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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 NTRS1980

Hot hydrogen in the exosphere of Venus

Lyman-alpha measurements of the hydrogen corona of Venus by Mariners 5 and 10 have been shown to be consistent with a two-temperature component model. Bertaux et al. (1978) have successfully fitted the Venera 9 exospheric Lyman-alpha data to an elevated (500 K) single temperature. Various source mechanisms have been proposed to explain the 'hot' (1000 K) energetic component of the hydrogen corona. In the present paper recent results from the Pioneer Venus Orbiter are used to establish the major sources of this hot hydrogen population.

Cravens, T. E.↗
DOE OSTI2020

Supported Molybdenum Carbide Nanoparticles as Hot Hydrogen Reservoirs for Catalytic Applications

Transition metal carbides have been long proposed as replacements for expensive Pt-group transition metals as heterogeneous catalysts for hydrogenation reactions, featuring similar to superior activities and selectivities. Combining experimental observations and theoretical calculations, we show that the hydrogenating capabilities of molybdenum carbide can be further improved by nanostructuring, as seen on MoC y nanoclusters anchored on an inert Au(111) support, revealing a more prominent role of Mo active sites in the easier H 2 adsorption, dissociation, H adatom diffusion, and elongated chemisorbed H 2 Kubas moieties formation when compared to the bulk δ-MoC(001) surface, thus explaining the observed stronger H 2 interaction and the larger formation of CH x species, making these systems ideal to catalyse hydrogenation reactions

36 MATERIALS SCIENCE↗
NASA NTRS1993

Hot Hydrogen Testing of Refractory Metals and Ceramics

The objective of this investigation is to develop a technique with which refractory metal carbide samples can be exposed to hydrogen containing gases at high temperatures, and to use various microstructural and analytical techniques to determine the chemical and rate processes involved in hydrogen degradation in these materials. Five types of carbides were examined including WC, NbC, HfC, ZrC, and TaC. The ceramics were purchased and were all monolithic in nature. The temperature range investigated was from 850 to 1600 C with a hydrogen pressure of one atmosphere. Control experiments, in vacuum, were also conducted for comparison so that the net effects due to hydrogen could be isolated. The samples were analyzed prior to and after exposure. Gas samples were collected in selected experiments and analyzed using gas chromography. Characterization of the resulting microstructure after exposure to hydrogen was conducted using optical microscopy, x-ray diffraction, scanning electron microscopy, and weight change. The ceramics were purchased and were all monolithic in nature. It was found that all samples lost weight after exposure, both in hydrogen and vacuum. Results from the microstructure analyses show that the degradation processes are different among the five types of ceramics involved. In addition, the apparent activation energy for the degradation process is a function of temperature even within the same material. This indicates that there are more than one mechanism involved in each material, and that the mechanisms are temperature dependent.

Zee, Ralph↗
NASA NTRS1996

Hot Hydrogen Exposure Degradation of the Strength of Mullite

This study deals with the corrosion of near stoichiometric mullite (3Al2O3-2SiO2) by pure dry hydrogen gas. Exposure of the mullite samples was at temperatures of 1050 and 1250 C for times up to 500 hours. Preferential attack of the alumino-silicate glass present in the grain boundaries of the mullite occurred after 125 hours at 1250 C. Hydrogen scrubbing of the SiO2 from the glassy grain boundaries and the mullite grains yielded a porous alumina-rich surface. The room temperature strength increased after short exposure times at 1250 C (up to 125 hours), then decreased by 53 percent after exposure for 500 hours. At 1050 C, all exposure times (25 to 500 hours) decreased the strength. After 500 hours in hydrogen at 1050 C, the room temperature strength of mullite decreased 22 percent. We also observed a rapid 25 percent strength loss after short exposure times at 1050 C. This is attributed to the calcium/hydrogen assisted crystallization of the glassy, grain-boundary phase.

Herbell, Thomas P.↗
NASA NTRS2006

Multiphysics Thermal-Fluid Analysis of a Non-Nuclear Tester for Hot-Hydrogen Materials Development

The objective of this effort is to analyze the thermal field of a non-nuclear tester, as a first step towards developing efficient and accurate multiphysics, thermo-fluid computational methodology to predict environments for hypothetical solid-core, nuclear thermal engine thrust chamber design and analysis. The computational methodology is based on a multidimensional, finite-volume, turbulent, chemically reacting, radiating, unstructured-grid, and pressure-based formulation. The multiphysics invoked in this study include hydrogen dissociation kinetics and thermodynamics, turbulent flow, convective, radiative and conjugate heat transfers.

Wang, Ten-See↗
NASA NTRSDate not supplied

Hot Hydrogen Testing of Uranium Nitride Cermet for Nuclear Thermal Propulsion

This study investigated the thermochemical stability and performance characteristics of uranium mononitride tungsten molybdenum cermet (UN-Mo30W) as a potential fuel material for Nuclear Thermal Propulsion (NTP) engines. Twelve monolithic cylinders were subjected to conditions simulating an active NTP engine. The tests demonstrated thermal variability within the test article and highlighted the dissociation of UN into U and N2 at elevated temperatures, affecting the microstructure and causing bonding between cermet wafers and cooling tubes. Findings indicate that while UN-Mo30W cermet exhibits some desirable properties for NTP applications, its suitability is limited by high-temperature thermochemical instability.

nuclear fuels↗
NASA NTRS1981

Charge exchange in the Venus ionosphere as the source of the hot exospheric hydrogen

A global Monte Carlo model of the exosphere of Venus, simulating the normal exospheric processes, as well as the production of a 'hot' hydrogen component by charge exchange of H(+) with H and O, has been computed. The resulting altitude profiles of atomic hydrogen concentration over both the day and night hemispheres are in reasonable agreement with Mariner 5 and Mariner 10 observations of Lyman-alpha, showing that the ionospheric charge exchange reactions are a significant source of 'hot' hydrogen, possibly the dominant source. However, the uncertainties in the available atomic hydrogen data allow for production of a similar amount of nonthermal H by chemical processes involving H2 as suggested by Kumar and Hunten (1974).

Hodges, R. R., Jr.↗
NASA NTRS1992

The constitution of the atmospheric layers and the extreme ultraviolet spectrum of hot hydrogen-rich white dwarfs

An analysis is presented of the atmospheric properties of hot, H-rich, DA white dwarfs that is based on optical, UV, and X-ray observations aimed at predicting detailed spectral properties of these stars in the range 80-800 A. The divergences between observations from a sample of 15 hot DA white dwarfs emitting in the EUV/soft X-ray range and pure H synthetic spectra calculated from a grid of model atmospheres characterized by Teff and g are examined. Seven out of 15 DA stars are found to consistently exhibit pure hydrogen atmospheres, the remaining seven stars showing inconsistency between FUV and EUV/soft X-ray data that can be explained by the presence of trace EUV/soft X-ray absorbers. Synthetic data are computed assuming two other possible chemical structures: photospheric traces of radiatively levitated heavy elements and a stratified hydrogen/helium distribution. Predictions about forthcoming medium-resolution observations of the EUV spectrum of selected hot H-rich white dwarfs are made.

Vennes, Stephane↗
NASA NTRS1972

Erosion of graphite surface exposed to hot supersonic hydrogen gas

A theoretical model based on laminar boundary layer flow equations was developed to predict the erosion rate of a graphite (AGCarb-101) surface exposed to a hot supersonic stream of hydrogen gas. The supersonic flow in the nozzle outside the boundary layer formed over the surface of the specimen was determined by assuming one-dimensional isentropic conditions. An overall surface reaction rate expression based on experimental studies was used to describe the interaction of hydrogen with graphite. A satisfactory agreement was found between the results of the computation, and the available experimental data. Some shortcomings of the model and further possible improvements are discussed.

Sharma, O. P.↗