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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 1,225 records · Page 68
All sourcesNASA NTRSDOE OSTI
NASA NTRS1977

Calculations of the effects of angular momentum on the early evolution of Jupiter

Early phases in the evolutionary development of a rotating cloud of gas and dust are investigated to determine whether physically reasonable initial conditions are likely to produce a planet-satellite system with the values of specific orbital angular momentum currently observed for Jupiter and its inner satellites. Spherically symmetric computations of Jupiter's evolutionary history are reviewed, and transport of angular momentum is considered along with evolutionary sequences of individual differentially rotating models with decreasing values of equatorial radius. The problem of accounting for the present specific orbital angular momenta of Jupiter and its regular satellites is examined qualitatively, and a range of possible angular-momentum distributions in an initially tidally unstable cloud is assessed. The results show that particular physically plausible angular-momentum distributions, which could either be established as initial conditions or be caused by angular-momentum transport, will lead to favorable situations for the formation of a central planet and a surrounding rotating cloud with specific angular momentum comparable to that of the regular satellites.

Bodenheimer, P.↗
NASA NTRS1991

Characterization of a 5-eV neutral atomic oxygen beam facility

An experimental effort to characterize an existing 5-eV neutral atomic oxygen beam facility being developed at Princeton Plasma Physics Laboratory is described. This characterization effort includes atomic oxygen flux and flux distribution measurements using a catalytic probe, energy determination using a commercially designed quadrupole mass spectrometer (QMS), and the exposure of oxygen-sensitive materials in this beam facility. Also, comparisons were drawn between the reaction efficiencies of materials exposed in plasma ashers, and the reaction efficiencies previously estimated from space flight experiments. The results of this study show that the beam facility is capable of producing a directional beam of neutral atomic oxygen atoms with the needed flux and energy to simulate low Earth orbit (LEO) conditions for real time accelerated testing. The flux distribution in this facility is uniform to +/- 6 percent of the peak flux over a beam diameter of 6 cm.

Vaughn, J. A.↗
NASA NTRS1999

Experimental Study of Unsupported Nonane fuel Droplet Combustion in Microgravity

Soot formation in droplet flames is the basic component of the particulate emission process that occurs in spray combustion. The complexity of soot formation motivates a one-dimensional transport condition which has obvious advantages in modeling. Recent models of spherically symmetric droplet combustion have made this assumption when incorporating such aspects as detailed chemistry and radiation. Interestingly, spherical symmetry does not necessarily restrict the results because it has been observed that the properties of carbon formed in flames are not strongly affected by the nature of the fuel or flaming configuration. What is affected, however, are the forces acting on the soot aggregates and where they are trapped by a balance of drag and thermophoretic forces. The distribution of these forces depends on the transport conditions of the flame. Prior studies of spherical droplet flames have examined the droplet burning history of alkanes, alcohols and aromatics. Data are typically the evolution of droplet, flame, extinction, and soot shell diameters. These data are only now just beginning to find their way into comprehensive numerical models of droplet combustion to test proposed oxidation schemes for fuels such as methanol and heptane. In the present study, we report new measurements on the burning history of unsupported nonane droplets in a convection-free environment to promote spherical symmetry. The far-field gas is atmospheric pressure air at room temperature. The evolution of droplet diameter was measured using high speed cine photography of a spark-ignited, droplet within a confined volume in a drop tower. The initial droplet diameters varied between 0.5 mm and 0.6 mm. The challenge of unsupported droplets is to form, deploy and ignite them with minimal disturbance, and then to keep them in the camera field of view. Because of the difficulty of this undertaking, more sophisticated diagnostics for studying soot than photographic were not used. Supporting the test droplet by a fiber fixes the droplet position but the fiber can perturb the burning process especially for a sooting fuel. Prior studies on heptane showed little evidence for soot formation due to g-droplets of similar size the relationship between sooting and droplet diameter. For nonane droplets we expect increased sooting due to the greater number of carbon atoms. As a sooting droplet burns and its diameter decreases, proportionally less soot should form. This reduced soot, as well as the influence of soot formed earlier in the burning process which collects in a 'shell', on heat transport to the flame offers the potential for a time-varying burning rate. Such an effect was investigated and revealed in results reported here. Speculation is offered for the cause of this effect and its possible relation to soot formation.

Callahan, B. J.↗
DOE OSTI2024

An implicit solution for Asay foil trajectories generated by separable, sustained-production ejecta source models

We present a simple implicit solution for the time-dependent trajectory of a thin Asay foil ejecta diagnostic for the general case where the impinging ejecta cloud is generated by a source function characterized by an arbitrary (sustained) time dependence and a time-independent (stationary) particle velocity distribution. In the limit that the source function time dependence becomes a delta function, this solution—which is amenable to rapid numerical calculations of arbitrary accuracy—exactly recovers a previously published solution for the special case of instantaneous ejecta production. We also derive simple expressions for the free-surface arrival (catch-up) time as well as the true ejecta areal mass accumulation on the accelerating foil and place bounds on the level of error incurred when applying instant-production mass solutions to a sustained-production trajectory. We demonstrate these solutions with example calculations for hypothetical source functions spanning a wide range of ejecta production durations, velocity distributions, and temporal behaviors. These calculations demonstrate how the foil trajectory is often insensitive to the temporal dependence of the source function, instead being dominated by the velocity distribution. We quantify this insensitivity using a “compatibility score” metric. Under certain conditions, one may capitalize upon this insensitivity to obtain a good approximation of the second integral of the velocity distribution from the observed foil trajectory.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2024

Modeling of H2 Dispersion at ARIES

Hydrogen is a versatile and clean energy carrier that can be produced from various renewable sources such as wind, solar, and hydropower and help decarbonize electricity grids, industry, and transportation. Using the Hydrogen Research Facility under Advanced Research on Integrated Energy Systems (ARIES) at the National Renewable Energy Laboratory's (NREL) Flatirons campus as a test bench, the study examines the feasibility, useability, and value of using computational fluid dynamics (CFD) techniques to model hydrogen dispersion. The ARIES facility was chosen because controlled hydrogen releases can be performed at a rate of 27 kg-H2/hr. Site-specific atmospheric and weather condition data such as wind speed and temperature were used as inputs to the model. The results show statistical distributions and ranges of hydrogen concentrations at locations throughout the domain. Wind conditions are found to significantly impact the release behavior, including the hydrogen cloud's direction and concentrations. At low wind speeds (below 1 mph), hydrogen forms a cloud and at higher wind speeds (> 2-4 mph) hydrogen plume stretches in the direction of wind momentum. From >100 simulations for ARIES site-specific conditions, statistical quantities combined with a clustering algorithm were used to propose sensor location at various elevations from ground.

dispersion↗
DOE OSTI2026

Plutonium Retention by Crystalline Silicotitanate under Hyperalkaline Conditions Relevant to Tank-Side Cesium-Removal at the Hanford Site

Crystalline silicotitanate (CST) is used in Hanford’s Tank-Side Cesium-Removal (TSCR) process to selectively remove Cs-137 from highly caustic, nitrate-rich tank supernatants. Recent testing with actual waste samples suggests that CST can also retain measurable plutonium (Pu), which could affect radiological classification and disposal pathways for spent CST. To quantify this behavior, Pu partitioning to CST was studied under Hanford-relevant conditions using batch-contact experiments in a representative simulant (2 M NaNO3, 0.7 M NaOH). Isotherm data were measured and distribution ratios calculated, with Cs+ uptake used as benchmark. Under low-carbonate conditions, Pu was retained strongly by CST in systems initially contacted with either PuO2 nanoparticles (Pu(IV)) or aqueous Pu(VI), with distribution ratios of ~2,200–3,700 mL/g, generally exceeding those for Cs+ (~400–1,000 mL/g). Increasing carbonate concentration strongly reduced PuO2 nanoparticle retention; at [Na2CO3] = 1 M, distribution ratios decreased by up to one order of magnitude to roughly 100–300 mL/g. Electron microscopy suggests that Pu retention involves a combination of mechanisms such as PuO2 NP aggregation induced by CST leachate components, and association with CST bead surfaces.

Neumann, J.↗
NASA NTRS1993

Origin, transport, and losses of energetic He(+) and He(2+) ions in the magnetosphere of the Earth - AMPTE/CCE observations

Data from the ion charge-energy-mass spectrometer CHEM flown on AMPTE/CCE spacecraft are used to investigate the origin, transport, and losses of energetic He(+) and He(2+) ions in the earth's magnetosphere. The L profiles of the average ion phase space density f were determined as a function of the magnetic momentum. It is shown that the L profiles have an inner part, where f increases with L for both He(+) adn He(2+) and where steady-state conditions are fulfilled. The outer boundary L(lim) of this region is located at a distance that depends on the ion species and the geomagnetic activity level. Steady-state conditions continue outside L(lim) for He(+) ions, while the He(2+) ion distribution outside L(lim) is strongly influenced by ion convection causing a lack of steady-state conditions. It is concluded that solar wind is the origin of the He(2+), while a mixed origin is suggested for the He(+) ions, in which the major contribution is from the solar wind via charge exchange production from the He(2+) ions.

Kremser, G.↗
DOE OSTI2025

Solving high-dimensional inverse problems using amortized likelihood-free inference with noisy and incomplete data

Here, we present a likelihood-free probabilistic inversion method based on normalizing flows for high-dimensional inverse problems. The proposed method is composed of two complementary networks: a summary network for data compression and an inference network for parameter estimation. The summary network encodes raw observations into a fixed-size vector of summary features, while the inference network generates samples of the approximate posterior distribution of the model parameters based on these summary features. The posterior samples are produced in a deep generative fashion by sampling from a latent Gaussian distribution and passing these samples through an invertible transformation. We construct this invertible transformation by sequentially alternating conditional invertible neural network and conditional neural spline flow layers. The summary and inference networks are trained simultaneously. We apply the proposed method to an inversion problem in groundwater hydrology to estimate the posterior distribution of the log-conductivity field conditioned on spatially sparse time-series observations of the system’s hydraulic head responses. The conductivity field is represented with 706 degrees of freedom in the considered problem. Comparison with the likelihood-based iterative ensemble smoother PEST-IES method demonstrates that the proposed method accurately estimates the parameter posterior distribution and the observations’ predictive posterior distribution at a fraction of the inference time of PEST-IES.

conditional invertible neural network↗
NASA NTRS2002

Use of Traffic Intent Information by Autonomous Aircraft in Constrained Operations

This paper presents findings of a research study designed to provide insight into the issue of intent information exchange in constrained en-route air-traffic operations and its effect on pilot decision-making and flight performance. The piloted simulation was conducted in the Air Traffic Operations Laboratory at the NASA Langley Research Center. Two operational modes for autonomous flight management were compared under conditions of low and high operational complexity (traffic and airspace hazard density). The tactical mode was characterized primarily by the use of traffic state data for conflict detection and resolution and a manual approach to meeting operational constraints. The strategic mode involved the combined use of traffic state and intent information, provided the pilot an additional level of alerting, and allowed an automated approach to meeting operational constraints. Operational constraints applied in the experiment included separation assurance, schedule adherence, airspace hazard avoidance, flight efficiency, and passenger comfort. The strategic operational mode was found to be effective in reducing unnecessary maneuvering in conflict situations where the intruder's intended maneuvers would resolve the conflict. Conditions of high operational complexity and vertical maneuvering resulted in increased proliferation of conflicts, but both operational modes exhibited characteristics of stability based on observed conflict proliferation rates of less than 30 percent. Scenario case studies illustrated the need for maneuver flight restrictions to prevent the creation of new conflicts through maneuvering and the need for an improved user interface design that appropriately focuses the pilot's attention on conflict prevention information. Pilot real-time assessment of maximum workload indicated minimal sensitivity to operational complexity, providing further evidence that pilot workload is not the limiting factor for feasibility of an en-route distributed traffic management system, even under highly constrained conditions.

Wing, David J.↗
NASA NTRS1978

Geoid Anomalies and the Near-Surface Dipole Distribution of Mass

Although geoid or surface gravity anomalies cannot be uniquely related to an interior distribution of mass, they can be related to a surface mass distribution. However, over horizontal distances greater than about 100 km, the condition of isostatic equilibrium above the asthenosphere is a good approximation and the total mass per unit column is zero. Thus the surface distribution of mass is also zero. For this case we show that the surface gravitational potential anomaly can be uniquely related to a surface dipole distribution of mass. Variations in the thickness of the crust and lithosphere can be expected to produce undulations in the geoid.

Turcotte, D. L.↗
NASA NTRS1987

Particle trajectory computer program for icing analysis of axisymmetric bodies - A progress report

Aircraft exposed to an atmospheric icing environment can accumulate ice, resulting in a sharp increase in drag, a reduction in lift, control surface fouling, and engine damage all of which result in a hazardous flight situation. NASA Lewis Research Center (LeRC) has conducted a program to examine, with the aid of high-speed computer codes, how the trajectories of particles contribute to the ice accumulation on airfoils and engine inlets. For this effort, a computer code was developed to calculate icing particle trajectories and impingement limits for axisymmetric inlets. The original research-oriented NASA code was upgraded and modified to meet the requirements of the design engineer. The improved code is capable of performing trajectory calculations for any atmospheric conditions and droplet sizes. It can handle single droplets or a distribution of various droplet sizes. The four programs that comprise the code are described and the results of a test case using flight conditions for a Fokker F100 icing tunnel test are presented.

Maltezos, Dimitrios G.↗
NASA NTRS1974

Sequential cumulative fatigue reliability

A component is assumed to be subjected to a sequence of several groups of sinusoidal stresses. Each group consists of a specific number of cycles having the same maximum alternating stress level and the same mean stress level, the maximum alternating stress level being different from group to group. A method for predicting the reliability of components subjected to such loads is proposed, given their distributional alternating stress versus cycles-to-failure (S-N) diagram. It is called the 'conditional reliability-equivalent life' method. It is applied to four-cases using distributional fatigue data generated in the Reliability Research Laboratory of The University of Arizona, and the predicted reliabilities are compared and discussed.

Kececioglu, D.↗
NASA NTRS2001

Testing of a Loop Heat Pipe with Two Evaporators and Two Condensers

Most existing Loop Heat Pipes (LHPs) consist of one single evaporator and one single condenser. LHPs with multiple evaporators will be very desirable for cooling multiple heat sources or a heat source with large thermal footprints. Extending the LHP technology to include multiple evaporators and multiple condensers faces some challenges, including the interaction between individual compensation chambers, operating temperature stability, and adaptability to rapid power and sink temperature transients. This paper describe extensive testing of an LHP with two evaporators and two condensers. Tests performed include start-up, power cycle, sink temperature cycle, reservoir temperature cycle, and capillary limit. Test results showed that the loop could operate successfully under various heat load and sink conditions. The loop operating temperature is a function of the total heat load, the heat load distribution between the two evaporators, and temperatures of the two condenser sinks. Under most conditions, only one reservoir contained two-phase fluid and the other reservoir was completely liquid filled. Moreover, control of the loop operating temperature could shift from one reservoir to the other as the test condition changed.

Ku, Jentung↗
NASA NTRS2023

Evaluation of Elements used for Manufacturing of NanoLam Metallized Polymer Film Capacitors

Metallized polymer film capacitors (MPFC) manufactured by NanoLam technology have a better volumetric efficiency and performance that may exceed the reliability of conventional MPFCs typically used in power and high voltage systems that require high insulation resistance and low power losses. These capacitors can be also an effective replacement for electrolytic and stacked ceramic capacitors currently used in space applications looking to save significant volume and mass. This report evaluates the effects of environmental conditions including radiation and storage at room and high temperatures on the characteristics of NanoLam elements used in the production of MPFCs. Assessments of the reliability acceleration factors and predictions for the useful life are made based on highly accelerated life tests (HALT) using distributions of times to parametric failures at different stress conditions. It has been shown that even a relatively small amount of moisture absorbed at room environments in the dielectric layers may substantially change the probability of failure. In the presence of moisture, degradation processes that started after voltage application continue with time during storage.

Metallized polymer film capacitors (MPFC)↗
DOE OSTI2023

Modeling of Stress Distribution in Molten Salt Thermal Energy Storage Tanks for In-Service Central Receiver Power Plants

Failures in molten nitrate salts thermal energy storage tanks (TES) have been occurring in several concentrating solar power (CSP) plants around the world after a few months or years of operation. These failures are mainly related to a combination of high stress, corrosion, large deformation, and thermal cycling. Most of these failures are a consequence of the infancy of this technology; technical standards for design, fabrication, implementation, and operation of molten salt tanks operating at temperatures up to 565 degrees Celsius do not exist and most of current in-service tanks have been designed using the recommendations from the American Petroleum Institute (API) 650 and the American Society of Mechanical Engineers ASME section II standards, which are applicable for TES tanks operating at lower temperatures. We have developed a 3-dimensional model of a representative molten salt hot tank design that uses typical CSP plant operation conditions and allows determining the temperature and stress distribution in the tank. The model also considers the initial floor residual stresses and distortion after its welding fabrication. We have identified critical thermal gradients in the tank floor and shell and locations in the tank where the stresses are high and could become susceptible points for failure.

concentrating solar power↗
NASA NTRS1989

Angular dependent transport of auroral electrons in the upper atmosphere

The transport of auroral electrons through the upper atmosphere is analyzed. The transport equation is solved using a discrete-ordinate method, including elastic and inelastic scattering of electrons (resulting in changes of pitch angle) and degradation in energy as the electrons penetrate into the atmosphere. The transport equation is solved numerically for the electron intensity as a function of altitude, pitch angle, and energy. In situ measurements of the pitch angle and energy distribution of precipitating electrons over an auroral arc provide boundary conditions for the calculation. Model calculations were carried out with various different phase functions for elastic and inelastic collisions to attempt changing the angular scattering, but the observed pitch angle distributions remain unexplained. It is suggested that mechanisms other than collisional scattering influence the angular distribution of auroral electrons at or below 300 km altitude in the low-energy domain.

Lummerzheim, D.↗
NASA NTRS2000

The Axisymmetric Pulsar Magnetosphere

We present the structure of the axisymmetric force-free magnetosphere of an aligned rotating magnetic dipole, in the case in which there exists a sufficiently large charge density (whose origin we do not question) to satisfy the ideal MHD condition, E (raised dot) B = 0, everywhere. The unique distribution of electric current along the open magnetic field lines which is required for the solution to be continuous and smooth is obtained numerically. We expect that our solution will be useful as the starting point for detailed studies of pulsar magnetospheres under more general conditions, namely when either the force-free and/or the ideal MHD condition E (raised dot) B = 0 are not valid in the entire magnetosphere. Based on our solution, we consider that the most likely positions of such an occurrence are the polar cap, the crossings of the zero space charge surface by open field lines, and the return current boundary, but not the light cylinder.

Contopoulos, J.↗