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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 1,441 records · Page 80
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Strain-Enhanced Metallic Intermixing in Shape-Controlled Multilayered Core–Shell Nanostructures: Toward Shaped Intermetallics

Controlling the surface composition of shaped bimetallic nanoparticles could offer precise tunability of geometric and electronic surface structure for new nanocatalysts. To achieve this goal, a platform for studying the intermixing process in a shaped nanoparticle was designed, using multilayered Pd-Ni-Pt core–shell nanocubes as precursors. Under mild conditions, the intermixing between Ni and Pt could be tuned by changing layer thickness and number, triggering intermixing while preserving nanoparticle shape. Intermixing of the two metals is monitored using transmission electron microscopy. The surface structure evolution is characterized using electrochemical methanol oxidation. DFT calculations suggest that the low-temperature mixing is enhanced by shorter diffusion lengths and strain introduced by the layered structure. The platform and insights presented are an advance toward the realization of shape-controlled multimetallic nanoparticles tailored to each potential application.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2018

Study of Creep and Damage for a Hollow Cylinder on the Basis of Space and Refined Shell Models

We consider the axisymmetric problem of creep and creep damage of a hollow cylinder and develop a numerical-analytic method for the solution of this nonlinear initial-boundary-value problem. We also present an example of evaluation of creep and the time to fracture for a cylinder loaded by internal pressure. The results accumulated by using a three-dimensional model are compared with the data obtained on the bases of the refined model of the theory of shells.

97 MATHEMATICS AND COMPUTING↗
DOE OSTI2022

Hierarchical 3D Printed Porous Silicones with Porosity Derived from Printed Architecture and Silicone-Shell Microballoons

A method is reported to prepare siloxane microballoons that can be loaded into a direct ink write siloxane ink for 3D printing. The resulting structure is subjected to a solvent removal and supercritical drying process to provide a final printed siloxane having both macroscopic and microscopic porosity. Core-shell particles are generated by an emulsion template and phase separation process. Intra-strand closed-cell porosities can be achieved between 10 and 40 vol% thus facilitating additional compressive strain before lockup. Here short term compression set testing highlights the excellent shape retention properties of these elastomers, which have less than 8% relative compression set under load.

36 MATERIALS SCIENCE↗
DOE OSTI2019

State-selective and total cross sections for electron capture from the K-shell of multi-electron atoms by fully stripped projectiles

Capture of a K-shell electron by bare fast ions H{sup +}, He{sup 2+} and Li{sup 3+} from multi-electron atomic targets (carbon, nitrogen, oxygen, neon and argon) is theoretically studied by means of the four-body boundary-corrected first Born approximation. In a wide impact energy interval ranging from 100 to 40 000 keV/amu, extensive tables of the obtained state-selective cross sections Q{sub nlm} are presented for each individual final hydrogen-like state described by the usual quantum numbers {n,l,m}. The total cross sections Q{sub nl}, Q{sub n} and Q{sub tot} for capture summed over the quantum numbers m, {l,m} and {n,l,m}, respectively, are also reported. Theoretical cross sections Q{sub tot} are found to compare favorably with the corresponding experimental data. The maximal value of the principal quantum number n has been taken to be n=4, which satisfies the relationship n≥Z{sub P}, where Z{sub P} is the nuclear charge of the projectile. The tabulated state-selective cross sections Q{sub nlm} for single-electron capture by swift nuclei from multi-electron atoms are the first results in the literature on the theory of four-body collisions. The present data for the examined capture processes are of notable interest for many fundamental and applied problems in various interdisciplinary fields ranging from fusion research, plasma physics, astrophysics to radiotherapy.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2023

Enhanced low temperature performance of bimetallic Pd/Pt/SiO 2 (core)@Zr(shell) diesel oxidation catalysts

Here, in this study, the diesel oxidation performance of degreened (DG) and hydrothermally aged monometallic and bimetallic Pd/Pt/SiO 2 (core)@Zr(shell) catalysts with varying Pd/Pt molar ratios from 3/1–1/3 was evaluated. Pd/Pt(3/1)/SiO 2 @Zr (DG) achieved 50% and 90% conversion of CO at 166 °C (T 50 ), 169 °C (T 90 ) and total hydrocarbons (THCs) at 198 °C (T 50 ), 244 °C (T 90 ). Decreasing the Pd/Pt molar ratio led to a decrease in the T 50,90 ’s, with Pd/Pt(1/3)/SiO 2 @Zr (DG) achieving T 50,90 ’s at 153, 156 °C for CO and 171, 200 °C for THCs, respectively. Moreover, Pd/Pt(1/3)/SiO 2 @Zr showed enhanced hydrothermal stability. XRD and TEM showed that in the hydrothermally aged bimetallic catalysts, the fraction of Pd present as a Pt-Pd metallic alloy increased with Pt content. The enhanced low temperature performance of Pd/Pt(1/3)/SiO 2 @Zr compared to the other studied catalysts was attributed to Pd being primarily present in metallic form, despite being subjected to severe oxidizing conditions.

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

Modeling of deformation of battery cells using thick shell element formulation

Here, we describe a new approach for modeling nonlinear deformation and stress distribution of battery cells using a new thick shell finite element formulation with a through-thickness calculation of stresses and strains that satisfy equilibrium conditions. Battery cells are transversely layered materials that contain numerous thin layers in a repeating sequence. The layers are made of materials with significantly different mechanical responses. Explicit discretization of the layers is computationally impractical except for very small domains, while homogenized material models cannot account for stress and strain variations and partition through the thickness. The new formulation allows for calculation of the transverse and interlayer stresses based on the material properties of the individual cell layers. The application to problems where the transverse stresses have strong influence is also possible.

25 ENERGY STORAGE↗
DOE OSTI2021

Isogeometric Bézier dual mortaring: The Kirchhoff–Love shell problem

Here in this paper we develop an isogeometric Bézier dual mortar method for coupling multi-patch Kirchhoff–Love shell structures. The proposed approach weakly enforces the continuity of the solution at patch interfaces through a dual mortar method and can be applied to both conforming and non-conforming discretizations. As the employed dual basis functions have local supports and satisfy the biorthogonality property, the resulting stiffness matrix is sparse. In addition, the coupling accuracy is optimal because the dual basis possesses the polynomial reproduction property. We also formulate the continuity constraints through the Rodrigues’ rotation operator which gives a unified framework for coupling patches that are intersected with G 1 continuity as well as patches that meet at a kink. Several linear and nonlinear examples demonstrated the performance and robustness of the proposed coupling techniques.

42 ENGINEERING↗
DOE OSTI2019

Modulation and splitting of three-body radiative heat flux via graphene/SiC core-shell nanoparticles

Here, we theoretically demonstrate the modulation and splitting of radiative heat flux in a three-body system consisting of graphene/SiC core-shell (GSCS) nanoparticles on the basis of their highly tunable polarizabilities, which play a dominant role in the coupling of localized surface resonance. The excitation of multiple photon tunneling modes enables the radiative heat transfer to be controlled in different scenarios. Using the dependence of photon tunneling on the Fermi level and radius of the intermediate GSCS nanoparticle, such a many-body system not only holds the potential to be a near-field thermal modulator with a thermal modulation ratio greater than 40, but also allows the heat splitting effect with the ratio over 99 when the intermediate particle becomes the hot source. This work may facilitate dynamical thermal management in a many-body system, and can also benefit the plasmonics community in the near future.

42 ENGINEERING↗
DOE OSTI2017

Reaction mechanism for oxygen evolution on RuO 2 , IrO 2 , and RuO 2 @IrO 2 core-shell nanocatalysts

Iridium dioxide, IrO 2 , is second to the most active RuO 2 catalyst for the oxygen evolution reaction (OER) in acid, and is used in proton exchange membrane water electrolyzers due to its high durability. In order to improve the activity of IrO 2 -based catalysts, we prepared RuO 2 @IrO 2 core-shell nanocatalysts using carbon-supported Ru as the template. At 1.48 V, the OER specific activity of RuO 2 @IrO 2 is threefold that of IrO 2 . While the activity volcano plots over wide range of materials have been reported, zooming into the top region to clarify the rate limiting steps of most active catalysts is important for further activity enhancement. Here, we verified theory-proposed sequential water dissociation pathway in which the O—O bond forms on a single metal site, not via coupling of two adsorbed intermediates, by fitting measured polarization curves using a kinetic equation with the free energies of adsorption and activation as the parameters. Consistent with theoretical calculations, we show that the OER activities of IrO 2 and RuO 2 @IrO 2 are limited by the formation of O adsorbed phase, while the OOH formation on the adsorbed O limits the reaction rate on RuO 2 .

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2018

Optimization of the radio frequency power, time and cooling water temperature for pasteurization of Salmonella Typhimurium in shell eggs

Here, radio frequency (RF) power, treatment time and cooling water temperature affect inactivation of Salmonella Typhimurium in shell eggs and internal quality. Eggs were processed using 40.68 MHz RF at 30–45 W, 2.5–8 min and 30–38 °C, followed by hot water (HW) treatment at 56.7 °C for 15 min. Five conditions achieved >5 log reduction of Salmonella without observable quality change. Analyses of the longest (8 min at 30 W and 30 °C) and shortest (4.5 min at 35 W and 38 °C) treatments indicated that combined RF/HW treatments significantly (P < 0.05) preserved quality better than HW pasteurization (56.7 °C for 60 min). No significant (P ≥ 0.05) difference in egg quality was observed between the longest and shortest treatment, except that the shortest resulted in greater albumen turbidity. As the longest treatment required 78% more time and 47% more energy than the shortest, industry may wish to use the shortest RF treatment time.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2025

Surface roughness and dimensional evaluation of laser powder bed fusion additively manufactured shell and tube heat exchangers

The growing interest in additively manufactured (AM) heat exchangers drove the need to understand how this construction technique impacts heat exchanger performance. Two primary factors driven by AM that influence heat exchanger performance are surface roughness and geometry. To better understand these parameters, a range of shell and tube heat exchangers constructed using laser powder bed fusion were evaluated. Of those evaluated, the surface roughness throughout a fourteen-tube, zero-baffle heat exchanger was measured using computed tomography. Between the inner and outer tubes, the inner tube surfaces had a greater surface roughness than the outer by 8.07 μm, while the surfaces at the top of the build volume had higher surface roughness values than the bottom. Dimensionally, the inner tube diameters of this heat exchanger were 0.15% different from the design value, while the outer diameters were within a 0.84 % difference. Manual measurements across seven other heat exchangers yielded a maximum 1.15% difference between the design and measured diameters. Across the build volume for all heat exchangers studied, the tube diameters at the top were larger than at the bottom by a maximum of 1.24% difference. Inconsistent melting throughout the individual parts and the build volume, as well as particle splatter and thermal gradient variation were attributed to the surface roughness and dimensional changes seen. These results strengthen the knowledge of dimensional and surface roughness considerations when designing AM heat exchangers.

36 MATERIALS SCIENCE↗