Norman J.↗
NASA NTRS1990

The sensitivity of latent heat flux to the air humidity approximations used in ocean circulation models

In deriving the surface latent heat flux with the bulk formula for the thermal forcing of some ocean circulation models, two approximations are commonly made to bypass the use of atmospheric humidity in the formula. The first assumes a constant relative humidity, and the second supposes that the sea-air humidity difference varies linearly with the saturation humidity at sea surface temperature. Using climatological fields derived from the Marine Deck and long time series from ocean weather stations, the errors introduced by these two assumptions are examined. It is shown that the errors reach above 100 W/sq m over western boundary currents and 50 W/sq m over the tropical ocean. The two approximations also introduce erroneous seasonal and spatial variabilities with magnitudes over 50 percent of the observed variabilities.

Liu, W. Timothy↗
NASA NTRS1993

Quartz dissolution. I - Negative crystal experiments and a rate law. II - Theory of rough and smooth surfaces

The range of the measured quartz dissolution rates, as a function of temperature and pOH, extent of saturation, and ionic strength, is extended to cover a wider range of solution chemistries, using the negative crystal methodology of Gratz et al. (1990) to measure the dissolution rate. A simple rate law describing the quartz dissolution kinetics above the point of zero charge of quartz is derived for ionic strengths above 0.003 m. Measurements were performed on some defective crystals, and the mathematics of step motion was developed for quartz dissolution and was compared with rough-face behavior using two different models.

Gratz, Andrew J.↗
NASA NTRS1993

Reverse polarity magnetized melt rocks from the Chicxulub impact structure, Yucatan Peninsula, Mexico

Further paleomagnetic data for core samples of melt rock recovered in the Petroleos Mexicanos (PEMEX) exploratory wells within the Chicxulub structure, northern Yucatan peninsula, Mexico are reported. A previous report by Sharpton showed that the rocks studied contain high iridium levels and shocked breccia clasts, and an Ar-40/Ar-39 age of 65.2 plus or minus 0.4 Ma. The geomagnetic polarity determined for two samples is reverse (R) and was correlated with chron 29R that includes the K/T boundary. Our present analysis is based on two samples from each of three clasts of the melt rock from PEMEX well Y6-N17 (1295 to 1299 m b.s.l.). This study concentrates on the vectorial nature and stability of the remanence (NRM), the magnetic mineralogy and remanence carriers (i.e., the reliability and origin of the record), and on the implications (correlation with expected paleolatitude and polarity). The relative orientation of the drill core samples with respect to the horizontal is known. Samples were stable under alternating field (AF) and thermal treatments, and after removal of a small component they exhibited single-vectorial behavior. The characteristic remanence inclinations show small dispersion and a mean value (-43 deg) in close agreement with the expected inclination and paleolatitude (derived from the North American apparent polar wander path). Isothermal remenence (IRM) acquisition experiments, Lowrie-Fuller tests, coercivity and unblocking temperature spectra of NRM and saturation IRM, susceptibility and Q-coefficient analyses, and the single-component nature indicate a dominant mineralogy of iron-rich titanomagnetites with single or pseduo-single domain states. The stable characteristic magnetization may be interpreted as a result of shock heating of the rock at the time of formation of the inpact structure and its polarity, age, and paleolatitude are consistent with a time about the K/T boundary.

Urrutia-Fucugauchi, Jaime↗
NASA NTRS1993

Laser-saturated fluorescence measurements in laminar sooting diffusion flames

The hydroxyl radical is known to be one of the most important intermediate species in the combustion processes. The hydroxyl radical has also been considered a dominant oxidizer of soot particles in flames. In this investigation the hydroxyl concentration profiles in sooting diffusion flames were measured by the laser-saturated fluorescence (LSF) method. The temperature distributions in the flames were measured by the two-line LSF technique and by thermocouple. In the sooting region the OH fluorescence was too weak to make accurate temperature measurements. The hydroxyl fluorescence profiles for all four flames presented herein show that the OH fluorescence intensities peaked near the flame front. The OH fluorescence intensity dropped sharply toward the dark region of the flame and continued declining to the sooting region. The OH fluorescence profiles also indicate that the OH fluorescence decreased with increasing height in the flames for all flames investigated. Varying the oxidizer composition resulted in a corresponding variation in the maximum OH concentration and the flame temperature. Furthermore, it appears that the maximum OH concentration for each flame increased with increasing flame temperature.

Wey, Changlie↗