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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 595 records · Page 33
All sourcesNASA NTRSDOE OSTI
NASA NTRS1993

Chromium and reactive element modified aluminide diffusion coatings on superalloys - Environmental testing

The high temperature performance of reactive element (RE)-doped and Cr/RE-modified aluminide diffusion coatings on commercial Ni-base alloy substrates was determined. In isothermal oxidation at 1100 C in air, RE-doped aluminide coatings on IN 713LC substrates formed a continuous slow-growing n-Al2O3 scale after 44 hrs of exposure. The coatings were protected by either an outer ridge Al2O3 scale with an inner compact Al2O3 scale rich in RE or by a continuous compact scale without any noticeable cracks or flaws. The cyclic oxidation behavior of Cr/RE-modified aluminide coatings on Rene 80 and IN 713LC alloys and of RE-doped aluminide coatings on IN 713LC alloys at 1100 C in static air was determined. Pack powder entrapment from the powder contacting (PC) process detracted significantly from the overall cyclic oxidation performance. Type I hot corrosion behavior of Cr/RE-modified aluminide coatings on Rene 80 and Mar-M247 alloy substrates at 900 C in a catalyzed 0.1 percent SO3/O3 gas mixture was determined. The modified coatings produced from the PC arrangement provided significantly better resistance to hot corrosion attack than commercial low-activity aluminide coatings produced by the above pack arrangement.

Bianco, Robert↗
NASA NTRS1992

Dependence of the cathodoluminescence of diamond films on deposition temperature

The deposition temperature dependence of the cathodoluminescence (CL) of diamond thin films grown by microwave-plasma-assisted chemical vapor deposition has been investigated. Depositions were made in the temperature range of 400 to 750 C at a pressure of 10 Torr, with a gas mixture of 5 percent CH4 and 5 percent O2 in hydrogen. The intensity of the luminescent peak at 430 nm was used as a measure of diamond quality for the film. This peak was found to be a maximum above 600 C. Examination of the intensities of CL emissions associated with nitrogen and silicon impurities at 530, 560, and 740 nm indicate incorporation of these impurities is more efficient at temperatures above 600 C. Film quality was thus found to be an optimization of competing mechanisms, i.e., improvement of diamond quality as evidenced by the intensity of the 430 nm peak, with the apparent activation of impurities and vacancy defects at elevated temperatures.

Shing, Y. H.↗
NASA NTRS1993

Convective heat-transfer rate distributions over a 140 deg blunt cone at hypersonic speeds in different gas environments

Experiments were conducted in air, CO2, and CO2-argon gas mixtures to obtain heating distribution data over a 140 deg blunt cone with various corner radii. The effect of corner radius on the heating distribution over the forebody of the cone was included in the investigation. These experiments provide data for validation of two-dimensional axisymmetric and three-dimensional Navier-Stokes solutions. Heating distribution data and measured bow shock wave stand-off distances for 0 deg angle of attack were compared with predicted values using a two-dimensional axisymmetric Navier-Stokes code.

Stewart, David A.↗
NASA NTRS1993

Models of thermal relaxation mechanics for particle simulation methods

A comparative study is conducted of the simulation of molecular vibrational relaxation in rarefied flows by means of existing models and a novel phenomenological microscopic model. This improved technique iterates between translation-rotation and rotation-vibration exchanges; equilibrium is in this way promoted if the model for the latter process is compatible with quantized oscillators. The iteration-equipartition model retains computational simplicity and promotes thermal equilibrium, even in the case of nondegenerate anharmonic quantized oscillators and multispecies gas mixtures.

Haas, Brian L.↗
NASA NTRS1993

Premixed Flame Propagation in an Optically Thick Gas

Flame propagation in both the optically thin and the optically thick regime of radiative transport was studied experimentally using particle-laden gas mixtures. Data on flame shapes, propagation rates, peak pressure, maximum rate of pressure rise, and thermal decay in the burned gases are consistent with the hypothesis that, at low particle loadings, the particles act to increase the radiative loss from the gases, whereas at higher loadings, reabsorption of emitted radiation becomes significant. The reabsorption acts to decrease the net radiative loss and augment conductive heat transport. It is speculated that, in sufficiently large systems, in which the absorption length is much smaller than the system size, flammability limits might not exist at microgravity conditions because emitted radiation would not constitute a loss mechanism.

Abbud-Madrid, Angel↗
NASA NTRS1925

Flame Speed and Spark Intensity

This report describes a series of experiments undertaken to determine whether or not the electrical characteristics of the igniting spark have any effect on the rapidity of flame spread in the explosive gas mixtures which it ignites. The results show very clearly that no such effect exists. The flame velocity in carbon-monoxide oxygen, acetylene oxygen, and gasoline-air mixtures was found to be unaffected by changes in spark intensity from sparks which were barely able to ignite the mixture up to intense condenser discharge sparks having fifty time this energy. (author)

Randolph, D W↗
NASA NTRS1993

Gas-Grain Simulation Facility (GGSF). Volume 2: Conceptual design definition

This document is Volume 2 of the Final Report for the Phase A Study of the Gas-Grain Simulation Facility (GGSF), and presents the GGSF Conceptual Design. It is a follow-on to the Volume 1 Facility Definition Study, NASA report CR 177606. The development of a conceptual design for a Space Station Freedom (SSF) facility that will be used for investigating particle interactions in varying environments, including various gas mixtures, pressures, and temperatures is delineated. It's not possible to study these experiments on earth due to the long reaction times associated with this type of phenomena, hence the need for extended periods of microgravity. The particle types will vary in composition (solids and liquids), sizes (from submicrons to centimeters), and concentrations (from single particles to 10(exp 10) per cubic centimeter). The results of the experiments pursued in the GGSF will benefit a variety of scientific inquiries. These investigations span such diverse topics as the formation of planets and planetary rings, cloud and haze processes in planetary atmospheres, the composition and structure of astrophysical objects, and the viability of airborne microbes (e.g., in a manned spacecraft).

Zamel, James M.↗
NASA NTRS1993

H2S data reduction

Calculating microwave opacity from a weakly absorbing gas mixture using a resonator requires measuring the quality factor of that resonator which necessitates accurately determining the center frequency (f(sub O)) and the half power bandwidth (Delta-f) of a noisy resonant line. The center frequency can be determined very accurately and varies very little over many measurements (a few kHz at GHz frequencies or a few hundredths of a percent). The greater source of error in estimating the Q of a resonator come from the bandwidth measurements. The half power bandwidth is determined essentially by eye-fitting a curve over a noisy resonant line and measuring with a spectrum analyzer.

Deboer, David↗
NASA NTRS1994

Nonequilibrium radiation and chemistry models for aerocapture vehicle flowfields

The primary accomplishments of the project were as follows: (1) From an overall standpoint, the primary accomplishment of this research was the development of a complete gasdynamic-radiatively coupled nonequilibrium viscous shock layer solution method for axisymmetric blunt bodies. This method can be used for rapid engineering modeling of nonequilibrium re-entry flowfields over a wide range of conditions. (2) Another significant accomplishment was the development of an air radiation model that included local thermodynamic nonequilibrium (LTNE) phenomena. (3) As part of this research, three electron-electronic energy models were developed. The first was a quasi-equilibrium electron (QEE) model which determined an effective free electron temperature and assumed that the electronic states were in equilibrium with the free electrons. The second was a quasi-equilibrium electron-electronic (QEEE) model which computed an effective electron-electronic temperature. The third model was a full electron-electronic (FEE) differential equation model which included convective, collisional, viscous, conductive, vibrational coupling, and chemical effects on electron-electronic energy. (4) Since vibration-dissociation coupling phenomena as well as vibrational thermal nonequilibrium phenomena are important in the nonequilibrium zone behind a shock front, a vibrational energy and vibration-dissociation coupling model was developed and included in the flowfield model. This model was a modified coupled vibrational dissociation vibrational (MCVDV) model and also included electron-vibrational coupling. (5) Another accomplishment of the project was the usage of the developed models to investigate radiative heating. (6) A multi-component diffusion model which properly models the multi-component nature of diffusion in complex gas mixtures such as air, was developed and incorporated into the blunt body model. (7) A model was developed to predict the magnitude and characteristics of the shock wave precursor ahead of vehicles entering the Earth's atmosphere. (8) Since considerable data exists for radiating nonequilibrium flow behind normal shock waves, a normal shock wave version of the blunt body code was developed. (9) By comparing predictions from the models and codes with available normal shock data and the flight data of Fire II, it is believed that the developed flowfield and nonequilibrium radiation models have been essentially validated for engineering applications.

Carlson, Leland A.↗
NASA NTRS1978

Synchronized flash photolysis and pulse deposition in matrix isolation experiments

An apparatus is described which permits flash photolysis of a pulse-deposited gas mixture in a matrix isolation experiment. This technique obviates the limitations of in situ photolysis imposed by the cage effect and by secondary photolysis. The matrix is deposited in pulses at 30-s intervals and photolyzed sequentially by four synchronized flashlamps approximately 1 ms before the pulse strikes the cold surface. Pulsed deposition maintains adequate isolation and causes line narrowing, which enhances spectral sensitivity. The efficacy of flash photolysis combined with pulsed deposition for producing and trapping transient species was demonstrated by infrated detection of CF3 (from photolysis of CF3I/Ar mixtures) and of ClCO (from photolysis of Cl2/CO/Ar mixtures). The apparatus was used to study the photolytic decomposition of gaseous tricarbonylironcyclobutadiene, C4H4Fe(CO)3. The results indicate that the primary photolytic step is not elimination of C4H4, as suggested earlier, but rather of CO.

Allamandola, Louis J.↗
NASA NTRS1994

Chemical investigation of Titan and Triton tholins

We report chromatographic and spectroscopic analyses of both Titan and Triton tholins, organic solids made from the plasma irradiation of 0.9:0.1 and 0.999:0.001 N2/CH4 gas mixtures, respectively. The lower CH4 mixing ratio leads to a nitrogen-richer tholin (N/C greater than 1), probably including nitrogen heterocyclic compounds. Unlike Titan tholin, bulk Triton tholin is poor in nitriles. From high-pressure liquid chromatography, ultraviolet and infrared spectroscopy, and molecular weight estimation by gel filtration chromatography, we conclude that (1) several H2O-soluble fractions, each with distinct UV and IR spectral signatures, are present, (2) these fractions are not identical in the two tholins, (3) the H2O-soluble fractions of Titan tholins do not contain significant amounts of nitriles, despite the major role of nitriles in bulk Titan tholin, and (4) the H2O-soluble fractions of both tholins are mainly molcules containing about 10 to 50 (C + N) atoms. We report yields of amino acids upon hydrolysis of Titan and Triton tholins. Titan tholin is largely insoluble in the putative hydrocarbon lakes or oceans on Titan, but can yield the H2O-soluble species investigated here upon contact with transient (e.g., impact-generated) liquid water.

Mcdonald, Gene D.↗
NASA NTRS1994

Monte Carlo prediction of radiative heat transfer in inhomogeneous, anisotropic, nongray media

A Monte Carlo solution technique has been formulated to predict the radiative heat transfer in three-dimensional, inhomogeneous participating media which exhibit spectrally dependent emission and absorption and anisotropic scattering. Details of the technique and selected numerical sensitivities are discussed. The technique was applied to a problem involving a medium composed of a gas mixture of carbon dioxide and nitrogen and suspended carbon particles. A homogeneous medium was modeled to examine the effect of total pressure and carbon-particle concentration on radiative heat transfer. Variation in total pressure, over the range studied, had minimal effect on the amount of heat radiated to the enclosure walls and on the radiative-flux distribution within the medium. Increases in the carbon particle concentration produced significantly higher heat fluxes at the boundaries and altered the radiative flux distribution. The technique was then applied to an inhomogeneous medium to examine effects of specific temperature and carbon particle concentration distributions on radiative heat transfer. For the inhomogeneous conditions examined, the largest radiative flux divergence occurs near the center of the medium and the regions near some enclosure walls act as energy sinks.

HEAT FLUXES↗
NASA NTRS1993

The effect of Na vapor on the Na content of chondrules

Chondrules contain higher concentrations of volatiles (Na) than expected for melt droplets in the solar nebula. Recent studies have proposed that chondrules may have formed under non-canonical nebular conditions such as in particle/gas-rich clumps. Such chondrule formation areas may have contained significant Na vapor. To test the hypothesis of whether a Na-rich vapor would minimize Na volatilization reaction rates in a chondrule analog and maintain the Na value of the melt, experiments were designed where a Na-rich vapor could be maintained around the sample. A starting material with a melting point lower that typical chondrules was required to keep the logistics of working with Na volatilization from NaCl within the realm of feasibility. The Knippa basalt, a MgO-rich alkali olivine basalt with a melting temperature of 1325 +/- 5 C and a Na2O content of 3.05 wt%, was used as the chondrule analog. Experiments were conducted in a 1 atm, gas-mixing furnace with the fO2 controlled by a CO/CO2 gas mixture and fixed at the I-W buffer curve. To determine the extent of Na loss from the sample, initial experiments were conducted at high temperatures (1300 C - 1350 C) for duration of up to 72 h without a Na-rich vapor present. Almost all (up to 98%) Na was volatilized in runs of 72 h. Subsequent trials were conducted at 1330 C for 16 h in the presence of a Na-rich vapor, supplied by a NaCl-filled crucible placed in the bottom of the furnace. Succeeding Knudsen cell weight-loss mass-spectrometry analysis of NaCl determined the P(sub Na) for these experimental conditions to be in the 10(exp -6) atm range. This value is considered high for nebula conditions but is still plausible for non-canonical environments. In these trials the Na2O content of the glass was maintained or in some cases increased; Na2O values ranged from 2.62% wt to 4.37% wt. The Na content of chondrules may be controlled by the Na vapor pressure in the chondrule formation region. Most heating events capable of producing chondrules are sufficient to volatile Na. Sodium volatilization reaction rates will be reduced to varying degrees from melt droplets, depending on the magnitude of the P(sub Na) generated. A combination of Na vapor during, and Na diffusion back into chondrules after, formation could maintain and/or enrich Na concentrations in chondrules.

Lewis, R. Dean↗
NASA NTRS1995

Computational Study of Flow Establishment in a Ram Accelerator

The temporal evolution of the combustion process established during projectile transition from the launch tube into the ram accelerator section containing an explosive hydrogen-oxygen-argon gas mixture is studied. The Navier-Stokes equations for chemically reacting flow are solved in a fully coupled manner, using an implicit, time accurate algorithm. The solution procedure is based on a spatially second order total variation diminishing scheme and a temporally second order, variable-step, backward differentiation formula method. The hydrogen-oxygen chemistry is modeled with a 9-species, 19-step mechanism. The accuracy of the solution method is first demonstrated by several benchmark calculations. Numerical simulations of two ram accelerator configurations are then presented. In particular, the temporal developments of shock-induced combustion and thrust forces are followed. Positive thrust is established in both cases; however, in one of the ram accelerator configurations studied, combustion in the boundary layer enhances its separation, ultimately resulting in unstart.

Yungster, S.↗
NASA NTRS1995

General Fluid System Simulation Program to Model Secondary Flows in Turbomachinery

The complexity and variety of turbomachinery flow circuits created a need for a general fluid system simulation program for test data anomaly resolution as well as design review. The objective of the paper is to present a computer program that has been developed to support Marshall Space Flight Center's turbomachinery internal flow analysis efforts. The computer program solves for the mass. energy and species conservation equation at each node and flow rate equation at each branch of the network by a novel numerical procedure which is a combination of both Newton-Ralphson and successive substitution method and uses a thermodynamic property program for computing real gas properties. A generalized, robust, modular, and 'user-friendly' computer program has been developed to model internal flow rates, pressures, temperatures, concentrations of gas mixtures and axial thrusts. The program can be used for any network for compressible and incompressible flows, choked flow, change of phase and gaseous mixturecs. The code has been validated by comparing the predictions with Space Shuttle Main Engine test data.

Majumdar, Alok K.↗
NASA NTRS1996

NEQAIR96,Nonequilibrium and Equilibrium Radiative Transport and Spectra Program: User's Manual

This document is the User's Manual for a new version of the NEQAIR computer program, NEQAIR96. The program is a line-by-line and a line-of-sight code. It calculates the emission and absorption spectra for atomic and diatomic molecules and the transport of radiation through a nonuniform gas mixture to a surface. The program has been rewritten to make it easy to use, run faster, and include many run-time options that tailor a calculation to the user's requirements. The accuracy and capability have also been improved by including the rotational Hamiltonian matrix formalism for calculating rotational energy levels and Hoenl-London factors for dipole and spin-allowed singlet, doublet, triplet, and quartet transitions. Three sample cases are also included to help the user become familiar with the steps taken to produce a spectrum. A new user interface is included that uses check location, to select run-time options and to enter selected run data, making NEQAIR96 easier to use than the older versions of the code. The ease of its use and the speed of its algorithms make NEQAIR96 a valuable educational code as well as a practical spectroscopic prediction and diagnostic code.

Whiting, Ellis E.↗
NASA NTRS1997

Paralinear Oxidation of CVD SiC in Water Vapor

The oxidation kinetics of CVD SiC were monitored by thermogravimetric analysis (TGA) in a 50% H2O/50% O2 gas mixture flowing at 4.4 cm/s for temperatures between 1200 and 1400 C. Paralinear weight change kinetics were observed as the water vapor oxidized the SiC and simultaneously volatilized the silica scale. The long-term degradation rate of SiC is determined by the volatility of the silica scale. Rapid SiC surface recession rates were estimated from these data for actual aircraft engine combustor conditions.

Opila, Elizabeth J.↗
NASA NTRS1997

Mining the Mars Atmosphere

A series of concepts have been developed to mine the atmosphere of Mars and process it to extract or generate compressed carbon dioxide, compressed buffer gas mixtures of nitrogen and argon, water, oxygen, carbon monoxide, and/or carbon. Such products can be of use to science instruments, robotic, and human missions. The products can be for utility purposes, life support, propulsion (both interplanetary and on the planet's surface), and power generation.

Finn, John E.↗