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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 37 records · Page 2
All sourcesNASA NTRSDOE OSTI
NASA NTRS1992

Chemical differentiation of a convecting planetary interior: Consequences for a one-plate planet such as Venus

Chemically depleted mantle forming a buoyant, refractory layer at the top of the mantle can have important implications for the evolution of the interior and surface. On Venus, the large apparent depths of compensation for surface topographic features might be explained if surface topography were supported by variations in the thickness of a 100-200 km thick chemically buoyant mantle layer or by partial melting in the mantle at the base of such a layer. Long volcanic flows seen on the surface may be explained by deep melting that generates low-viscosity MgO-rich magmas. The presence of a shallow refractory mantle layer may also explain the lack of volcanism associated with rifting. As the depleted layer thickens and cools, it becomes denser than the convecting interior and the portion of it that is hot enough to flow can mix with the convecting mantle. Time dependence of the thickness of a depleted layer may create episodic resurfacing events as needed to explain the observed distribution of impact craters on the venusian surface. We consider a planetary structure consisting of a crust, depleted mantle layer, and a thermally and chemically well-mixed convecting mantle. The thermal evolution of the convecting spherical planetary interior is calculated using energy conservation: the time rate of change of thermal energy in the interior is equated to the difference in the rate of radioactive heat production and the rate of heat transfer across the thermal boundary layer. Heat transfer across the thermal boundary layer is parameterized using a standard Nusselt number-Rayleigh number relationship. The radioactive heat production decreases with time corresponding to decay times for the U, Th, and K. The planetary interior cools by the advection of hot mantle at temperature T interior into the thermal boundary layer where it cools conductively. The crust and depleted mantle layers do not convect in our model so that a linear conductive equilibrium temperature distribution is assumed. The rate of melt production is calculated as the product of the volume flux of mantle into the thermal boundary layer and the degree of melting that this mantle undergoes. The volume flux of mantle into the thermal boundary layer is simply the heat flux divided by amount of heat lost in cooling mantle to the average temperature in the thermal boundary layer. The degree of melting is calculated as the temperature difference above the solidus, divided by the latent heat of melting. A maximum degree of melting is prescribed corresponding to the maximum amount of basaltic melt that the mantle can initially generate. As the crust thickens, the pressure at the base of the crust becomes high enough and the temperature remains low enough for basalt to transform to dense eclogite.

Parmentier, E. M.↗
NASA NTRS1972

The diurnal heat budget of the thermosphere

Detailed numerical calculations of thermospheric heat sources and sinks are presented and their relative importance is discussed in reference to the energy balance phenomena of the neutral atmosphere. It is shown that the thermal energy available from the absorption in the Schumann-Runge continuum leading to photodissociation of O2 is by far the largest energy source in the lower thermosphere. Other sources of varying importance in different altitude ranges are: (1) energy from photoelectrons, (2) energy exchange from thermal plasma, (3) chemical reactions (ion-electron dissociative recombination) energy gain, and (4) kinetic and dissipative energy associated with the neutral wind. The energy sinks of importance are thermal conduction at the lower boundary (120 km) and radiative cooling of atomic oxygen. It is shown that the combined energy from processes 2 to 4 constitute only a small fraction of the total energy available from photoelectrons and are in phase with the latter. It is suggested that a choice of a lower boundary much below 120 km, e.g. near the mesopause level (90 km), should be more appropriate for general thermospheric studies.

Chandra, S.↗
NASA NTRS1973

The diurnal heat budget of the thermosphere.

Detailed numerical calculations of thermospheric heat sources and sinks are presented and their relative importance is discussed in reference to the energy balance phenomena of the neutral atmosphere. It is shown that the thermal energy available from the absorption in the Schumann-Runge continuum leading to photo-dissociation of O2 is by far the largest energy source in the lower thermosphere. Other sources of varying importance in different altitude ranges are: (1) energy from photoelectrons; (2) energy exchange from thermal plasma; (3) chemical reaction (ion-electron dissociative recombination) energy gain; (4) kinetic and dissipative energy associated with the neutral wind. The energy sinks of importance are (1) thermal conduction at the lower boundary (120 km); and (2) radiative cooling of atomic oxygen. It is shown that the combined energy from processes 2 to 4 constitutes only a small fraction of the total energy available from photoelectrons and is in phase with the latter. These secondary sources (processes 2 to 4), therefore, do not constitute a significant energy source and their contribution can be simply incorporated into photoelectron energy (process 1) by defining an effective photoionization heating efficiency.

Chandra, S.↗
NASA NTRS1975

Solution of the equation of heat conduction with time dependent sources: Programmed application to planetary thermal history

A computer program (Program SPHERE) solving the inhomogeneous equation of heat conduction with radiation boundary condition on a thermally homogeneous sphere is described. The source terms are taken to be exponential functions of the time. Thermal properties are independent of temperature. The solutions are appropriate to studying certain classes of planetary thermal history. Special application to the moon is discussed.

Conel, J. E.↗
NASA NTRS1988

Transfinite element methodology for nonlinear/linear transient thermal modelling/analysis - Progress and recent advances

The 'transfinite element method' (TFEM) proposed by Tamma and Railkar (1987 and 1988) for the analysis of linear and nonlinear heat-transfer problems is described and demonstrated. The TFEM combines classical Galerkin and transform approaches with state-of-the-art FEMs to obtain a flexible hybrid modeling scheme. The fundamental principles of the TFEM and the derivation of the governing equations are reviewed, and numerical results for sample problems are presented in extensive graphs and briefly characterized. Problems analyzed include a square plate with a hole, a rectangular plate with natural and essential boundary conditions and varying thermal conductivity, the Space Shuttle thermal protection system, a bimaterial plate subjected to step temperature variations, and solidification in a semiinfinite liquid slab.

Tamma, Kumar K.↗
NASA NTRS1959

Theoretical and Experimental Investigation of Heat Conduction in Air, Including Effects of Oxygen Dissociation

Solutions are presented for the conduction of beat through a semi-infinite gas medium having a uniform initial temperature and a constant boundary temperature. The coefficients of thermal conductivity and diffusivity are treated as variables, and the solutions are extended to the case of air at temperatures where oxygen dissociation occurs. These solutions are used together with shock-tube measurements to evaluate the integral of thermal conductivity for air as a function of temperature.

Hansen, C. Frederick↗
NASA NTRS1994

Thermal analysis of a functionally graded material subject to a thermal gradient using the boundary element method

The boundary element method is utilized in this study to conduct thermal analysis of functionally graded composites, materials in which the internal microstructure or properties are explicitly tailored in order to obtain an optimal response, on the micromechanical (constituent) scale. A unique feature of the boundary element formulations used here is the use of circular shape functions to convert the two-dimensional integrations of the composite fibers to one dimensional integrations. Using the computer code BEST-CMS, the through the thickness temperature profiles are computed for a representative material with varying numbers of fibers and fiber spacing in the thickness direction. The computed temperature profiles are compared to those obtained using an alternate analytical theory which explicitly couples the heterogeneous microstructure to the global analysis. The boundary element results compared favorably to the analytical calculations, with discrepancies that are explainable based on the boundary element formulation. The results serve both to demonstrate the ability of the boundary element method to analyze these types of materials, and to verify the accuracy of the analytical theory.

Goldberg, Robert K.↗
NASA NTRS1993

Composite micromechanical modeling using the boundary element method

The use of the boundary element method for analyzing composite micromechanical behavior is demonstrated. Stress-strain, heat conduction, and thermal expansion analyses are conducted using the boundary element computer code BEST-CMS, and the results obtained are compared to experimental observations, analytical calculations, and finite element analyses. For each of the analysis types, the boundary element results agree reasonably well with the results from the other methodologies, with explainable discrepancies. Overall, the boundary element method shows promise in providing an alternative method to analyze composite micromechanical behavior.

Goldberg, Robert K.↗
NASA NTRS1993

Does the thermal wind exist near the Earth's core boundary?

Temperature distribution in the Earth core determines many important processes such as the following: convective motion, magnetic field generation, matter exchange between the core and the mantle, and the thermal flux. This distribution depends on conditions in the core-mantle boundary and on the distribution of the thermal conductivity in the mantle. Seismic tomography shows that large horizontal temperature and compositional gradients exists at the core-mantle boundary. The simple assumption that these inhomogeneities are extended into the top of the core contradicts the common opinion that the horizontal temperature gradient (the thermal wind) wipes them out in a short time. However, this conclusion has been obtained without taking into account that the core volume is closed and the motion, if it is started, can lead to a small redistribution of composition that stops this motion.

Dolginov, A. Z.↗
NASA NTRS1977

Viking Mars hydrazine terminal descent engine thermal design considerations

A description is given of some of the more significant thermal design considerations employed in the development and qualification of the monopropellant hydrazine terminal descent engines on the Viking Mars lander spacecraft. The terminal descent engine operates in a blowdown and throttling mode, which results in an operating thrust range of 638 to 90 lbf. Martian entry thermal design boundary conditions are described, along with resulting radiative and conductive engine thermal isolation hardware. Test results are presented, showing engine thermal design performance as compared with specified requirements. General engine materials of construction are described, along with Hastelloy B shell structural characteristics, which were extended to 2000 F by test and are compared with limited existing MIL-HDBK-5 data. Subscale test results are presented, showing the maximum catalyst bed cylinder design temperature of 1970 F. Test results also are presented, showing local reactor internal convective heat-transfer coefficients. Such data are unique, since the engine employs a completely radial flow catalyst bed design. This design approach is the first of its kind in the monopropellant hydrazine gas generator field to be flight qualified.

Cunningham, C. R.↗
NASA NTRSDate not supplied

Process Modeling of Woven Textiles

Woven polymer matrix composites offer numerous advantages over traditional unidirectional laminates. Processing conditions affect residual stress that builds up during manufacturing. This work proposes the analysis of three curing parameters on the local residual stress distribution of a plain weave textile architecture, including chemical shrinkage, the temperature cool down, and the evolution of matrix properties as a function of curing. Virtual curing is applied to the inter-tow matrix material of the plain weave Repeating Unit Cell (RUC) modeled in TexGen. Curing is implemented through user-written subroutines within the commercial software suite Abaqus. Results from process modeling are compared with a linear-elastic thermal cool down in Abaqus. A boundary conditions study is also conducted to compare the residual stress build up predicted by Flat(FBCs) and Periodic Boundary Conditions (PBCs). Preliminary results indicate that a thermal cool down over-estimates the end-of-cure stresses in the matrix. Process modeling is conducted with and without chemical shrinkage, then compared with a thermal cool down. Results show that 11.32% of the final stress state is due to chemical shrinkage. Material property evolution during curing also has a non-negligible effect on the end stress.

woven composites↗
NASA NTRS1974

Using the NASTRAN Thermal Analyzer to simulate a flight scientific instrument package

The NASTRAN Thermal Analyzer has proven to be a unique and useful tool for thermal analyses involving large and complex structures where small, thermally induced deformations are critical. Among its major advantages are direct grid point-to-grid point compatibility with large structural models; plots of the model that may be generated for both conduction and boundary elements; versatility of applying transient thermal loads especially to repeat orbital cycles; on-line printer plotting of temperatures and rate of temperature changes as a function of time; and direct matrix input to solve linear differential equations on-line. These features provide a flexibility far beyond that available in most finite-difference thermal analysis computer programs.

Lee, H.-P.↗
NASA NTRS1990

The effect of coatings and liners on heat transfer in a dry shaft-bush tribosystem

The temperatures due to frictional heating within a solid lubricated or coated journal bearing were analyzed by using a finite element method. A solid model of the shaft-bush tribocontact was generated with an eight-node, three-dimensional, first-order isoparametric heat-transfer element and the Patran solid modeler software. The Patmar (Patran-Marc) translator was used to help develop the Marc-based finite element program for the system; this software was used on the Cray X-MP supercomputer to perform a finite element analysis of the contact. The analysis was performed for various liner materials, for thin, hard, wear-resistant coated bearings, and for different geometries and thermal cooling boundary conditions. The analyses indicated that thermal conductivity of the liner or coating material is the most vital thermal parameter that controls the interface temperature. In addition to design variations, the proximity of the cooling source to the heat-flux-generating interface is critically important to the temperature control in the system.

Ghosh, Mihir K.↗
NASA NTRS1973

Atmospheric Aerosol and Thermal Structure in the Boundary Layer Over the Los Angeles Basin

A field study using a mobile lidar was recently conducted in the L. A. Basin, California, to (1) examine the relationship between the vertical aerosol and the thermal structure, and (2) map the vertical aerosol structure in the atmospheric boundary layer over the basin. These data are needed for use in the development of a mixing-depth submodel required for photochemical air Quality simulation models. Toward these ends, a series of lidar aerosol measurements in conjunction with balloon and aircraft temperature soundings were taken at a site in El Monte, and in a mobile mode along a 90-mile freeway loop between El Monte, Santa Monica, and Long Beach. The lidar data are presented in the form of time-height and distance-height cross sections. The results indicate that, although aerosol concentrations are frequently present above the base of the marine inversion, these are generally in stratified layers in contrast to the more uniform nature of the lower convective layer, permitting the mixing depth to be distinguished on this basis. The lidar-derived mixing depths are well correlated (within 100 m) with daytime temperature inversions. Other significant features shown by the lidar data include large Basin-wide mixing-depth variations, waves with amplitudes of 200-300 m and wavelengths of 1000-1500 m on the lower aerosol layer, and apparent aerosol "chimneys" with overrunning in the vicinity of convergence zones.

Johnson, Warren B.↗
NASA NTRS1991

Prediction of thermal acoustic oscillations (TAOs) in the CLAES solid CO2/neon system

Results are presented of a study initiated to investigate the possibility that the existence of thermal acoustic oscillations (TAOs) in the Cryogenic Limb Atmospheric Etalon Spectrometer (CLAES) neon plumbing system ground configuration could be the cause of higher-than-predicted heat rates measured during thermal ground testing. Tests were conducted between warm boundary temperatures ranging from 40 to 100 K, which simulated the actual test conditions of the CLAES CO2/neon system. TAOs were observed between 6 and 106 Torr, which agreed with the analytical predictions, and verified the possible existence of TAOs in the CLAES system during ground testing. The presence of TAOs was eventually confirmed in the CLAES system during a subsequent thermal test and were determined to have caused the higher heat rates measured during the prior thermal test.

Spradley, I. E.↗
NASA NTRS1974

Basic performance of a multilayer insulation system containing 20 to 160 layers

An experimental investigation was conducted to determine the thermal effectiveness of an aluminized Mylar-silk net insulation system containing up to 160 layers. The experimentally measured heat flux was compared with results predicted by using (1) a previously developed semi-empirical equation and (2) an effective-thermal-conductivity value. All tests were conducted at a nominal hot-boundary temperature of 294 K (530 R) with liquid hydrogen as the heat sink. The experimental results show that the insulation performed as expected and that both the semi-empirical equation and effective thermal conductivity of a small number of layers were adequate in predicting the thermal performance of a large number of layers of insulation.

Stochl, R. J.↗
NASA NTRS1991

A numerical simulation of magnetic reconnection and radiative cooling in line-tied current sheets

Radiative MHD equations are used for an optically thin plasma to carry out a numerical experiment related to the formation of 'postflare' loops. The numerical experiment starts with a current sheet that is in mechanical and thermal equilibrium but is unstable to both tearing-mode and thermal-condensation instabilities. The current sheet is line-tied at one end to a photospheric-like boundary and evolves asymmetrically. The effects of thermal conduction, resistivity variation, and gravity are ignored. In general, reconnection in the nonlinear stage of the tearing-mode instability can strongly affect the onset of condensations unless the radiative-cooling time scale is much smaller than the tearing-mode time scale. When the ambient plasma is less than 0.2, the reconnection enters a regime where the outflow from the reconnection region is supermagnetosonic with respect to the fast-mode wave speed. In the supermagnetosonic regime the most rapidly condensing regions occur downstream of a fast-mode shock that forms where the outflow impinges on closed loops attached to the photospheric-like boundary. A similar shock-induced condensation might occur during the formation of 'postflare' loops.

Forbes, T. G.↗