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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 127 records · Page 7
All sourcesNASA NTRSDOE OSTI
NASA NTRS1961

Stability of Titanium Nitride and Titanium Carbide When Exposed to Hydrogen Atoms from 298 to 1950 K

Titanium nitride and titanium carbide deposited on tungsten wires were exposed to hydrogen atoms (10(exp -4) atm pressure) produced by the action of microwave radiation on molecular hydrogen. The results of these experiments in the temperature range 298 to 1950 K indicate that no appreciable reaction takes place between atomic hydrogen and TiN or TiC. The formation of reaction products (NH3, CH4, C2H2) should be favored at lower temperatures. However, because of the high catalytic activity of Ti for H atom recombination, the rate of such reactions with H atoms is controlled by the rate of evaporation of Ti from the surface, this rate being low at temperatures below 1200 K. In order to interpret the stability of TiN and TiC in H atoms more fully, the stability of TiN and TiC in vacuum and H2 gas was also studied. The thermodynamic computations conform in order of magnitude to the experimentally found rates of decomposition of TiN and TiC in vacuum and are also consistent with the fact that no appreciable reaction is found with these compounds in molecular H2 at a pressure of 10(exp -3) atmosphere in the temperature range 2980 to 2060 K. When TiN or TiC was heated in atomic H or molecular H2, no reaction products other than those obtained from the simple decomposition of the nitride and carbide were observed. The gaseous products were analyzed in a mass spectrometer.

Philipp, Warren H.↗
NASA NTRS1998

Dynamics of Liquids in Edges and Corners (DYLCO): IML-2 Experiment for the BDPU

Knowledge of the behavior of fluids possessing free surfaces is important to many fluid systems, particularly in space, where the normally subtle effects of surface wettability play a more dramatic and often surprising role. DYLCO for the IML-2 mission was proposed as a simple experiment to probe the particular behavior of capillary surfaces in containers of irregular cross section. Temperature control was utilized to vary the fluid-solid contact angle, a questionable thermodynamic parameter of the system, small changes in which can dramatically influence the configuration, stability, and flow of a capillary surface. Container shapes, test fluid, and temperature ranges were selected for observing both local changes in interface curvature as well as a global change in fluid orientation due to a critical wetting phenomenon. The experiment hardware performed beyond what was expected and fluid interfaces could be readily digitized post flight to show the dependence of the interface curvature on temperature. For each of the containers tested surfaces were observed which did not satisfy the classic equations for the prediction of interface shape with constant contact angle boundary condition. This is explained by the presence of contact angle hysteresis arising from expansion and contraction of the liquid during the heating and cooling steps of the test procedure. More importantly, surfaces exceeding the critical surface curvature required for critical wetting were measured, yet no wetting was observed. These findings are indeed curious and pose key questions concerning the role of hysteresis for this critical wetting phenomena. The stability of such surfaces was determined numerically and it is shown that stability is enhance (reduced) when a surface is in its 'advancing' ('receding') state, The analysis shows complete instability as the critical wetting condition is reached. The case of ideal dynamic wetting is addressed analytically in detail with results of significant flow characteristics presented in closed form. The solutions indicate a square root of T dependence of the capillary 'rise' rate which is corroborated by drop tower tests. The analysis clearly shows that infinite time is necessary for surfaces to reorient at the critical wetting transition.

Langbein, D.↗
NASA NTRS2019

Evaluation of the Antarctic Boundary Layer Thermodynamic Structure In MERRA2 Using Dropsonde Observations from the Concordiasi Campaign

Recent high-resolution dropsonde observations from the 2010 Concordiasi field campaign in austral spring season show that surface-based inversions (SBIs) over Antarctica are frequently eroded, with well-mixed boundary layers occurring 33% and 18% of the time in West and East Antarctica, respectively. In this study, using the dropsonde observations, we evaluate the performance of the Modern-Era Retrospective analysis for Research and Applications, version 2 (MERRA2) in representing the Antarctic boundary layer thermodynamic structure. Results show that MERRA2 has a good overall representation of the Antarctic surface stability and correctly predicts 82% of the SBIs. However, an under prediction of less stable boundary layer occurrence, especially over the elevated East Antarctic plateau, is favored during conditions of increased lower tropospheric stability associated with model dynamics, indicating difficulty in parameterizing turbulence in very stable boundary layers. In addition, a lower tropospheric cool bias (first model level and above) is observed in the MERRA2 reanalysis, especially over West Antarctica, which amplifies in the boundary layer during mixed conditions. The near-surface cold bias is most pronounced when the model fails to predict mixed layers over West Antarctica, and is expected to negatively impact the representation of surface energy budget and melt processes.

Manisha Ganeshan↗
NASA NTRS1992

Thermodynamics, Solubility, and Diffusivity of Oxygen in Titanium and Ti-Al Alloys

Titanium aluminides and titanium aluminide-based composites are attractive candidate materials for high-temperature structural applications. As these materials may be exposed to oxidizing environments durine their use at elevated temperatures, it is essential that they possess a good oxidation resistance. Previous studies have shown that the oxidation resistance of Al-rich alloys in the Ti-Al system is superior to that of the Ti-rich alloys. The scales formed on the surface of the Al-rich and Ti-rich alloys have been reported to be predominantly Al2O3 and TiO2, respectively. Since the relative stabilities of the oxides of Al and Ti at various temperatures and oxygen pressures can be assessed from their thermodynamic data, it is possible, With the help of thermodynamic calculations, to determine the compositions of the alloys which would form scales of Al2O3, TiO(x) or a ternary oxide such as TiAl2O5 during oxidation at a given temperature. The thermodynamic calculations require reliable activity data for the Ti-Al system. These data have not been determined for the entire composition and temperature range of interest. Using the data available in the literature, recently performed thermodynamic calculations and concluded that the stable oxide changed from TiO to Al2O3 in the existence region of the tial phase. In the case of titanium aluminide-based composites, another major concern is the mutual chemical compatibility of the matrix material with the reinforcement phase. Fibers of SiC, TiB2 and Al2O3 are currently being investigated for reinforcement of titanium aluminide matrices.

Mehrotra, Gopal M.↗
NASA NTRSDate not supplied

Uncertainty Quantification of Classical Theories of Dendritic Growth Kinetics Applied to Nickel-Based Alloys

The solidification velocity in a model nickel-alloy single crystal during laser spot melting was recently characterized using synchrotron X-ray imaging. The measured solidification velocity was found to exceed the absolute stability threshold predicted by the Kurz-Giovanola-Trivedi (KGT) model. The discrepancies between the model and experiments motivate the further assessment of accurate material properties. This work quantifies the impact material property uncertainty has on model predictions of the absolute stability threshold velocities. Properties from the literature are reviewed and compared to those calculated using computational thermodynamics to provide uncertainty estimates on input properties to the KGT model. Global sensitivity analysis is used to quantify the influence of each uncertain input property on the predicted threshold velocity. This work supports the understanding of the nickel-alloy solidification during powder bed fusion additive manufacturing and identifies the solidification material properties that are the most important to assess from first-principles computations and experiments.

Computational thermodynamics↗
NASA NTRS2020

Computational Design of Eutectic Molten Salt Mixtures: What Can Thermodynamic Models Do?

In the search for efficient energy storage battery technologies, designing stable electrolytes has been a long-standing challenge. Electrolytes based on molten salt eutectics are known for their stability with minimum parasitic reactions when compared to their widely used organic counterparts. However, the operating temperatures of these molten salt electrolyte-based batteries are dictated by the melting point of the eutectic mixtures. Design and high throughput screening of low melting temperature eutectic molten salt mixtures have been hindered by the lack of computational models. In this work, we develop thermodynamic models to predict the eutectic points of several molten salt mixtures. The framework of the COSMO-SAC model is used for the predictions and is compared with experimental data and other thermodynamic approaches. Rapid thermodynamics-based approaches, as shown in this study, can accelerate the discovery of new materials, complementing experimental techniques.

Ashwin Ravichandran↗
NASA NTRS1971

Vacuum ultraviolet radiometry with a stabilized hydrogen arc.

Use of the spectral radiation emitted from a dense hydrogen plasma of at least 12,000 K, which is in local thermodynamic equilibrium (LTE), as a light source for vacuum UV radiometry. Its spectroscopic qualities are exactly known, and except for a few strongly Stark-broadened Lyman lines, its spectrum in the vacuum UV is essentially continuous. The calculated continuum output of this source for typical operating conditions is compared with the UV output of the tungsten strip lamp and the carbon arc.

Ott, W. R.↗
NASA NTRS1991

Entropy-Based Approach To Nonlinear Stability

NASA technical memorandum suggests schemes for numerical solution of differential equations of flow made more accurate and robust by invoking second law of thermodynamics. Proposes instead of using artificial viscosity to suppress such unphysical solutions as spurious numerical oscillations and nonlinear instabilities, one should formulate equations so that rate of production of entropy within each cell of computational grid be nonnegative, as required by second law.

Merriam, Marshal L.↗
NASA NTRS1973

Heat pipe stability. 1: A preliminary investigation into thermally assisted cavitation

The notion is introduced of thermally assisted cavitation by localized fluctuations in capillary forces. Because cavitation in liquids can be closely approximated by an isothermal process, only momentum and mass balances are used to introduce the notion for liquids under mechanical tension. Brief attention is given to developing a stability theory in terms of the stiffness and compliance coefficients for a working fluid. Interestingly, the particular thermodynamic approach taken can be used to suggest experiments relating working fluid performance to meniscus behavior. A correction to the liquid flow equation is suggested.

Source record↗
NASA NTRS1991

The density temperature and the dry and wet virtual adiabats

A density temperature is introduced to represent virtual temperature and potential temperature on thermodynamic diagrams. This study reviews how the dry and wet virtual adiabats can be used to represent stability and air parcel density for unsaturated and cloudy air, and present formula and tabulations.

Bartlo, J.↗
NASA NTRS2000

Directionally Solidified Ceramics Produced

Produced Multiphase, interpenetrating structures are an alternative route to obtaining structural ceramic materials with adequate strength, toughness, and stability for high-temperature aerospace applications. The eutectic architecture, a continuous-reinforcing phase within a higher volume phase or matrix, can be described as a naturally occurring, in situ composite. The phases of a eutectic are thermodynamically compatible at high homologous temperatures. Strong and stable materials have been produced. Toughness, however, remains a technical obstacle. The potential for producing materials with enhanced toughness along with adequate strength and stability was demonstrated using the laser-heated float zone (LHFZ) growth method at the NASA Glenn Research Center at Lewis Field. LHFZ growth at Glenn provides a means to efficiently produce and record the underlying growth phenomena associated with two-phase structures. To initiate directional solidification, a seed of single-crystal sapphire (<0001> direction) was lowered onto the molten liquid until wetting occurred and then withdrawn at a constant rate. Neither the crystal nor the source rod was rotated. The materials produced were tested mechanically in tension, and the resulting microstructure was examined with a scanning electron microscope. Both the inherent properties of the constituent phases and the properties of the interface between them affect the mechanical behavior and the fracture surfaces. The following scanning electron micrographs show the microstructures of two different materials that were tested to failure in tension. In the left micrograph, the flat fracture surface is typical of a material that is strong but has low toughness. In the right micrograph, the crack is effectively deflected at the interface between the two phases, achieving higher toughness at moderately lower strength levels. Conducting mechanical tests to determine the high temperature properties of these materials is the next step in determining their eventual suitability.

Farmer, Serene C.↗
NASA NTRSDate not supplied

Enabling Nuclear and Solar Thermal Propulsion with the Computational Laboratory: Faster and Cheaper Materials Characterization

Nuclear and solar thermal propulsion offer enhanced efficiencies for in-space travel which may open up the outer Solar System to both crewed and automated craft. However, these advanced propulsion systems require cutting-edge materials which are often not easily tested in the laboratory. Ab initio thermodynamics and other computational methods offer a way to test materials at high pressures and temperatures more quickly, and with reduced cost. Here, several case studies are presented which highlight the utility of modern simulation techniques. First, an extensive thermodynamic study was performed at the ab initio level to elucidate the role of hot hydrogen flow on the erosion of four refractory carbides to examine their appropriateness for use as channel coatings. A detailed analysis of reaction products informs estimates of erosion which are validated in comparison with heritage NERVA data. Specific material suggestions are made for both nuclear and solar designs. Secondly, we examined the mechanical behavior and chemical stability of various components of an idealized nuclear cermet core design using techniques spanning from the atomic to microscale. Next, the mechanical and chemical behavior of tungsten (a potential matrix material) and the stability of uranium mononitride (a potential ceramic fuel element), are characterized in the presence of hydrogen and at elevated temperatures with ab initio thermodynamics. Finally, the mechanical response and failure of tungsten under tensile strain is simulated at the micron scale with a combined finite element and dislocation dynamics approach. The resultant stress-strain data agrees well with experiments and leads to a workflow which can incorporate ab initio thermodynamic data into micron-scale simulations and thus provide real-world relevant estimates of erosion and stress-strain behavior. The power of this framework and our plans to use it in the future will be discussed.

William C Tucker↗
NASA NTRSDate not supplied

Designing Molten Salt Eutectics: A Combined Thermodynamic Modeling and Machine Learning Approach

Designing stable electrolytes with target properties is an important challenge in realizing next generation energy storage devices. Molten salt eutectics-based electrolytes are known for their stability with minimal parasitic reactions when compared to traditional organic electrolytes and are an attractive option for different battery chemistries. The operating temperature of the molten salt batteries depends on the melting temperature of the eutectic and hence there is a necessity to discover novel low melting temperature molten salt eutectic mixtures for energy storage applications. In this work we develop a high throughput computational screening approach for molten salt mixtures using thermodynamic modeling and machine learning (ML). COSMO-SAC model and ML approaches were independently developed based on the existing experimental data and these models were further used to predict the eutectic melting temperature and composition of several new binary, ternary, and quaternary mixtures. We show that combining ML and thermodynamic modeling strategies is effective in exploring the vast design space of molten salt mixtures.

Thermodynamics↗
NASA NTRSDate not supplied

Understanding Thermal Stability in Zirconia-Based Aerogels

For lightweight, thermal insulation needs above 1000ºC, the high surface to volume ratios of ceramic-based aerogels are practically unparalleled. Yet realizing the full potential of aerogel-based thermal protection systems requires not only increased thermal stability, but also a broadened menu of stabilizing mechanisms. Here we will review our recent efforts to understand the impact of synthetic parameters and dopant chemistry on the evolution of zirconia-based ceramics. A broad parametric window for thermal stability is established, in which the more sensitive variable of composition has been probed. However, dopant chemistry is actually an aggregate for many closely related material parameters including surface energy, enthalpy of formation, each of which may contribute uniquely to aerogel destabilization. A truly predictive design framework for ceramic-based aerogels requires further decoupling of these underlying properties through systematic and comprehensive evaluation of thermodynamic properties.

aerogel↗
NASA NTRS1994

Chemical models of the deep atmospheres of Jupiter and Saturn

New and updated chemical kinetic data, elemental abundances, and thermodynamic data are used for thermochemical equilibrium and, where relevant, thermochemical kinetic calculations of gas abundances and condensate stability in the hot, deep atmospheres of Jupiter and Saturn. Over 2000 compounds of all naturally occurring elements in the periodic table are considered. The calculations range from 298 to 2000 K and are done for adiabatic models of the two planetary atmospheres. The results predict the abundances of many gases which are potentially observable by the Galileo probe to Jupiter, by the Cassini mission to Saturn, and by Earth-based and Earth-orbital telescopes. In addition, the results also predict many new species which are potentially observable by a new generation of entry probes capable of penetrating deeper into the atmospheres of Jupiter and Saturn.

Fegley, Bruce, Jr.↗
NASA NTRS2010

Propellant Readiness Level: A Methodological Approach to Propellant Characterization

A methodological approach to defining propellant characterization is presented. The method is based on the well-established Technology Readiness Level nomenclature. This approach establishes the Propellant Readiness Level as a metric for ascertaining the readiness of a propellant or a propellant combination by evaluating the following set of propellant characteristics: thermodynamic data, toxicity, applications, combustion data, heat transfer data, material compatibility, analytical prediction modeling, injector/chamber geometry, pressurization, ignition, combustion stability, system storability, qualification testing, and flight capability. The methodology is meant to be applicable to all propellants or propellant combinations; liquid, solid, and gaseous propellants as well as monopropellants and propellant combinations are equally served. The functionality of the proposed approach is tested through the evaluation and comparison of an example set of hydrocarbon fuels.

Bossard, John A.↗
NASA NTRSDate not supplied

Dissecting the Roles of Stability and Dynamic Regimes in Tropical Cloud Feedbacks Simulated from an Upgraded Multiscale Modeling Framework (MMF)

In this study, we analyze the tropical cloud feedback from a 2 K sea surface temperature perturbation experiment performed with a multiscale modeling framework (MMF). We sort the monthly-mean cloud and radiative properties according to circulation and stability regimes. It is found that the dynamic component of cloud feedback for a given dynamic regime dominates the thermodynamic component in terms of the absolute magnitude.

Kuan-Man Xu↗
NASA NTRSDate not supplied

Molten Salt Electrolytes: Computational Analysis of Transport, Electrochemical Properties and Designing New Mixtures

Electric aircraft propulsion has gained a traction over the last decade due to possible high-energy density electrochemistries with reasonable cycle life and identification of non-flammable chemistries that can guarantee much better safety. Commercial Li-ion batteries cannot reach such high capacities because of weight limitations that arise from the widely used intercalation electrodes. Also, use of organic electrolytes make them highly susceptible to fire on exposure to air and humidity. Currently, use of Lithium metal anode along with conversion electrochemistries such as Li-O2 and Li-S are being pursued to achieve such high energy densities. Safer inorganic solid-state electrolytes, recently discovered Water-in-Salt electrolytes, molten salt electrolytes are some of the alternatives being pursued for a safer/non-flammable battery. Of these safer alternatives, molten-salt electrolytes offer some attractive properties: liquid at operating temperatures resulting in better electrode-wetting, stable interface with Li-metal anodes and good ionic conductivity; their only drawback being high operating temperatures. In this talk, we will discuss some of the computational studies, driven via atomistic simulations, of the properties of molten-salt electrolytes including transport mechanism and interface stability. We will also discuss predicting electrochemical properties of these high-temperature electrolytes. Further, we will discuss a thermodynamic approach to predicting new molten-salt eutectics with lower melting points.

Molten Salt Electrolytes↗