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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 NTRS1981

Comparison of experimental and theoretical turbulence reduction characteristics for screens, honeycomb, and honeycomb-screen combinations

Turbulence reduction research using screens, honeycomb, and combinations thereof was conducted in a half-scale model of a portion of the Langley 8-foot transonic pressure tunnel. It was found that screens alone reduce axial turbulence more than lateral turbulence; whereas, honeycomb alone reduces laterial turbulence more than axial turbulence. Because of this difference, the physical mechanism for decreasing turbulence for screens and honeycomb must be completely different. It is concluded that honeycomb with a downstream screen is an excellent combination for reducing turbulences.

Scheiman, J.↗
NASA NTRS1980

A comparison of experimental and theoretical turbulence reduction from screens, honeycomb and honeycomb-screen combinations

A 1/2-scale model of a portion of the NASA Langley 8-foot transonic pressure tunnel was used to conduct some turbulence reduction research. The experimental results are correlated with various theories. Screens alone reduce axial turbulence more than the lateral turbulence; whereas, honeycomb alone reduce lateral turbulence more than axial turbulence. Because of this difference, the physical mechanism for decreasing turbulence for screens and honeycomb must be completely different. Honeycomb with a downstream screen is an excellent combination for reducing turbulence.

Scheiman, J.↗
DOE OSTI2022

DISCOVR strain pipeline screening – Part II: Winter and summer season areal productivities and biomass compositional shifts in climate-simulation photobioreactor cultures

Assessing the seasonal biomass productivity and compositional shift dynamics under simulated outdoor culture conditions of the top 22 algae strains selected during Tier I flask screening is an important step in the further prioritization of strains with regard to outdoor pond cultivation. These top 22 strains were subjected to Tier II testing in the PNNL Laboratory Environmental Algae Pond Simulator (LEAPS) photobioreactors, simulating light and temperature conditions of 20 cm deep outdoor ponds during the Arizona winter and summer season. All strains were grown in two consecutive nutrient-replete batch culture experiments at their particular optimal medium salinity to quantify their respective seasonal linear-phase areal biomass productivities. To determine biomass compositional shifts in response to nutrient-depletion, the LEAPS cultures were allowed to enter a 9-day nutrient depletion phase at the end of the second batch run. The following strains were evaluated in winter-season climate-simulated cultures and are listed in the order from highest (7.9 g m -2 day -1 ) to lowest (2.3 g m -2 day -1 ) areal N-replete biomass productivity: Monoraphidium minutum 26B-AM, Tetraselmis striata LANL1001, Chlorella vulgaris LRB AZ-1201, Micractinium reisseri NREL14-F2, Monoraphidium sp. MONOR1, Chlorella vulgaris NREL4-C12, Scenedesmus obliquus UTEX393, Scenedesmus acutus LRB-AP-0401, Nannochloropsis oceanica CCAP849/10, and Stichococcus minutus CCALA727. The following strains were evaluated in summer-season climate-simulated cultures and are listed in the order from highest (31.8 g m -2 day -1 ) to lowest (14.2 g m -2 day -1 ) areal N-replete biomass productivity: Picochlorum renovo NREL39-A8, Scenedesmus obliquus UTEX393, Porphyridium cruentum CCMP675, Picochlorum celeri TG2-WT-CSM/EMRE, Chlorella sorokiniana DOE1116, Stichococcus minor CCMP819, Picochlorum oklahomensis CCMP2329, Chlorella sorokiniana DOE1412 (UTEXB3016), Scenedesmus rubescens NREL46B-D3, Picochlorum soloecismus DOE101, Tetraselmis striata LANL1001, Scenedesmus obliquus DOE 0152.z, and Agmenellum quadruplicatum UTEX2268. All LEAPS cultures experienced a significant reduction in areal biomass productivity in response to nutrient-depletion, from 7-16% in the winter season simulation and up to 1-60% in the summer season simulation. Finally, for 10 of the strains tested, the carbohydrate content more than doubled upon nutrient depletion, and for 9 strains, the lipid content increased by over 50% of the initial content.

09 BIOMASS FUELS↗
DOE OSTI2021

Dielectric Screening Modulates Semiconductor Nanoplatelet Excitons

The influence of external dielectric environments is well understood for 2D semiconductor materials but overlooked for colloidally grown II–VI nanoplatelets (NPLs). In this work, we synthesize MX (M = Cd, Hg; X = Se, Te) NPLs of varying thicknesses and apply the Elliott model to extract exciton binding energies—reporting values in good agreement with prior methods and extending to less studied cadmium telluride and mercury chalcogenide NPLs. Here, we find that the exciton binding energy is modulated both by the relative effect of internal vs external dielectric and by the thickness of the semiconductor material. An analytical model shows dielectric screening increases the exciton binding energy relative to the bulk by distorting the Coulombic potential across the NPL surface. We further confirm this effect by decreasing and recovering the exciton binding energy of HgTe NPLs through washing in polarizable solvents. Our results illustrate NPLs are colloidal analogues of van der Waals 2D semiconductors and point to surface modification as an approach to control photophysics and device properties.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2020

Parallelized Screening of Characterized and DFT-Modeled Bimetallic Colloidal Cocatalysts for Photocatalytic Hydrogen Evolution

Using a newly designed and developed parallelized photoreactor and colorimetric detection method, a large sampling of bimetallic co-catalysts (Pd/Sn, Pd/Mo, Pd/Ru, Pd/Pb, Pd/Ni, Ni/Sn, Mo/Sn and Pt/Sn) for photocatalytic water reduction have been tested in this work. Of these co-catalysts, the combination of palladium and tin showed the highest synergistic behavior and peak hydrogen gas production at a low relative fraction of palladium. The resulting Pd/Sn bimetallic co-catalysts were characterized using high-angle annular dark-field (HAADF) and scanning transmission electron microscopy energy dispersive X-ray spectroscopy (STEM-EDS), and specifically, investigation of the palladium/tin mixture indicated that palladium and tin elements reside within the same particle. The experimental catalytic activity for the palladium/tin mixture was compared to density functional theory-derived energy values associated with the adsorption of hydrogen onto a surface. This comparison demonstrated that the typical peak found in electrochemical Sabatier volcano plots at ΔG H* = ~0 eV was replicated in the experimental photocatalytic system with a peak activity observed at ΔG H* = -0.036 eV. Computational confirmation of the results expressed here demonstrates the efficacy of colorimetric detection of hydrogen in parallel and presents a model for increasingly rapid catalyst screening.

08 HYDROGEN↗
DOE OSTI2017

Conservation laws, vertex corrections, and screening in Raman spectroscopy

We present a microscopic theory for the Raman response of a clean multiband superconductor, with emphasis on the effects of vertex corrections and long-range Coulomb interaction. The measured Raman intensity, R⁡(Ω), is proportional to the imaginary part of the fully renormalized particle-hole correlator with Raman form factors γ⁡( ⃗ k). In a BCS superconductor, a bare Raman bubble is nonzero for any γ⁡( ⃗ k) and diverges at Ω = 2⁢Δ max , where Δ max is the largest gap along the Fermi surface. However, for γ( ⃗ k) = constant, the full R⁡(Ω) is expected to vanish due to particle number conservation. It was sometimes stated that this vanishing is due to the singular screening by long-range Coulomb interaction. In our general approach, we show diagrammatically that this vanishing actually holds due to vertex corrections from the same short-range interaction that gives rise to superconductivity. We further argue that long-range Coulomb interaction does not affect the Raman signal for any γ( ⃗ k). We argue that vertex corrections eliminate the divergence at 2⁢Δ max . Here, we also argue that vertex corrections give rise to sharp peaks in R(Ω) at Ω < 2⁢Δ min (the minimum gap along the Fermi surface), when Ω coincides with the frequency of one of the collective modes in a superconductor, e.g., Leggett and Bardasis-Schrieffer modes in the particle-particle channel, and an excitonic mode in the particle-hole channel.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2017

Lattice polarization effects on the screened Coulomb interaction W of the G W approximation

In polar insulators where longitudinal and transverse optical phonon modes differ substantially, the electron-phonon coupling affects the energy-band structure primarily through the long-range Fröhlich contribution to the Fan term. This diagram has the same structure as the GW self-energy where W originates from the electron part of the screened Coulomb interaction. The two can be conveniently combined by combining electron and lattice contributions to the polarizability. Both contributions are nonanalytic at the origin, and diverge as 1/q 2 so that the predominant contribution comes from a small region around q=0. In this work, we adopt a simple estimate forthe Fröhlich contribution by assuming that the entire phonon part can be attributed to a small volume of q near q=0. We estimate the magnitude for q→0 from a generalized Lyddane-Sachs-Teller relation, and the radiusfrom the inverse of the polaron length scale. The gap correction is shown to agree with Fröhlich’s simple estimate -α P ω LO /2 of the polaron effect with α P the polaron coupling factor.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗