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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 505 records · Page 28
All sourcesNASA NTRSDOE OSTI
NASA NTRS2020

Effective Crewed Surface Science near the Lunar South Pole: Some Illumination Considerations

Exploration near the lunar South Pole has substantial scientific promise for expanding our understanding of the Moon beyond what has been accomplished by Apollo and other lunar missions. An obvious difference from the Apollo experience is that the polar location for Artemis will guarantee the Sun is going to be low above the horizon. A great deal of excellent work has been, and is being, done on the availability of light (“yes/no”) for exploration purposes [e.g., 1-4]. However, we raise the additional consideration of the qualitative effects of low solar elevation on crew traverses, crew observations, and other science measurements [see also 5, though ground rules of that study presumed higher Sun]. We emphasize that our view is that these issues are unlikely to be mission objective-threatening, particularly if adequately considered in advance.

C. I. Fassett↗
DOE OSTI2019

Aerosol Direct Radiative and Cloud Adjustment Effects on Surface Climate over Eastern China: Analyses of WRF Model Simulations

The WRF-simulated changes in clouds and climate due to the increased anthropogenic aerosols for the summers of 2002–08 (vs the 1970s) over eastern China were used to offline calculate the radiative forcings associated with aerosol–radiation (AR) and aerosol–cloud–radiation (ACR) interactions, which subsequently facilitated the interpretation of surface temperature changes. During this period, the increases of aerosol optical depth (ΔAOD) averaged over eastern China range from 0.18 in 2004 to 0.26 in 2007 as compared to corresponding cases in the 1970s, and the multiyear means (standard deviations) of AR and ACR forcings at the surface are −6.7 (0.58) and −3.5 (0.63) W m −2 , respectively, indicating the importance of cloud changes in affecting both the aerosol climate forcing and its interannual variation. The simulated mean surface cooling is 0.35°C, dominated by AR and ACR with a positive (cooling) feedback associated with changes in meteorology (~10%), and two negative (warming) feedbacks associated with decreases in latent (~70%) and sensible (~20%) heat fluxes. More detailed spatial characteristics were analyzed using ensemble simulations for the year 2008. Three regions—Jing-Jin-Ji (ΔAOD ~ 0.63), Sichuan basin (ΔAOD ~ 0.31), and middle Yangtze River valley (ΔAOD ~ 0.26)—at different climate regimes were selected to investigate the relative roles of AR and ACR. While the AR forcing is closely related to ΔAOD values, the ACR forcing presents different regional characteristics owing to cloud changes. In addition, the surface heat flux feedbacks are also different between regions. The study thus illustrates that ACR forcing is useful as a diagnostic parameter to unravel the complexity of climate change to aerosol forcing over eastern China.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2021

Bounds on the Rate-Dependent Plastic Flow of Tantalum up to 75 GPa

In this study we report on the continued development of thermodynamics-based analysis of shock waves propagation with the objective of extracting information related to materials strength at high strain rates and pressures. Building on previous results reported for peak stresses of 10 GPa and 25 GPa, we present a series of three-step gas-gun shock experiments designed to explore the pressure and strain rate dependence of plastic flow in polycrystalline tantalum. These experiments at nominal peak stresses of 50 GPa and 75 GPa show the irreversible deformation before pullback to be almost entirely confined to the shock loading, with negligible plastic relaxation on the post-shock plateau. We also add a reverse-ballistics shot at 25 GPa, which was designed to reveal the pullback response with negligible interference from free-surface effects. General thermodynamic considerations allow us to place bounds on the plastic behavior even for parts of the curve that change far too rapidly for the velocimetric time resolution of (conservatively) ~ 5 ns. To analyze the data, we found it necessary to substantially improve the interpolation/extrapolation scheme in order to improve its robustness, flexibility and range of applicability. We describe the new scheme based on splines, as well as an extension of free-surface corrections to the post-shock rarefaction waves. Reanalysis with the new scheme produces results essentially within the error bars previously reported, showing that the known systematic errors associated with free-surface effects are relatively inconsequential for determining thermodynamic paths.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2020

Covalent Surface Modification Effects on Single‐Walled Carbon Nanotubes for Targeted Sensing and Optical Imaging

Abstract Optical nanoscale technologies often implement covalent or noncovalent strategies for the modification of nanoparticles, whereby both functionalizations are leveraged for multimodal applications but can affect the intrinsic fluorescence of nanoparticles. Specifically, single‐walled carbon nanotubes (SWCNTs) can enable real‐time imaging and cellular delivery; however, the introduction of covalent SWCNT sidewall functionalizations often attenuates SWCNT fluorescence. Recent advances in SWCNT covalent functionalization chemistries preserve the SWCNT's pristine graphitic lattice and intrinsic fluorescence, and here, such covalently functionalized SWCNTs maintain intrinsic fluorescence‐based molecular recognition of neurotransmitter and protein analytes. The covalently modified SWCNT nanosensor preserves its fluorescence response towards its analyte for certain nanosensors, presumably dependent on the intermolecular interactions between SWCNTs or the steric hindrance introduced by the covalent functionalization that hinders noncovalent interactions with the SWCNT surface. These SWCNT nanosensors are further functionalized via their covalent handles with a targeting ligand, biotin, to self‐assemble on passivated microscopy slides, and these dual‐functionalized SWCNT materials are explored for future use in multiplexed sensing and imaging applications.

Chio, Linda↗
NASA NTRS1974

Effects of surface roughness on the aerodynamic characteristics of the modified 089 B shuttle orbiter at Mach 6 (LA15)

A one hundredth scale model of the modified 089B shuttle orbiter was tested in the Langley 20-Inch Mach 6 tunnel. Force and moment, surface pressure and oilflow data were obtained on one model, and phase-change coating data were obtained on another. The pressure tests were conducted first; the tubes were clipped near the base of the model and then the force and moment and oil flow tests conducted. Angles of attack for the tests were from 20 deg to 35 deg and are commensurate with the range of flight values from entry down to Mach 5. The design flight Reynolds number at Mach 6, based on model length, was 15 million, which could not be obtained in the tunnel; therefore, the tests were conducted at the highest and lowest values for this model in the tunnel, 9.4 million and 4.0 million, respectively, to indicate Reynolds number effects. Two control deflection combinations, representative of the bank and pitch control limits of the design flight trajectory, were used.

Ashby, G. C., Jr.↗
DOE OSTI2017

Effect of Surface Roughness on Wind Turbine Performance

Wind farm operators observe production deficits as machines age. Quantifying deterioration on individual components is difficult, but one potential explanation is accumulation of blade surface roughness. Historically, wind turbine airfoils were designed for lift to be insensitive to roughness by simulating roughness with trip strips. However, roughness was still shown to negatively affect performance. Furthermore, experiments illustrated distributed roughness is not properly simulated by trip strips. To understand how real-world roughness affects performance, field measurements of turbine-blade roughness were made and simulated on a NACA 63 3 -418 airfoil in a wind tunnel. Insect roughness and paint chips were characterized and recreated as distributed roughness and a forward-facing step. Distributed roughness was tested in three heights and five density configurations. The model chord Reynolds number was varied between 0.8 to 4.8 x 10 6 . Measurements of lift, drag, pitching moment, and boundary-layer transition were completed. Results indicate minimal effect from paint-chip roughness. As distributed roughness height and density increase, lift-curve slope, maximum lift, and lift-to-drag ratio decrease. As Reynolds number increases, bypass transition occurs earlier. The critical roughness Reynolds number varies between 178 to 318, within the historical range. Little sensitivity to pressure gradient is observed. At a chord Reynolds number of 3.2 x 10 6 , the maximum lift-to-drag ratio decreases 40% for 140 m roughness, corresponding to a 2.3% loss in annual energy production. Simulated performance loss compares well to measured performance loss on an in-service wind turbine.

17 WIND ENERGY↗
NASA NTRS2013

The Effects of Surfaces on the Aerodynamics and Acoustics of Jet Flows

Aircraft noise mitigation is an ongoing challenge for the aeronautics research community. In response to this challenge, low-noise aircraft concepts have been developed that exhibit situations where the jet exhaust interacts with an airframe surface. Jet flows interacting with nearby surfaces manifest a complex behavior in which acoustic and aerodynamic characteristics are altered. In this paper, the variation of the aerodynamics, acoustic source, and far-field acoustic intensity are examined as a large at plate is positioned relative to the nozzle exit. Steady Reynolds-Averaged Navier-Stokes solutions are examined to study the aerodynamic changes in the field-variables and turbulence statistics. The mixing noise model of Tam and Auriault is used to predict the noise produced by the jet. To validate both the aerodynamic and the noise prediction models, results are compared with Particle Image Velocimetry (PIV) and free-field acoustic data respectively. The variation of the aerodynamic quantities and noise source are examined by comparing predictions from various jet and at plate configurations with an isolated jet. To quantify the propulsion airframe aeroacoustic installation effects on the aerodynamic noise source, a non-dimensional number is formed that contains the flow-conditions and airframe installation parameters.

Smith, Matthew J.↗
NASA NTRS1986

Surface film effects on drop tube undercooling studies

The effects of various gaseous atmospheric constituents on drop-tube solidified samples of elemental metals were examined from a microstructural standpoint. All specimens were prepared from the purest available elements, so effects of impurities should not account for the observed effects. The drop-tube gas has a definite effect on the sample microstructure. Most dramatically, the sample cooling rate is effected. Some samples receive sufficient cooling to solidify in free fall while others do not, splating at the end of the drop tube in the sample catcher. Gases are selectively absorbed into the sample. Upon solidification gas can become less soluble and as a result forms voids within the sample. The general oxidation/reduction characteristics of the gas also affect sample microstructures. In general, under the more favorable experimental conditions including reducing atmospheric conditions and superheatings, examination of sample microstructures indicates that nucleation has been suppressed. This is indicated by underlying uniform dendrite spacings throughout the sample and with a single dendrite orientation through most of the sample. The samples were annealed yielding a few large grains and single or bi-crystal samples were commonly formed. This was especially true of samples that were inadvertently greatly superheated. This is in contrast with results from a previous study in which surface oxides were stable and contained numerous sites of nucleation. The number of nucleation events depends upon the surface state of the specimen as determined by the atmosphere and is consistent with theoretical expectations based upon the thermodynamic stability of surface oxide films. Oxide-free specimens are characterized by shiny surfaces, with no observable features under the scanning electron microscope at 5000X.

Ethridge, E. C.↗
DOE OSTI2023

Effect of Surface Temperature on the Distribution and Reactivity of Rh Active Sites for CO Oxidation

Single–atom catalysts are a fast–emerging area in which late–transition metal atoms are supported on oxides, metals, and carbonaceous supports. They show great promise for selective chemical reactions due to their well–defined active sites, and significantly reduce precious metal loading. However, oxide–supported single–atom catalysts have drawbacks such as deactivation due to sintering, and there are on–going debates about the exact nature of the active sites. Herein we report a model system where the surface temperature during Rh deposition on a copper oxide support dictates the Rh size distribution. Here our temperature–programmed desorption experiments reveal that Rh clusters perform CO oxidation at lower temperature than single atoms, and isotopic labelling demonstrates differences in the mechanism in that the C–O bond is broken and reformed on clusters, as opposed to a pure Mars van Krevelen mechanism for CO oxidation at the single–atom Rh sites. We further examine the cluster size distributions with scanning tunneling microscopy and X–ray photoelectron spectroscopy which confirm the presence of both clusters and single atoms for the lower temperature deposition and only single atoms for the higher temperature deposition. Together, these results provide a fundamental understanding of the differences in the CO oxidation mechanism on Rh atoms and clusters.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Exploring the Effect of Surface Functionality on the Self-Assembly of Polyoxopalladate Macroions

The solution behavior of the two polyoxo-13-palladates(II) ([Pd(II) 13 As(V) 8 O34 (OH)6 ](8-) and [Pd(II) 13 (As(V) Ph)8 O32 ](6-) ) was studied in detail. We discovered that the countercation-mediated attraction is the driving force for their self-assembly into larger architectures. However, the presence of phenyl groups in the periphery of [Pd(II) 13 (As(V) Ph)8 O32 ](6-) results in an enhanced attraction among these polyanions through hydrophobic interactions, which leads to completely different trends of assembly size for these two very similar clusters when decreasing solvent polarity. An increase of assembly size with increasing solvent polarity was observed for [Pd(II) 13 (As(V) Ph)8 O32 ](6-) , whereas for [Pd(II) 13 As (V) 8 O34 (OH)6 ](8-) it was the opposite, due to the absence of hydrophobic interactions.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2019

Effects of Surface Modifications of Kraft Wood Pulp Cellulose Fibres on Improving the Mechanical Properties of Cellulose Fibre/Latex Composites

In this work, three composites with different contents (5, 10, and 15% w/w) of kraft pulp fibre were produced as reinforcing elements for natural latex matrix and the mechanical properties were evaluated. In order to improve the interfacial adhesion between the matrix and the reinforcing element, chemical modifications were carried out on the surface of the fibres using octanoyl and benzoyl chlorides as modifying agents. The extension of chemical modification of the fibres was visualized by the presence of absorption bands in the spectroscopy analyzes of the modified fibre in relation to the crude fibre (ester carbonyl 1700–1740 cm{sup −1}); in addition, the hydroxyl band was preserved, which indicates a modification of surface character. The modified fibres became more hydrophobic due to the decrease in surface energy and the change in the dispersive and polar components. An increase in the storage modulus was observed for the composites with surface-modified fibres, which agrees with the improved dispersion between the surface-modified fibres and the matrix verified by means of scanning electron microscopy images. The incorporation of fibres did not cause changes in the thermal properties of the composites.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Effect of Surface Self-Nanocrystallization on Diffusion Bonding Between a Titanium Alloy and a TiAl-Based Alloy

A self-nanocrystallization layer was prepared on the surface of a Ti alloy sample via shot peening to investigate its influence on the follow-up diffusion bonding between a titanium alloy and a TiAl-based alloy. The experiment results show that surface self-nanocrystallization treatment can accelerate the interface reaction between a Ti alloy and a TiAl alloy, lowering the bonding temperature of the sound joints by more than 50 K. Moreover, the thickness of the interface reaction layer plays an important role in the interfacial bonding strength. In this work, the maximum shear strength of the joint appears to have a thickness of about 1.8 μm. As a consequence, it is found that surface self-nanocrystallization treatment is helpful for optimizing the diffusion bonding process.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2019

The Effect of Surface Condition on Wetting of HASTELLOY{sup ®} X by Brazing Filler Metal of Ni-Pd-Cr-B-Si System

The paper presents the results of wettability tests by a sessile drop method coupled with residual gas analysis for the HASTELLOY{sup ®} X substrates contact heated with brazing filler metal of Palnicro 36M. The contact angles formed between the substrate and the molten brazing filler metal were recorded by high-speed high-resolution CCD camera using two different heating procedures: (1) fast continuous heating to a temperature of 960 °C; (2) isothermal heating at a temperature of 995 °C for 10 min after step heating to the test temperature. In this study, the reference sample was HASTELLOY{sup ®} X in a delivery state (D1). The base material with a different surface finish was also tested: after polishing (P1), after polishing and oxidation at a temperature of 600 °C for 1 h in the air (U1). The tests confirmed very good wetting properties of Palnicro 36M on HASTELLOY{sup ®} X, independently on its surface finish and the heating procedure used in this study, i.e., after 10 min at 995 °C, the final contact angle values were θ{sub f} = 7.6 ± 0.1°, 6.03 ± 0.07° and 6.2 ± 1.0° for D1, P1 and U1, respectively. However, oxidation of HASTELLOY{sup ®} X surface affects the wetting kinetics and spreading of molten Palnicro 36M on BM substrates by: (1) increasing the initial contact angle values (θ{sub 0} = 51 ± 4°, 65 ± 13° and 83 ± 2° for D1, P1 and U1, respectively), (2) delaying the wetting process and (3) reducing the spreading area since after wettability tests at 960 °C, the largest area covered with solidified Palnicro 36M drop was noted for D1 (92 mm{sup 2}) while the smallest one for U1 (52 mm{sup 2}).

36 MATERIALS SCIENCE↗
DOE OSTI2022

Efficient Pd on carbon catalyst for ammonium formate dehydrogenation: Effect of surface oxygen functional groups

Formate solution is one of a kind promising liquid organic hydrogen carrier but suffers from kinetic challenges. This study investigates the kinetics of the surfacefunctionalized Pd on carbon catalysts for formate dehydrogenation and the impact of O-functional groups. Here, the fraction of the distinguished O-functional groups was modulated by the different concentrated HNO 3 solutions treatment or by H 2 reduction. This study shows that the O-functional groups play critical roles in dispersing Pd nanoparticles and decreasing the activation energy for dehydrogenation. Density functional theory (DFT) calculation reveals that most O-functional groups enhance formate adsorption on the Pd active site. However, the existence of C=O groups consumes reducing agents and hinders the formation of metallic Pd. The electron transfer from Pd to oxygen functional groups is unfavorable to dehydrogenation. The as-prepared Pd5/re-ACA (reduced activated carbon washed by acid) exhibited significant activity with a higher turnover frequency of 13,511 h -1 than commercial Pd/C.

54 ENVIRONMENTAL SCIENCES↗