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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 37 records · Page 2
All sourcesNASA NTRSDOE OSTI
NASA NTRS1974

Thermophysical properties of lunar media. II - Heat transfer within the lunar surface layer

Heat transfer within the lunar surface layer depends on several thermophysical properties of the lunar regolith, including the thermal conductivity, the specific heat, the thermal diffusivity, and the thermal parameter. Results of property measurements on simulated lunar materials are presented where appropriate as well as measurements made on the actual samples themselves. The variation of temperature on the moon with depth is considered, taking into account various times of the lunar day. The daily variation in temperature drops to about 1 deg at a depth of only 0.172 meters. The steady temperature on the moon below this depth is 225 K.

Cremers, C. J.↗
DOE OSTI2023

Evidence of Mixed Scaling for Mean Profile Similarity in the Stable Atmospheric Surface Layer

A new mixed scaling parameter Z = z/(Lh)1/2 is proposed for similarity in the stable atmospheric surface layer, where z is the height, L is the Obukhov length, and h is the boundary layer depth. In comparison with the parameter ζ = z/L from Monin–Obukhov similarity theory (MOST), the new parameter Z leads to improved mean profile similarity for wind speed and air temperature in large-eddy simulations. It also yields the same linear similarity relation for CASES-99 field measurements, including in the strongly stable (but still turbulent) regime where large deviations from MOST are observed. Results further suggest that similarity for turbulent energy dissipation rate depends on both Z and ζ. The proposed mixed scaling of Z and relevance of h can be explained by physical arguments related to the limit of z-less stratification that is reached asymptotically above the surface layer. The presented evidence and fitted similarity relations are promising, but the results and arguments are limited to a small sample of idealized stationary stable boundary layers. Here, corroboration is needed from independent datasets and analyses, including for complex and transient conditions not tested here.

54 ENVIRONMENTAL SCIENCES↗
NASA NTRS1987

Airborne measurements of surface layer turbulence over the ocean during cold air outbreaks

The spectral characteristics of surface layer turbulence for the near-shore cloud street regions over the Atlantic Ocean were examined using 50-m level data of airborne measurements of atmospheric turbulence spectra above the western Atlantic Ocean during cold air outbreaks. The present study, performed for the Mesoscale Air-Sea Exchange (MASEX) experiment, extends and completes the preliminary analyses of Chou and Yeh (1987). In the inertial subrange, a near 4/3 ratio was observed between velocity spectra normal to and those along the aircraft heading. A comparison of the turbulent kinetic energy budgets with those of Wyngaard and Cote (1971) and Caughey and Wyngaard (1979) data indicates that the turbulent kinetic energy in the surface layer is dissipated less in the MASEX data than in data obtained by the previous groups.

Chou, Shu-Shien↗
NASA NTRS1984

Determination of monthly mean humidity in the atmospheric surface layer over oceans from satellite data

A simple statistical technique is described to determine monthly mean marine surface-layer humidity, which is essential in the specification of surface latent heat flux, from total water vapor in the atmospheric column measured by space-borne sensors. Good correlation between the two quantities was found in examining the humidity soundings from radiosonde reports of mid-ocean island stations and weather ships. The relation agrees with that obtained from satellite (Seasat) data and ship reports averaged over 2 deg areas and a 92-day period in the North Atlantic and in the tropical Pacific. The results demonstrate that, by using a local regression in the tropical Pacific, total water vapor can be used to determine monthly mean surface layer humidity to an accuracy of 0.4 g/kg. With a global regression, determination to an accuracy of 0.8 g/kg is possible. These accuracies correspond to approximately 10 to 20 W/sq m in the determination of latent heat flux with the bulk parameterization method, provided that other required parameters are known.

Liu, W. T.↗
NASA NTRS1976

Laws of effluent dispersion in the steady-state atmospheric surface layer in stable and unstable conditions

The two-dimensional diffusion equation has been solved by an integral method to obtain the distribution of ground-level concentration of an inert effluent emitted from a semi-infinite area source in a steady-state and horizontally homogeneous atmospheric surface layer. Mean wind velocity and eddy diffusivity profiles derived from empirically determined flux-profile relations of Businger et al. (1971) for stable and unstable surface layers were used. It is found that concentration as a function of downwind distance can be described by a simple formula over distances of practical interest in surface layer dispersion. Corresponding results for a cross-wind infinite line source are obtained by simple differentiation. The concentration distribution is completely determined by the friction velocity, the Monin-Obukhov length, the roughness length, and the effluent source strength. The generalization of the integral method needed to obtain accurate solutions of the diffusion equation with the given wind velocity and diffusivity profiles is discussed in an appendix.

Lebedeff, S. A.↗
NASA NTRS1992

The Martian surface layer

The global characteristics of the Martian surface layer are discussed on the basis of thermal, albedo, color, and radar data for the region between approximately 60 deg S and 60 deg N. Thermal data reveal the presence of large low- and high-inertia regions of the northern hemisphere, with much of the south covered by material of moderate inertia. There is a strong anticorrelation between inertia and albedo, a correlation between inertia and rock abundance, and, over much of the planet, a correlation of radar-derived density with inertia. Viking Orbiter color data indicate the presence of three major surface materials: low-inertia, bright-red material that is presumably dust; high-inertia, dark-grey material interpreted to be lithic material mixed with palagonitelike dust; and moderate-inertia, dark-red material that is rough at subpixel scales and interpreted to be indurated. Observations from the Viking landing sites show rocks, fines of varying cohesion and crusts. These sites have indications of aeolian erosion and deposition in the recent past.

Christensen, Philip R.↗
DOE OSTI2023

Improving Oxygen Reduction Performance of Surface-Layer-Controlled Pt–Ni Nano-Octahedra via Gaseous Etching

This study demonstrates an atomic composition manipulation on Pt–Ni nano-octahedra to enhance their electrocatalytic performance. By selectively extracting Ni atoms from the {111} facets of the Pt–Ni nano-octahedra using gaseous carbon monoxide at an elevated temperature, a Pt-rich shell is formed, resulting in an ~2 atomic layer Pt-skin. The surface-engineered octahedral nanocatalyst exhibits a significant enhancement in both mass activity (~1.8-fold) and specific activity (~2.2-fold) toward the oxygen reduction reaction compared with its unmodified counterpart. After 20,000 potential cycles of durability tests, the surface-etched Pt–Ni nano-octahedral sample shows a mass activity of 1.50 A/mg Pt , exceeding the initial mass activity of the unetched counterpart (1.40 A/mg Pt ) and outperforming the benchmark Pt/C (0.18 A/mg Pt ) by a factor of 8. DFT calculations predict this improvement with the Pt surface layers and support these experimental observations. Therefore, this surface-engineering protocol provides a promising strategy for developing novel electrocatalysts with improved catalytic features.

36 MATERIALS SCIENCE↗
NASA NTRS1982

Magnetic field-related heating instabilities in the surface layers of the sun and stars

The stability of a magnetized low-density plasma to current-driven filamentation instabilities is investigated and the results are applied to the surface layers of stars. Unlike previous studies, the initial (i.e., precoronal) state of the stellar surface atmosphere is taken to be a low-density, optically thin magnetized plasma in radiative equilibrium. The linear analysis shows that the surface layers of main-sequence stars (including the sun) which are threaded by magnetic fields are unstable; the instabilities considered lead to structuring perpendicular to the ambient magnetic fields. These results suggest that relatively modest surface motions, in conjunction with the presence of magnetic fields, suffice to account for the presence of inhomogeneous chromospheric and coronal plasma overlying a star's surface.

Ferrari, A.↗
DOE OSTI2020

Assessing the sensitivity of land-atmosphere coupling strength to boundary and surface layer parameters in the WRF model over Amazon

Modeling tools can be used to diagnose regional land-atmosphere (L-A) coupling strength in the absence of sufficient observations, but subject to uncertainties associated with parameters in model physical parameterizations. Different sensitivity analysis (SA) approaches may lead to different conclusions about the underlying sensitivities. In this study, we quantify simulation uncertainties related to parameter perturbations, and use different approaches to conduct parameter SA on the WRF model pertaining to L-A coupling strength for simulations over the Amazon region. A total of twenty parameters from the Yonsei University (YSU) planetary boundary layer (PBL) and the revised MM5 surface layer (SL) schemes were selected in this analysis. Three different SA methods, the Morris One-at-A-Time (MOAT) method, the Multivariate Adaptive Regression Splines (MARS) method, and the Sobol’ method, were employed to analyze seven WRF-simulated variables and five L-A coupling metrics. Results show that 1) parameter perturbations cause large simulation uncertainties which are comparable to those in the observations; 2) three different SA methods give consistent L-A coupling strength outcomes; 3) six out of the twenty parameters contribute 80%–95% of the total variance in the metrics analyzed, and first-order effects dominate over interaction effects; 4) the twelve variables/metrics of interest show similar sensitivity patterns to the selected parameters, which is consistent across all the methods used. Physical mechanisms for how the sensitive parameters act in determining the L-A coupling strength and associated variables also are illustrated. Our results will help quantifying L-A coupling strength and establishing a basis for parameter calibration over the Amazon region.

Wang, Chen↗
NASA NTRS1992

The effect of a non-volatile dust mantle on the energy balance of cometary surface layers

It is likely that large parts of a cometary surface layer consist of porous ices, which are covered by a thin layer of non-volatile debris, whose structure is also fluffy and porous. In this paper the results of model calculations are presented. The calculations show the effect of ice and dust pore sizes and of the dust mantle thickness upon the thermal behavior of such a dust-ice system, when it is irradiated by the sun. In particular, it is found that the average pore size of the ice and the dust material has a large influence both on the dust surface temperature and on the temperature at the dust-ice interface.

Koemle, Norbert I.↗
NASA NTRS1979

Results and interpretation of measurements of the light flux in the near-surface layer of the Venusian atmosphere

The characteristics of the field of radiation in the near surface layer of the atmosphere and on the surface of Venus are reported. Optical measurements made during the landing of the descent vehicles are described. The relief of the surface and the amount of dust on it are examined. The spectral relationship of the albedo of the soil and the light flux incident on the surface is discussed.

Golovin, Y. M.↗
DOE OSTI2020

Effect of a Cr-rich surface layer on D retention in various RAFM steels

In this work, deuterium (D) retention is compared between various reduced-activation ferritic/martensitic steels, including CLF-1, Eurofer, F82H, and Rusfer, exposed to pure D plasma (ion flux ~1.5–2 × 10 21 m -2 s -1 , fluence, ϕ D , ~1 × 10 25 m -2 , sample temperature ~373 K, and incident ion energy ~100 eV). It is found that there is a large difference (up to ~30x) in the D retention between CLF-1 and F82H even with the same plasma exposure condition and similar nominal composition. The ϕ D dependence of the D retention exhibits a peculiar, counterintuitive feature: the D retention decreases with an increase in ϕ D from 2 × 10 23 m -2 to 1 × 10 25 m -2 . Surface analyses reveal that a Cr-rich surface layer is formed during outgassing at 773 K for 1 h before plasma exposure, and that there exists a clear correlation between the D retention and the Cr content in the surface layer.

36 MATERIALS SCIENCE↗