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At least 289 records · Page 16
All sourcesNASA NTRSDOE OSTI
NASA NTRS1977

High temperature environmental effects on metals

The gas turbine engine was used as an example to predict high temperature environmental attack on metals. Environmental attack in a gas turbine engine derives from high temperature, combustion products of the air and fuel burned, and impurities. Of all the modes of attack associated with impurity effects, hot corrosion was the most complicated mechanistically. Solutions to the hot corrosion problem were sought semi-empirically in: (1) improved alloys or ceramics; (2) protective surface coating; (3) use of additives to the engine environment; and (4) air/fuel cleanup to eliminate harmful impurities.

Grisaffe, S. J.↗
NASA NTRS1964

Variable-transparency wall regulates temperatures of structures

An effective temperature regulating wall consists of one layer /e.g., one of the paraffins/ relatively opaque to thermal radiation in the solid state and transparent to it in the molten state and placed between two transparent layers. A mirror coating is applied to back layer.

Osullivan, W. J., Jr.↗
NASA NTRS1994

UV extinction and IR emission in diffuse H2 regions

During this period, much work was spent in an attempt to use theoretical UV line indices as a basis for spectral calibration of the program stars. Five line indices are shown as functions of effective temperature and log g, calculated with the spectral synthesis programs of Kurucz. Open stars and circles are observed values from Fanelli et al., using the spectral class-effective temperature calibration of Schmidt-Kaler. We conclude that these line indices may be used to determine an effective stellar temperature, but with uncertainties of approximately a few thousand degrees. Also, for the hotter stars, theoretical line opacities are systematically low compared to observations. We have also found that Kurucz's new models appear to represent hot stars very well, even at far-UV wavelengths. This is shown in an example where two spectra of mu Col (spectral class 09.5 V) are compared to a synthetic spectrum for T(sub eff) = 33,000 K, log g = 4.0. Also shown (uppermost curve) is an empirical estimate of the intrinsic flux distribution for 09.5 V stars from Papaj, Wegner, and Krelowski.

Aannestad, Per A.↗
NASA NTRS1979

Combined pressure and temperature distortion effects on internal flow of a turbofan engine

The flow characteristics obtained experimentally for the compression of a 2-spool TF30-P-3 turbofan engine operating with 180 grad combined pressure and temperature distortion in the inlet flow are presented. The analytical model (Mazzawy and Banks, 1976), 'tuned' during Lewis testing, was used for pretest predictions of the effects that these distortions would have on the engine flow characteristics and the limiting distortion values. The effect of inlet flow distortion on the performance of the engine is discussed, including: (1) the flow between a screen mounted in the inlet duct and the inlet guide vanes; (2) the flow through the compression system; and (3) the effects of the combined distortion and its orientation on the compressor stability limits. It is concluded that the model used in this program was capable of predicting the effects of total pressure, total temperature and combined total pressure-total temperature distortions in terms of flow profiles, inlet flow angles and attenuation of the distortions through the compressor system. It was also capable of predicting the trends of the limiting values experienced with various orientations of the combined distortions.

Braithwaite, W. M.↗
NASA NTRS1989

The effects of temperature gradient and growth rate on the morphology and fatigue properties of MAR-M246(Hf)

MAR-M246(Hf) is a nickel based superalloy used in the turbopump blades of the Space Shuttle main engines. The effects are considered of temperature gradient (G) and growth rate (R) on the microstructure and fatigue properties of this superalloy. The primary dendrite arm spacings were found to be inversely proportional to both temperature gradient and growth rate. Carbide and gamma - gamma prime morphology trends were related to G/R ratios. Weibull analysis of fatigue results shows the characteristic life to be larger by a factor of 10 for the low gradient/fast rate pairing of G and R, while the reliability (beta) was lower.

Schmidt, D. D.↗
NASA NTRS1990

The effect of temperature cycling typical of low earth orbit satellites on thin films of YBa2Cu3O(7-x)

The refrigeration of superconductors in space poses a challenging problem. The problem could be less severe if superconducting materials would not have to be cooled when not in use. Thin films of the YBa2Cu3O(7-x) (YBCO) superconductor were subjected to thermal cycling, which was carried out to simulate a large number of eclipses of a low earth orbit satellite. Electrical measurements were performed to find the effect of the temperature cycling. Thin films of YBCO were formed by coevaporation of Y, BaF2, and Cu and postannealing in wet oxygen at 850 C for 3.5 h. The substrates used were (100) SrTiO3, polycrystalline alumina, and oxidized silicon; the last two have an evaporated zirconia layer. Processing and microstructure studies of these types of films have been published. THe zero resistance transition temperatures of the samples used in this study were 91, 82, and 86 K, respectively. The samples were characterized by four point probe electrical measurements as a function of temperature. The parameters measured were: the zero resistance transition temperature, the 10 to 90 percent transition width, and the room temperature resistance, normalized to that measured before temperature cycling. The results for two samples are presented. Each sample had a cumulative exposure. Cycling in atmospheric pressure nitrogen was performed at a rate of about 60 cycles per day, whereas in vacuum the rate was only about 10 cycles per day. The results indicate only little or no changes in the parameters measured. Degradation of superconducting thin films of YBCO has been reported due to storage in nitrogen. It is believed that the relatively good performance of films after temperature cycling is related to the fact that BaF2 was used as an evaporation source. The latest result on extended temperature cycling indicates significant degradation. Further tests of extended cycling will be carried out to provide additional data and to clarify this preliminary finding.

Mogro-Campero, A.↗
NASA NTRS1990

Photospheres of hot stars. IV - Spectral type O4

The basic stellar parameters of a supergiant (Zeta Pup) and two main-sequence stars, 9 Sgr and HD 46223, at spectral class O4 are determined using line profile analysis. The stellar parameters are determined by comparing high signal-to-noise hydrogen and helium line profiles with those from stellar atmosphere models which include the effect of radiation scattered back onto the photosphere from an overlying stellar wind, an effect referred to as wind blanketing. At spectral class O4, the inclusion of wind-blanketing in the model atmosphere reduces the effective temperature by an average of 10 percent. This shift in effective temperature is also reflected by shifts in several other stellar parameters relative to previous O4 spectral-type calibrations. It is also shown through the analysis of the two O4 V stars that scatter in spectral type calibrations is introduced by assuming that the observed line profile reflects the photospheric stellar parameters.

Bohannan, Bruce↗
NASA NTRS2016

Lucifer's Planet: Photolytic Hazes in the Atmosphere of 51 Eri b

We use a 1D model to address photochemistry and possible haze formation in the irradiated atmosphere of 51 Eri b (2016arXiv160407388Z). The intended focus was to have been on carbon and organic hazes, but sulfur photochemistry turns out to be interesting and possibly more important. The case for organic photochemical hazes is intriguing but falls short of being compelling. If organic hazes form abundantly, they are likeliest to do so if vertical mixing in 51 Eri b is weaker than in Jupiter, and they would be found below the altitudes where methane and water are photolyzed. The more novel result is that photochemistry turns H2S into elemental sulfur, here treated as S8. In the cooler models, S8 is predicted to condense in optically significant clouds of solid sulfur particles, whilst in the warmer models S8 remains a vapor along with several other sulfur allotropes that are both visually striking and potentially observable. For 51 Eri b, the division between models with and without condensed sulfur is at an effective temperature of 700 K, which is within error its actual effective temperature; the local temperature where sulfur condenses is between 280 and 320 K. The sulfur photochemistry we discuss is quite general and ought to be found in a wide variety of worlds over a broad temperature range, both colder and hotter than the 650-750 K range studied here, and we show that products of sulfur photochemistry will be nearly as abundant on planets where the UV irradiation is orders of magnitude weaker than it is on 51 Eri b.

photochemistry↗
NASA NTRS2016

Photolytic Hazes in the Atmosphere of 51 Eri b

We use a 1D model to address photochemistry and possible haze formation in the irradiated warm Jupiter 51 Eridani b. The intended focus was to be carbon, but sulfur photochemistry turns out to be important. The case for organic photochemical hazes is intriguing but falls short of being compelling. If they form, they are likeliest to do so if vertical mixing in 51 Eri b is weaker than in Jupiter, and they would be found below the regions where methane and water are photolyzed. The more novel result is that photochemistry turns H2S into elemental sulfur, here treated as S8. In the cooler models, S8 is predicted to condense in optically thick clouds of solid sulfur particles, whilst in the warmer models S8 remains a vapor along with several other sulfur allotropes that are both visually striking and potentially observable. For 51 Eri b, the division between models with and without condensed sulfur is at an effective temperature of 700 K, which is within error its actual effective temperature; the local temperature where sulfur condenses is between 280 and 320 K. The sulfur photochemistry we have discussed is quite general and ought to be found in a wide variety of worlds over a broad temperature range, both colder and hotter than the 650-750 K range studied here, and we show that products of sulfur photochemistry will be nearly as abundant on planets where the UV irradiation is orders of magnitude weaker than it is on 51 Eri b.

stars: individual(51 Eri b)↗
NASA NTRS1994

The effects of temperature and NaCl concentration on tetragonal lysozyme face growth rates

Measurements were made of the (110) and (101) face growth rates of the tetragonal form of hen egg white lysozyme at 0.1M sodium acetate buffer, pH 4.0, from 4 to 22 C and with 3.0%, 5.0%, and 7.0% NaCl used as the precipitating salt. The data were collected at supersaturation ratios ranging from approximately 4 to approximately 63. Both decreasing temperature and increasing salt concentrations shifted plots of the growth rate versus C/C(sat) to the right, i.e. higher supersaturations were required for comparable growth rates. The observed trends in the growth data are counter to those expected from the solubility data. If tetragonal lysozyme crystal growth is by addition of ordered aggregates from the solution, then the observed growth data could be explained as a result of the effects of lowered temperature and increased salt concentration on the kinetics and equilibrium processes governing protein-protein interactions in solution. The data indicate that temperature would be a more tractable means of controlling the growth rate for tetragonal lysozyme crystals contrary to the usual practice in, e.g., vapor diffusion protein crystal growth, where both the precipitant and protein concentrations are simultaneously increased. However, the available range for control is dependent upon the protein concentration, with the greatest growth rate control being at the lower concentration.

Forsythe, Elizabeth↗
NASA NTRS2003

Oxidation of ZrB2-and HfB2-Based Ultra-High Temperature Ceramics: Effects of Ta Additions

Several compositions of ZrB2- and HfB2-based Ultra-High Temperature Ceramics (UHTC) were oxidized in stagnant air at 1627 C in ten minute cycles for times up to 100 minutes. These compositions include: ZrB2 - 20v% SiC, HfB2 - 20v% SiC, ZrB2 - 20v% SiC - 20v% TaSi2, ZrB2 - 33v% SiC, HfB2 - 20v% SiC - 20v% TaSi2, and ZrB2 - 20v% SiC - 20v% TaC. The weight change due to oxidation was recorded. The ZrB2 - 20v% SiC - 20v% TaSi2 composition was also oxidized in stagnant air at 1927 C and in an arc jet atmosphere. Samples were analyzed after oxidation by x-ray diffraction, field emission scanning electron microscopy, and energy dispersive spectroscopy to determine the reaction products and to observe the microstructure. The ZrB2 - 20v% SiC - 20v% TaSi2 showed the lowest oxidation rate at 1627 C, but performed poorly under the more extreme tests due to liquid phase formation. Effects of Ta-additions on the oxidation of the diboride-based UHTC are discussed.

Opila, Elizabeth↗
NASA NTRS1994

X-ray sources in regions of star formation. 5: The low mass stars of the Upper Scorpius association

We report followup investigations of Einstein x-ray observations of the Upper Scorpius OB association. We identify 28 low mass pre-main sequence stars as counterparts of x-ray sources in the approximately = 7 square degrees of the OB association observed. Based on kinematics and lithium abundances, these stars are low mass members of the OB association. We use optical spectra and optical and near-IR photometry to determine the stellar luminosities, effective temperatures, masses, and ages. We show that the bolometric corrections and effective temperatures of the G and K stars are consistent with those of subgiants. The low mass stars have isochronal ages of 1-2 Myr, depending on the choice of evolutionary models, with very small dispersion (sigma approximately = 1 Myr). This age is significantly younger than the 5-6 Myr found for the more massive B stars. The small dispersion in stellar ages, less than 10% the sound-crossing time of the association, suggests that star formation was triggered. We present two scenarios for star formation in this association. In the two-episode scenario, formation of the low mass stars was triggered by a supernova explosion, and the low mass stars form quickly, with high efficiency. Alternatively, high and low mass star formation was all initiated at the same time, some 5-6 Myr ago, and the apparent systematic age difference is an artifact of how the isochrones are dated. The effect of the supernova is to terminate mass accretion and yield an apparently coeval population. We show that the incompleteness in the x-ray sampling is about 65%, and is strongly dependent on stellar mass. After correction for incompleteness, we estimate there are about 2000 low mass members (stellar mass less than 2 solar mass) of this association. The mass function in this association is indistinguishable from that of the field. The ratio of naked to classical T Tauri stars is much larger than in Tau-Aur, and may be attributable to the local environment. We also present observations of eight ROX sources associated with the rho Oph cloud, and observations of non-pre-main sequence (PMS) stars in our fields.

Walter, Frederick M.↗
NASA NTRS2014

The Role of Higher-Order Modes on the Electromagnetic Whistler-Cyclotron Wave Fluctuations of Thermal and Non-Thermal Plasmas

Two fundamental challenging problems of laboratory and astrophysical plasmas are the understanding of the relaxation of a collisionless plasmas with nearly isotropic velocity distribution functions and the resultant state of nearly equipartition energy density with electromagnetic plasma turbulence. Here, we present the results of a study which shows the role that higher-order-modes play in limiting the electromagnetic whistler-like fluctuations in a thermal and non-thermal plasma. Our main results show that for a thermal plasma the magnetic fluctuations are confined by regions that are bounded by the least-damped higher order modes. We further show that the zone where the whistler-cyclotron normal modes merges the electromagnetic fluctuations shifts to longer wavelengths as the beta(sub e) increases. This merging zone has been interpreted as the beginning of the region where the whistler-cyclotron waves losses their identity and become heavily damped while merging with the fluctuations. Our results further indicate that in the case of nonthermal plasmas, the higher-order modes do not confine the fluctuations due to the effective higher-temperature effects and the excess of suprathermal plasma particles. The analysis presented here considers the second-order theory of fluctuations and the dispersion relation of weakly transverse fluctuations, with wave vectors parallel to the uniform background magnetic field, in a finite temperature isotropic bi-Maxwellian and Tsallis-kappa-like magnetized electron-proton plasma. Our results indicate that the spontaneously emitted electromagnetic fluctuations are in fact enhanced over these quasi modes suggesting that such modes play an important role in the emission and absorption of electromagnetic fluctuations in thermal or quasi-thermal plasmas.

Vinas, Adolfo F.↗
NASA NTRS2007

Effect of Temperature Cycling and Exposure to Extreme Temperatures on Reliability of Solid Tantalum Capacitors

In this work, results of multiple temperature cycling (TC) (up to 1,000 cycles) of different types of solid tantalum capacitors are analyzed and reported. Deformation of chip tantalum during temperature variations simulating reflow soldering conditions was measured to evaluate the possibility of the pop-corning effect in the parts. To simulate the effect of short-time exposures to solder reflow temperatures on the reliability of tantalum capacitors, several part types were subjected to multiple cycles (up to 100) between room temperature and 240 C with periodical measurements of electrical characteristics of the parts. Mechanisms of degradation caused by temperature cycling and exposure to high temperatures, and the requirements of MIL-PRF-55365 for assessment of the resistance of the parts to soldering heat are discussed.

Teverovsky, Alexander↗
NASA NTRS2026

Thermal Considerations for 2039 Opposition Class Nuclear Electric Propulsion/Chemical Propulsion Crewed Mars Mission

The high specific impulse (Isp) of Nuclear Electric Propulsion (NEP) technology offers the potential for advanced space mission capabilities. However, the five critical technology elements of NEP vehicles have yet to prove technical maturity levels for consideration into mission design. In response to the critical reviews by the NASA Engineering and Safety Center (NESC) and the National Academies of Sciences, Engineering, and Medicine (NASEM), NASA’s Space Nuclear Propulsion (SNP) project created an NEP Technology Maturation Plan (TMP) for focused development of NEP technology. The TMP called for a coordinated set of technology development efforts to meet this objective. The Modular Assembled Radiators for NEP VehicLes (MARVL) Early Career Initiative (ECI) project was initiated to develop a portion of the fifth Critical Technology Element (CTE) of the NEP vehicle: the Primary Heat Rejection Subsystem (PHRS). A target application of a 2039 human-rated Mars mission was outlined in the TMP. For the outlined mission, a NEP vehicle will experience several thermal environments which will impact the design and operation of the PHRS. To maintain radiator temperatures within the required effective temperature range, the effect of natural, induced, and NEP internally generated heat loads on the radiator panel must be well understood. Furthermore, this analysis is critical for analyzing the influence of various orientations and positions of the NEP vehicle relative to nearby celestial bodies throughout the mission. This study conducted a complete enveloping analysis of the thermal environments influencing the NEP vehicle throughout the mission. Thermal analysis was conducted for the radiator panels based on the defined mission environments. This thermal analysis concludes with the selection of ideal radiator orientations for the NEP vehicle, and the identification of worst case hot and cold environmental sink temperatures throughout the mission. For the target application, the environmental sink temperature while the reactor is powered OFF or powered ON ranges from 30 K to 353 K and 2.7 K to 243 K respectively. When considering interplanetary space, the minimum environmental sink temperature when the reactor is powered OFF and the radiators are oriented “edge to Sun” is 2.7 K. The environmental thermal models generated in this study will be used for future studies with the full vehicle system model. The environmental sink temperature curves generated will be used for future radiator and component analysis to predict transient performance in the space environment. The environmental sink temperature and heat rejection capability curves will inform the trade between commissioning orbits that are in consideration. The model may also serve as a useful tool as reference for future crewed space missions, missions involving radiators or temperature sensitive equipment, or other missions requiring analysis of natural orbital thermal environments.

Nuclear Electric Propulsion↗
NASA NTRS1978

Effect of temperature on composite sandwich structures subjected to low velocity projectile impact

An experimental investigation was conducted to study the effect of low velocity projectile impact on graphite/epoxy and Kevlar 49- graphite/epoxy sandwich structural components. Testing was performed at moderately low- and high-temperatures to assess the strength degradation of composites as compared to room temperature values. Low energy projectile impact is considered to simulate the damage caused by runway debris such as small rocks, dropping of hand tools during servicing, etc., on secondary aircraft structures fabricated out of composites. The preload and impact energy necessary to cause catastrophic failure were determined. The residual strength of impact-damaged specimens was also measured.

Sharma, A. V.↗
NASA NTRS2017

Thermal Modeling of Mars Ground for Surface Missions

Thermal analysis packages are capable of including ground temperature effects for orbital and surface thermal analyses. In particular, Thermal Desktop® offers the option of specifying ground temperatures as a function of time for planetary surface modeling. While suitable for many cases, this approach is not sufficient if an object has local interactions with the ground that could significantly affect the ground temperature. Ground modeling is necessary for the Mars 2020 rover thermal design and analysis since shadowing and heat dissipation from the rover’s Multi-Mission Radioisotope Thermoelectric Generator (MMRTG) can result in significant temperature deviations of the local ground. The Mars 2020 thermal team is explicitly modeling the Martian ground so that these local temperature effects can be captured. The upper portion of the ground is modeled, and material and optical properties of the ground are varied in order to match data collected from orbiting science instruments. Atmospheric surface temperature, sky temperatures, and solar loads from a Mars General Circulation Model (GCM) are used as boundary conditions, resulting in a ground surface temperature profile consistent with the GCM predictions. The rover model is then placed on this modeled ground so that the effects of shadowing and MMRTG dissipation on the ground temperature can be captured.

Farias, Edgardo↗