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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 235 records · Page 13
All sourcesNASA NTRSDOE OSTI
NASA NTRS1974

A statistical-chemical and thermodynamic approach to the study of lunar mineralogy

Principal components analysis is used to study the chemical compositions of pyroxenes of five Apollo 12 specimens. Important correlations are recognized in the variation of oxide weight per cent. These correlations indicating substitutional relationships can be interpreted as representative of stable and metastable trends of crystallization by using crystal-chemical and thermodynamic information. The per cent variance of pyroxene groups with characteristic trends in each specimen can be evaluated and interpreted in terms of history of crystallization. Distribution of Fe and Mg in certain pairs of olivine and pyroxene, which are found in contact in the rock and which may have crystallized simultaneously, is useful in recognizing the tendency towards chemical equilibrium in Fe-Mg distribution during a limited interval in the liquidus or subsolidus stages.

Saxena, S. K.↗
NASA NTRS1974

Exospheric temperature and composition from satellite beacon measurements

Routine measurements of the slab thickness of the ionosphere, from 1965 to 1971, are used to infer the changes in neutral temperature and ion composition at a mean latitude of 40 S. Values of neutral temperature at solar maximum are 5 to 10% above Northern Hemisphere backscatter results. The diurnal and seasonal changes agree closely with satellite drag and backscatter measurements, except that the maximum temperature occurs after sunset in winter. Winter night-time values of the O(+)/H(+) transition height were 500 km in 1965-1966, 800 km in 1968-1969, and 700 km in 1971. Changes in the transition height lag about six months behind the changes in solar flux. Diurnal variations have a minimum just before sunrise and a maximum 1 to 3 hr after noon. On winter nights the transition height descends to the level set by chemical equilibrium. On summer nights the transition height is always above this level, giving a continual production of H(+) which serves as an additional source for maintaining the night-time ionosphere in the winter hemisphere.

Titheridge, J. E.↗
NASA NTRS1974

Hydrogen ionization in the shock layer for entry into the outer planets

Approximate assessments are presented for the chemical state of the shock layer with respect to the hydrogen ionization reaction for representative entries into Saturn, Uranus, and Jupiter. It is shown that, except for a steep entry into the Saturn nominal atmosphere, the computation of all entry probe gascaps for the outer planets can probably be considered on either a frozen or chemical equilibrium basis.

Howe, J. T.↗
NASA NTRS1974

Chemical fractionation in the solar nebula

The sequence of condensation of minerals from a cooling gas of solar composition has been calculated from thermodynamic data assuming complete chemical equilibrium is maintained. The results suggest that the Ca-Al-rich inclusions in Allende and other carbonaceous chondrites are aggregates of the highest temperature condensates. Complete condensation of these elements is followed 100 deg later, by the onset of the crystallization of nickel-iron, forsterite and enstatite. Transport of Ca-Al-rich refractory condensates from one part of the nebula to another before the condensation of these lower-temperature phases may have been responsible for the refractory element fractionations between the different classes of chondrites and possibly for the inferred refractory element enrichment of the moon.

Grossman, L.↗
NASA NTRS1975

Hypersonic research engine project. Phase 2: Aerothermodynamic Integration Model (AIM) data reduction computer program, data item no. 54.16

The data reduction program used to analyze the performance of the Aerothermodynamic Integration Model is described. Routines to acquire, calibrate, and interpolate the test data, to calculate the axial components of the pressure area integrals and the skin function coefficients, and to report the raw data in engineering units are included along with routines to calculate flow conditions in the wind tunnel, inlet, combustor, and nozzle, and the overall engine performance. Various subroutines were modified and used to obtain species concentrations and transport properties in chemical equilibrium at each of the internal and external engine stations. It is recommended that future test plans include the configuration, calibration, and channel assignment data on a magnetic tape generated at the test site immediately before or after a test, and that the data reduction program be designed to operate in a batch environment.

Gaede, A. E.↗
NASA NTRS1975

Numerical methods for the calculation of three-dimensional nozzle exhaust flow fields

Numerical codes developed for the calculation of three-dimensional nozzle exhaust flow fields associated with hypersonic airbreathing aircraft are described. Both codes employ reference plane grid networks with respect to three coordinate systems. Program CHAR3D is a characteristic code utilizing a new wave preserving network within the reference planes, while program BIGMAC is a finite difference code utilizing conservation variables and a one-sided difference algorithm. Secondary waves are numerically captured by both codes, while the underexpansion shock and plume boundary are treated discretely. The exhaust gas properties consist of hydrogen-air combustion product mixtures in local chemical equilibrium. Nozzle contours are treated by a newly developed geometry package based on dual cubic splines. Results are presented for simple configurations demonstrating two- and three-dimensional multiple wave interactions.

Dash, S. M.↗
NASA NTRS1975

Chemically Reacting One-Dimensional Gas-Particle Flows

The governing equations for the one-dimensional flow of a gas-particle system are discussed. Gas-particle effects are coupled via the system momentum and energy equations with the gas assumed to be chemically frozen or in chemical equilibrium. A computer code for calculating the one-dimensional flow of a gas-particle system is discussed and a user's input guide presented. The computer code provides for the expansion of the gas-particle system from a specified starting velocity and nozzle inlet geometry. Though general in nature, the final output of the code is a startline for initiating the solution of a supersonic gas-particle system in rocket nozzles. The startline includes gasdynamic data defining gaseous startline points from the nozzle centerline to the nozzle wall and particle properties at points along the gaseous startline.

Tevepaugh, J. A.↗
NASA NTRS1976

Turbulent viscous-shock-layer solutions with strong vorticity interaction

Numerical solutions of the viscous-shock-layer equations governing laminar and turbulent flows of a perfect gas and radiating and nonradiating mixtures of perfect gases in chemical equilibrium are presented for hypersonic flow over spherically blunted cones and hyperboloids. The results are compared with boundary-layer and inviscid flow-field solutions. The agreement with the inviscid flow field data is satisfactory. The agreement with boundary-layer solutions is good except in regions of strong vorticity interaction. In these flow regions, the viscous-shock-layer solutions appear to be more satisfactory than the boundary-layer solutions.

Anderson, E. C.↗
NASA NTRS1976

Molecular hydrogen in interstellar dark clouds

A simplified H2 formation mechanism is proposed in which small interstellar grains furnish the reaction sites. This mechanism results in a maximum value for the rate constant of about 2 by 10 to the -18th power per cu cm/sec for dark clouds at 10 K. Also, the nascent molecules are ejected in excited states, in qualitative agreement with Copernicus observations. A time-dependent treatment of the chemical evolution of a dark cloud with little or no ionizing radiation shows that the clouds require more than 10 million years to achieve chemical equilibrium. The observed residual atomic hydrogen in several dark clouds suggests that the clouds are 1 to 10 million years old. Other consequences of the temporal cloud model are in accord with astronomical observations.

Allen, M.↗
NASA NTRS1977

Vorticity interaction effects on blunt bodies

Numerical solutions of the viscous shock layer equations governing laminar and turbulent flows of a perfect gas and radiating and nonradiating mixtures of perfect gases in chemical equilibrium are presented for hypersonic flow over spherically blunted cones and hyperboloids. Turbulent properties are described in terms of the classical mixing length. Results are compared with boundary layer and inviscid flowfield solutions; agreement with inviscid flowfield data is satisfactory. Agreement with boundary layer solutions is good except in regions of strong vorticity interaction; in these flow regions, the viscous shock layer solutions appear to be more satisfactory than the boundary layer solutions. Boundary conditions suitable for hypersonic viscous shock layers are devised for an advanced turbulence theory.

Anderson, E. C.↗
NASA NTRS1977

Combustion of hydrogen injected into a supersonic airstream (the SHIP computer program)

The mathematical and physical basis of the SHIP computer program which embodies a finite-difference, implicit numerical procedure for the computation of hydrogen injected into a supersonic airstream at an angle ranging from normal to parallel to the airstream main flow direction is described. The physical hypotheses built into the program include: a two-equation turbulence model, and a chemical equilibrium model for the hydrogen-oxygen reaction. Typical results for equilibrium combustion are presented and exhibit qualitatively plausible behavior. The computer time required for a given case is approximately 1 minute on a CDC 7600 machine. A discussion of the assumption of parabolic flow in the injection region is given which suggests that improvement in calculation in this region could be obtained by use of the partially parabolic procedure of Pratap and Spalding. It is concluded that the technique described herein provides the basis for an efficient and reliable means for predicting the effects of hydrogen injection into supersonic airstreams and of its subsequent combustion.

Markatos, N. C.↗
NASA NTRS1977

Nozzle flow of laser-heated radiating hydrogen with application to a laser-heated rocket

This paper presents a model for the steady heating of flowing hydrogen by a CW 10.6 micron laser, to consider the feasibility of a laser-heated rocket. The hydrogen flow and the laser beam are parallel, and move into a converging-diverging nozzle. The absorption of laser energy is initiated by a laser-supported combustion wave. The hydrogen is in chemical equilibrium, absorbs laser energy by inverse Bremsstrahlung, and loses energy by radiation. The hydrogen flow was calculated from the rear of the LSC wave to the throat. Estimates of convective heat losses were made using a hydrogen boundary layer analysis. Specific impulse, obtained by expanding isentropically from the throat to 1 atm or a vacuum, varies from 1400 to 3000 s. Radiation losses are 5 to 20%, though the energy fluxes to the walls are quite high. Convective loss estimates are high enough to indicate that coupling to the hot gas flow is required for a 10 kW engine, but not for a 5 MW engine.

Kemp, N. H.↗
NASA NTRS1977

Chemical fractionation in the solar nebula

The sequence of condensation of minerals from a cooling gas of solar composition has been calculated from thermodynamic data over the pressure range 0.001-0.00001 atm, assuming that complete chemical equilibrium is maintained. The results suggest that the Ca-Al-rich inclusions Allende and other carbonaceous chondrites are aggregates of the highest temperature condensates. Complete condensation of these elements is followed, 100 deg later, by the onset of the crystallization of nickel-iron, forsterite and enstatite. Transport of Ca-Al-rich refractory condensates from one part of the nebula to another before the condensation of these lower-temperature phases may have been responsible for the refractory element fractionations between the different classes of chondrites and possibly for the inferred refractory element enrichment of the Moon. The temperature gap between the condensation temperatures of nickel-iron and forsterite increases with increasing total pressure. Because pressure and temperature probably increased with decreasing heliocentric distance in the solar nebula, Mercury may have accreted from a condensate assemblage having a higher metal/silicate ratio than Venus or Earth which may, in turn, have formed from less oxidized material than Mars.

Grossman, L.↗
NASA NTRS1976

Gas core reactors for coal gasification

The concept of using a gas core reactor to produce hydrogen directly from coal and water is presented. It is shown that the chemical equilibrium of the process is strongly in favor of the production of H2 and CO in the reactor cavity, indicating a 98% conversion of water and coal at only 1500 K. At lower temperatures in the moderator-reflector cooling channels the equilibrium strongly favors the conversion of CO and additional H2O to CO2 and H2. Furthermore, it is shown the H2 obtained per pound of carbon has 23% greater heating value than the carbon so that some nuclear energy is also fixed. Finally, a gas core reactor plant floating in the ocean is conceptualized which produces H2, fresh water and sea salts from coal.

Weinstein, H.↗
NASA NTRS1978

Experimental study of the effect of cycle pressure on lean combustion emissions

Experiments were conducted in which a stream of premixed propane and air was burned under conditions representative of gas turbine operation. Emissions of NOx, CO, and unburned hydrocarbons (UHC) were measured over a range of combustor inlet temperature, pressure, and residence time at equivalence ratios from 0.7 down to the lean stability limit. At an inlet temperature of 600 K, observed NOx levels dropped markedly with decreasing pressure for pressures below 20 atm. The NOx levels are proportional to combustor residence time and formation rates were principally a function of adiabatic flame temperature. For adiabatic flame temperatures of 2050 K and higher, CO reached chemical equilibrium within 2 msec. Unburned hydrocarbon species dropped to a negligible level within 2 msec regardless of inlet temperature, pressure, or equivalence ratio. For a combustor residence time of 2.5 msec, combustion inefficiency became less than 0.01% at an adiabatic flame temperature of 2050 K. The maximum combustion inefficiency observed was on the order of 1% and corresponded to conditions near the lean stability limit. Using a perforated plate flameholder, this limit is well represented by the condition of 1800 K adiabatic flame temperature.

Roffe, G.↗
NASA NTRS1977

Computational models for the analysis of three-dimensional internal and exhaust plume flowfields

This paper describes computational procedures developed for the analysis of three-dimensional supersonic ducted flows and multinozzle exhaust plume flowfields. The models/codes embodying these procedures cater to a broad spectrum of geometric situations via the use of multiple reference plane grid networks in several coordinate systems. Shock capturing techniques are employed to trace the propagation and interaction of multiple shock surfaces while the plume interface, separating the exhaust and external flows, and the plume external shock are discretely analyzed. The computational grid within the reference planes follows the trace of streamlines to facilitate the incorporation of finite-rate chemistry and viscous computational capabilities. Exhaust gas properties consist of combustion products in chemical equilibrium. The computational accuracy of the models/codes is assessed via comparisons with exact solutions, results of other codes and experimental data. Results are presented for the flows in two-dimensional convergent and divergent ducts, expansive and compressive corner flows, flow in a rectangular nozzle and the plume flowfields for exhausts issuing out of single and multiple rectangular nozzles.

Dash, S. M.↗
NASA NTRS1977

The chemical evolution of molecular clouds

The nonequilibrium chemistry of dense molecular clouds (10,000 to 1 million hydrogen molecules per cu cm) is studied in the framework of a model that includes the latest published chemical data and most of the recent theoretical advances. In this model the only important external source of ionization is assumed to be high-energy cosmic-ray bombardment; standard charge-transfer reactions are taken into account as well as reactions that transfer charge from molecular ions to trace-metal atoms. Schemes are proposed for the synthesis of such species as NCO, HNCO, and CN. The role played by adsorption and condensation of molecules on the surface of dust grains is investigated, and effects on the chemical evolution of a dense molecular cloud are considered which result from varying the total density or the elemental abundances and from assuming negligible or severe condensation of gaseous species on dust grains. It is shown that the chemical-equilibrium time scale is given approximately by the depletion times of oxygen and nitrogen when the condensation efficiency is negligible; that this time scale is probably in the range from 1 to 4 million years, depending on the elemental composition and initial conditions in the cloud; and that this time scale is insensitive to variations in the total density.

Iglesias, E.↗
NASA NTRS1978

Turbulent viscous shock layer solutions for Jovian entry at small angles of attack

The equations governing the laminar and turbulent flows of reacting gas mixtures in chemical equilibrium over axially symmetric blunt bodies at small angles of attack are developed and presented in the unsteady conservative form. Solutions are obtained in the planes of symmetry of the flow field for the typical conditions encountered by a probe entering the Jovian atmosphere at small angles of attack. The eddy-viscosity is approximated by a two-layer model. The shock wave is treated as a discontinuity across which the shock relations are used to compute the flow conditions behind the shock. A time-asymptotic finite-difference method is used to solve the equations. The zero angle of attack results for a hyperboloid are compared with the existing results but neither experimental nor computational results are available for comparison with the present results at angle of attack.

Jumar, A.↗