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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 1,783 records · Page 99
All sourcesNASA NTRSDOE OSTI
DOE OSTI2024

A Century of Reforestation Reduced Anthropogenic Warming in the Eastern United States

Abstract Restoring and preserving the world's forests are promising natural pathways to mitigate some aspects of climate change. In addition to regulating atmospheric carbon dioxide concentrations, forests modify surface and near‐surface air temperatures through biophysical processes. In the eastern United States (EUS), widespread reforestation during the 20th century coincided with an anomalous lack of warming, raising questions about reforestation's contribution to local cooling and climate mitigation. Using new cross‐scale approaches and multiple independent sources of data, we uncovered links between reforestation and the response of both surface and air temperature in the EUS. Ground‐ and satellite‐based observations showed that EUS forests cool the land surface by 1–2°C annually compared to nearby grasslands and croplands, with the strongest cooling effect during midday in the growing season, when cooling is 2–5°C. Young forests (20–40 years) have the strongest cooling effect on surface temperature. Surface cooling extends to the near‐surface air, with forests reducing midday air temperature by up to 1°C compared to nearby non‐forests. Analyses of historical land cover and air temperature trends showed that the cooling benefits of reforestation extend across the landscape. Locations surrounded by reforestation were up to 1°C cooler than neighboring locations that did not undergo land cover change, and areas dominated by regrowing forests were associated with cooling temperature trends in much of the EUS. Our work indicates reforestation contributed to the historically slow pace of warming in the EUS, underscoring reforestation's potential as a local climate adaptation strategy in temperate regions.

Environmental Sciences & Ecology↗
DOE OSTI2021

Arctic tundra shrubification: a review of mechanisms and impacts on ecosystem carbon balance

Abstract Vegetation composition shifts, and in particular, shrub expansion across the Arctic tundra are some of the most important and widely observed responses of high-latitude ecosystems to rapid climate warming. These changes in vegetation potentially alter ecosystem carbon balances by affecting a complex set of soil–plant–atmosphere interactions. In this review, we synthesize the literature on (a) observed shrub expansion, (b) key climatic and environmental controls and mechanisms that affect shrub expansion, (c) impacts of shrub expansion on ecosystem carbon balance, and (d) research gaps and future directions to improve process representations in land models. A broad range of evidence, including in-situ observations, warming experiments, and remotely sensed vegetation indices have shown increases in growth and abundance of woody plants, particularly tall deciduous shrubs, and advancing shrublines across the circumpolar Arctic. This recent shrub expansion is affected by several interacting factors including climate warming, accelerated nutrient cycling, changing disturbance regimes, and local variation in topography and hydrology. Under warmer conditions, tall deciduous shrubs can be more competitive than other plant functional types in tundra ecosystems because of their taller maximum canopy heights and often dense canopy structure. Competitive abilities of tall deciduous shrubs vs herbaceous plants are also controlled by variation in traits that affect carbon and nutrient investments and retention strategies in leaves, stems, and roots. Overall, shrub expansion may affect tundra carbon balances by enhancing ecosystem carbon uptake and altering ecosystem respiration, and through complex feedback mechanisms that affect snowpack dynamics, permafrost degradation, surface energy balance, and litter inputs. Observed and projected tall deciduous shrub expansion and the subsequent effects on surface energy and carbon balances may alter feedbacks to the climate system. Land models, including those integrated in Earth System Models, need to account for differences in plant traits that control competitive interactions to accurately predict decadal- to centennial-scale tundra vegetation and carbon dynamics.

54 ENVIRONMENTAL SCIENCES↗
NASA NTRS1971

A thermosphere composition measurement using a quadrupole mass spectrometer with a side energy focussing quasi-open ion source

The atomic oxygen concentration in the altitude range 130 to 240 km was determined through the use of a quadrupole spectrometer with a strongly focussing ion source. The instrument is used in the Thermosphere Probe in a manner that greatly increases the proportion of measured oxygen ions that have not experienced a surface collision and permits quantitative evaluation of surface recombination and thermalization effects which inevitably enter all spectrometer determinations. The data obtained strengthen the concept that consideration of surface effects is significant in quantifying spectrometer measurements of reactive gases, and tend to be in agreement with von Zahn's recent results.

Niemann, H. B.↗
NASA NTRS1972

Radiant heat transfer between nongray directional surfaces.

Real surface property effects on local and overall heat transfer are studied for a simple system of interacting opaque surfaces. Wavelength, temperature and directional dependence of surface properties is included in the analysis for equal and unequal temperature specularly reflecting surfaces. Tungsten is employed as a representative metal and Roberts' model is used to describe the wavelength and temperature dependence of its optical parameters. The relationships of electromagnetic theory are employed to describe the directional dependence of spectral properties. Numerical results establish that gray direction independent property analysis adequately predicts the general trends of real surface analysis. The results also establish that spectral and temperature dependence of surface properties influences radiant heat transfer to a greater degree than does directional dependence of properties. Property models which adequately account for the nongray character of engineering surfaces while neglecting directional dependence of properties can provide heat transfer results of acceptable engineering accuracy.

Fischer, W. D.↗
NASA NTRS1989

Modelling asteroid brightness variations. II - The interpretability of light curves and phase curves

Light curves and phase curves have been computed for various asteroid models using the Lumme-Bowell (1981) scattering law. The effects of the scattering parameters on light curves were found to be almost negligible for homogeneous surfaces. The effects on phase curves were more distinct, but changing any of the scattering parameters affects the phase curves in a very similar way, making it impossible to find a unique set of parameter values corresponding to a given phase curve. Light curve amplitudes, on the other hand, depend very strongly on body shape. At least in the case of a triaxial ellipsoid it is possible to determine the axial ratios. Some observed irregularities of light curves can also be modelled easily, but the uniqueness of such models is far from obvious.

Karttunen, H.↗
NASA NTRS1989

Simultaneous axial conduction in the fluid and the pipe wall for forced convective laminar flow with blowing and suction at the wall

Numerical solutions are reported for conjugate heat transfer in a porous pipe having an internal flow with blowing or suction at the inner surface of the pipe and constant heat flux at the outer surface. The effect of the simultaneous axial conduction through the wall and the fluid has been studied for the combined hydrodynamic and thermal entry lengths. The results show that the ratio of the thermal conductivities of the pipe wall to the fluid and the thickness of the pipe wall may become significant factors on the heat transfer when the Peclet number is small, especially for the case when fluid is injected into the pipe. It is also shown that the effect of axial wall conduction for the case of constant heat flux at the outer wall surface can be neglected when the wall thickness is small and the ratio of the conductivities of the wall to the fluid approaches unity.

Faghri, Amir↗
NASA NTRS1991

Effects of dust accumulation and removal on radiators surfaces on Mars

Tests were carried out to assess the impact of wind blown dust accumulation and abrasion on radiator surfaces on Mars. High emittance arc-textured copper and niobium-1 percent-zirconium samples were subjected to basaltic dust laden wind at Martian pressure (1000 Pa) at speeds varying from 19 to 97 m/s in the Martian Surface Wind Tunnel. The effect of accumulated dust was also observed by pre-dusting some of the samples before the test. Radiator degradation was determined by measuring the change in the emittance after dust was deposited and/or removed. The principle mode of degradation was abrasion. Arc textured Nb-1 percent-Zr proved to be more susceptible to degradation than Cu, and pre-dusting appeared to have lessened the abrasion.

Gaier, James R.↗
NASA NTRS1990

Analysis of unsteady compressible viscous layers

The development of an analysis to predict the unsteady compressible flows in blade boundary layers and wakes is presented. The equations that govern the flows in these regions are transformed using an unsteady turbulent generalization of the Levy-Lees transformation. The transformed equations are solved using a finite difference technique in which the solution proceeds by marching in time and in the streamwise direction. Both laminar and turbulent flows are studied, the latter using algebraic turbulence and transition models. Laminar solutions for a flat plate are shown to approach classical asymptotic results for both high and low frequency unsteady motions. Turbulent flat-plate results are in qualitative agreement with previous predictions and measurements. Finally, the numerical technique is also applied to the stator and rotor of a low-speed turbine stage to determine unsteady effects on surface heating. The results compare reasonably well with measured heat transfer data and indicate that nonlinear effects have minimal impact on the mean and unsteady components of the flow.

Power, G. D.↗
NASA NTRS1991

Effects of dust accumulation and removal on radiator surfaces on Mars

Tests were carried out to assess the impact of wind blown dust accumulation and abrasion on radiator surfaces on Mars. High emittance arc-textured copper and niobium-1 percent-zirconium samples were subjected to basaltic dust laden wind at Martian pressure (1000 Pa) at speeds varying from 19 to 97 m/s in the Martian Surface Wind Tunnel. The effect of accumulated dust was also observed by pre-dusting some of the samples before the test. Radiator degradation was determined by measuring the change in the emittance after dust was deposited and/or removed. The principle mode of degradation was abrasion. Arc textured Nb-1 percent-Zr proved to be more susceptible to degradation than Cu, and pre-dusting appeared to have lessened the abrasion.

Gaier, James R.↗
NASA NTRS1994

Combined Contamination and Space Environmental Effects on Solar Cells and Thermal Control Surfaces

For spacecraft in low Earth orbit (LEO), contamination can occur from thruster fuel, sputter contamination products and from products of silicone degradation. This paper describes laboratory testing in which solar cell materials and thermal control surfaces were exposed to simulated spacecraft environmental effects including contamination, atomic oxygen, ultraviolet radiation and thermal cycling. The objective of these experiments was to determine how the interaction of the natural LEO environmental effects with contaminated spacecraft surfaces impacts the performance of these materials. Optical properties of samples were measured and solar cell performance data was obtained. In general, exposure to contamination by thruster fuel resulted in degradation of solar absorptance for fused silica and various thermal control surfaces and degradation of solar cell performance. Fused silica samples which were subsequently exposed to an atomic oxygen/vacuum ultraviolet radiation environment showed reversal of this degradation. These results imply that solar cells and thermal control surfaces which are susceptible to thruster fuel contamination and which also receive atomic oxygen exposure may not undergo significant performance degradation. Materials which were exposed to only vacuum ultraviolet radiation subsequent to contamination showed slight additional degradation in solar absorptance.

Dever, Joyce A.↗
NASA NTRS2005

Trailing Edge Blowing on a Two-Dimensional Six-Percent Thick Elliptical Circulation Control Airfoil Up to Transonic Conditions

A wind tunnel test was conducted in the NASA Langley Transonic Dynamics Tunnel (TDT) on a six percent thick slightly cambered elliptical circulation control airfoil with both upper and lower surface blowing capability. Parametric evaluations of jet slot heights and Coanda surface shapes were conducted at momentum coefficients (Cm) from 0.0 to 0.12. Test data were acquired at Mach numbers of 0.3, 0.5, 0.7, 0.8, and 0.84 at Reynolds numbers per foot of 2.43 x 105 to 1.05 x 106. For a transonic condition, (Mach = 0.8 at alpha = 3 degrees), it was generally found the smaller slot and larger Coanda surface combination was overall more effective than other slot/Coanda surface combinations. Lower surface blowing was not as effective as the upper surface blowing over the same range of momentum coefficients. No appreciable Coanda surface, slot height, or slot blowing position preference was indicated transonically with the dual slot blowing.

Alexander, Michael G.↗
NASA NTRS2015

Capillary Channel Flow (CCF) EU2-02 on the International Space Station (ISS): An Experimental Investigation of Passive Bubble Separations in an Open Capillary Channel

It would be signicantly easier to design fluid systems for spacecraft if the fluid phases behaved similarly to those on earth. In this research an open 15:8 degree wedge-sectioned channel is employed to separate bubbles from a two-phase flow in a microgravity environment. The bubbles appear to rise in the channel and coalesce with the free surface in much the same way as would bubbles in a terrestrial environment, only the combined effects of surface tension, wetting, and conduit geometry replace the role of buoyancy. The host liquid is drawn along the channel by a pump and noncondensible gas bubbles are injected into it near the channel vertex at the channel inlet. Control parameters include bubble volume, bubble frequency, liquid volumetric flow rate, and channel length. The asymmetrically confined bubbles are driven in the cross-flow direction by capillary forces until they at least become inscribed within the section or until they come in contact with the free surface, whereupon they usually coalesce and leave the flow. The merging of bubbles enhances, but does not guarantee, the latter. The experiments are performed aboard the International Space Station as a subset of the Capillary Channel Flow experiments. The flight hardware is commanded remotely and continuously from ground stations during the tests and an extensive array of experiments is conducted identifying numerous bubble flow regimes and regime transitions depending on the ratio and magnitude of the gas and liquid volumetric flow rates. The breadth of the publicly available experiments is conveyed herein primarily by narrative and by regime maps, where transitions are approximated by simple expressions immediately useful for the purposes of design and deeper analysis.

fluid dynamics↗
NASA NTRS1979

Effect of a Pacific sea-surface temperature anomaly on the circulation over North America: A numerical experiment with the GLAS model

A numerical experiment was carried out to determine the effect of sea surface temperature anomalies over the Pacific on the circulation over North America. The sea surface temperature (SST) anomaly pattern chosen for this study was similar to the one observed during January 1977. It is shown that a cold sea surface temperature anomaly over the Pacific produces a strong southward flow over the United States and colder temperature in eastern Canada and the United States, as it was observed during the 1977 winter. The results indicate that the SST anomaly over the Pacific can produce a significant downstream effect over the continental United States.

Shukla, J.↗
DOE OSTI2019

Brush-Modified Materials: Control of Molecular Architecture, Assembly Behavior, Properties and Applications

Recent progress in surface-initiated polymerization enables the deliberate polymer modification of nanoscopic surfaces with high levels of precision. This has given rise to the development of brush particle-based materials (sometimes referred to as ‘hairy nanoparticles’) that are formed by tethering of polymer chains to the surface of nanoparticle-like objects. Brush particles have attracted interest as model systems to understand the effect of surface modification on the structure and interactions in polymer modified colloidal systems (which play a role across fields as diverse as functional coatings, cosmetics, foods or pharmaceuticals) but also as building blocks for the assembly of ‘one-component hybrid materials’ that exhibit unprecedented property combinations, not realizable in classical composite materials. This review presents a summary and analysis of the developments in the field of ‘particle brush materials’. The evolution of synthetic methodologies from the original pioneering work to emerging trends and opportunities in the field of brush synthesis is presented first. Subsequently, the effect of brush architecture on the structure, interaction and assembly of brush particles both with and without a matrix is discussed. Lastly, recent advances in the development of functional hybrid materials with applications in energy, catalysis, sensing and other areas is presented.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Impact of Surface Composition of SrTiO 3 Catalysts for Oxidative Coupling of Methane

Abstract Oxidative coupling of methane (OCM) to C 2 hydrocarbons (C 2 H 6 and C 2 H 4 ) have regained much attention due to the shale gas revolution. Perovskite catalysts have shown promising activity and selectivity to C 2 hydrocarbons. Here, we investigate the effect of surface reconstruction (leading to different surface compositions) of perovskites on the OCM by using SrTiO 3 (STO) as a model catalyst. Different surface densities of Sr (25–96 %) were attained via various treatments of STO. Low energy ion scattering (LEIS) and UV‐Raman results are in good agreement on the surface and subsurface composition of the reconstructed STO. From H 2 ‐TPR, the same H 2 consumption of STO samples allows relating their catalytic performances with surface acid‐base properties (quantified by NH 3 ‐/CO 2 ‐TPD). At 600–800 °C, the surface Sr enrichment was found to enhance CH 4 conversion, C 2 selectivity and the ratio C 2 H 4 /C 2 H 6 up to Sr/(Sr+Ti) of 0.66 and then levels off. Furthermore, the relative concentration of basic sites, base/(base+acid), is found as a better descriptor for STO catalytic performances. This work shows the clear correlation between surface reconstruction, relative basicity/acidity and OCM catalytic performance over perovskite catalysts. The trends here are similar to those for CH 4 combustion over the reconstructed STO in our recent work. Overall, we suggest that tuning surface reconstruction/composition of perovskites can be an effective approach to control CH 4 activation and conversions.

Bai, Lei↗
NASA NTRS2025

Direct Numerical Simulation of Flow Past a Gaussian Bump at a High Reynolds Number

We present the results from a direct numerical simulation of a spanwise-periodic turbulent flow past a Gaussian bump. The problem setup is designed to investigate the interaction of an incoming turbulent boundary layer with the strong favorable and adverse pressure gradients generated by the Gaussian bump as the flow passes over it at a Reynolds number of 340000 based on the bump height, or 4 million based on the bump length. The statistical results from the present simulation are compared against our earlier results at a Reynolds number of 2 million. An internal layer, which forms beneath the strongly accelerated boundary layer over the windward side of the bump, is found to generate its near-wall turbulence stress peaks in closer proximity of the wall in the higher Reynolds-number case. Furthermore, the logarithmic layer of the higher Reynolds-number boundary layer appears more resistant to changes induced by strong acceleration and surface curvature effects over the same region. Despite a nearly identical flow separation point in the two flows, the detached shear layer grows at a faster rate and subsequently reattaches at an earlier point in the higher Reynolds-number flow. The surface pressure and skin-friction distributions over the attached flow region compare well against the corresponding experimental data for both flows. However, some differences appear in the separated flow region, which are attributed to the three-dimensionality of the experimental model setup that is not included in the simulation owing to the spanwise periodic assumption. Comparisons with the stereoscopic particle image velocimetry measurements on the central plane of the experimental model over the windward side of the bump show reasonable overall agreement in the mean velocity components, but the turbulence stress components do not agree well at some streamwise locations. Comparisons over the leeward side of the bump show that the mean separated shear layer in the simulation is tilted significantly more toward the wall than the experimental shear layer on the central plane. This mismatch in the mean shear layer orientation is due to the experimental model three-dimensionality and tunnel end-wall effects, which are not modeled in the present spanwise-periodic simulation.

Favorable and Adverse Pressure Gradients↗
NASA NTRS1972

Problems affecting the fidelity of pressure measuring instruments for planetary probes

Determination is made of the nature and magnitude of surface-related effects that cause errors in pressure measuring instruments, with special reference being made to instruments intended for use in planetary probes. The interaction of gases with clean surfaces of metals likely to be used as gage construction materials was studied. Special emphasis was placed on the adsorption, chemical reaction, and electron-induced desorption processes. The results indicated that all metals tested were subject to surface processes which would degrade gage fidelity. It was also found, however, that the formation of inert adsorbed layers on these metal surfaces, such as carbon on platinum, greatly reduced or eliminated these effects. This process, combined with a system design which avoids contact between reactive gases and hot filaments, appears to offer the most promising solution to the gage fidelity problem.

Hudson, J. B.↗
DOE OSTI2025

Influence of AA6061 surface preparation on the resistance to surface degradation of thermally grown boehmite films

Understanding substrate–coating interactions is crucial for designing durable, corrosion-resistant systems. This study investigates the effects of surface treatments— polishing, acid etching, and alkaline etching—on AA6061 aluminum alloy and its thermally grown boehmite coatings. Surface treatments were found to significantly alter boehmite film properties by modifying the alloy’s surface composition. X-ray photoelectron spectroscopy revealed a 10% alumina drop after acid etching alongside chemisorbed species formation in wet treatments. Structural analysis, including grazing incidence X-ray diffraction and TEM, showed α-Al 2 O 3 formation on polished surfaces, improving wear resistance but inducing cathodic E corr shifts, pointing to higher corrosion susceptibility. In contrast, acid and alkaline etching produced anodic E corr shifts with stable, pit-free films observed via potentiodynamic scans. Electrochemical impedance spectroscopy highlighted reduced oxide resistance with extended boehmite growth. The findings emphasize the role of surface pre-treatments and boehmite optimization in balancing durability and corrosion resistance for AA6061 substrates.

AA6061↗