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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 127 records · Page 7
All sourcesNASA NTRSDOE OSTI
NASA NTRS1988

Evaluation of chromic acid anodized aluminum foil coated composite tubes for the Space Station truss structure

This paper describes the development and evaluation of chromic acid anodized (CAA) Al foil as a protective and thermal control coating for graphite/epoxy tubes designed for the Space Station truss structure. Special consideration is given to the development of solar-absorptance and thermal-emittance properties required of Al foil, the development of CAA parameters necessary to achieve these optical properties, and the atomic oxygen and UV testing of CAA Al foil. Results showed that 0.003-in CAA Al foil cocured or secondary bonded to graphite/epoxy tubes with thin epoxy film adhesive retains excellent bond strength and provides a superior protective and thermal control coating to the LEO environment. Processes were developed for CAA Al foils long enough to continuously wrap the 23-ft-long diagonal struts of the Space Station truss structure. Specifications are presented for the processes of chromic acid anodizing of Al foil and for the bonding of anodized Al foil to graphite/epoxy tubes.

Dursch, Harry W.↗
NASA NTRS1988

Chromic acid anodizing of aluminum foil

The success of the Space Station graphite/epoxy truss structure depends on its ability to endure long-term exposure to the LEO environment, primarily the effects of atomic oxygen and the temperture cycling resulting from the 94 minute orbit. This report describes the development and evaluation of chromic acid anodized (CAA) aluminum foil as protective coatings for these composite tubes. Included are: development of solar absorptance and thermal emittance properties required of Al foil and development of CAA parameters to achieve these optical properties; developing techniques to CAA 25 ft lengths of Al foil; developing bonding processes for wrapping the Al foil to graphite/epoxy tubes; and atomic oxygen testing of the CAA Al foil. Two specifications were developed and are included in the report: Chromic Acid Anodizing of Aluminum Foil Process Specification and Bonding of Anodized Aluminum Foil to Graphite/Epoxy Tubes. Results show that CAA Al foil provides and excellent protective and thermal control coating for the Space Station truss structure.

Dursch, H.↗
NASA NTRS1962

Pitfalls in thermal emission studies

Attention is called to several pitfalls that often beset investigators who make thermal emittance studies. The pitfalls mentioned include the following: (1) conflicting meanings of several frequently used terms as found in the literature, each meaning having authoritative sponsorship; (2) incomplete and hence potentially misleading descriptions of specimens on which reported data arc based; (3) reference to emissivity or remittance as a property of a surface rather than a volume property (influenced by the surface); (4) occasional omission of diffuse reflection from analyses of the optical properties of inhomogeneous bodies; (5) failure to observe the restrictions upon conditions that are required for validity of basic equations; (6)uncertainties as to the effective temperature, peculiar to specimens having low absorption indices; and (7) lack of suitable physical standards. Several suggestions are made for avoid­ing or minimizing the consequences of the pitfalls discussed.

THERMAL RADIATION↗
DOE OSTI2024

Development of Ti 3 SiC 2 MAX phase tubular structures for solar receiver applications

Solar receiver tubes are key components of concentrating solar-thermal power (CSP) systems that harvest solar energy. For better efficiency, the Gen3 CSP receivers, which collect heat into a heat transfer fluid, require a temperature exceeding 700 °C during operation and need to perform under extreme conditions of high temperature and high thermal stress. Operators are seeking CSP designs using new high-temperature structural materials with high thermal conductivity and high creep resistance to achieve a design life of 30 years and thus help recover the plant capital cost sooner. MAX phase materials, which consist of an early transition metal element, an A-group element, and carbon or nitrogen, are expected to exhibit high creep resistance as well as high fracture toughness. Here, in this paper, we describe fabricating both (1) dense Ti 3 SiC 2 MAX phase disks and (2) short-length tubes using field-assisted sintering technology (FAST). First, the disk samples that we fabricated are fully dense and contain ≈90 % Ti 3 SiC 2 MAX phase materials and ≈10 % TiC phase materials. We determined a flexure strength of 519 ± 32 MPa by conducting a four-point bending test at room temperature with rectangular bar samples of ≈100 % density. The thermal conductivity of the Ti 3 SiC 2 MAX phase samples, measured by light flashing analysis, decreases linearly from a value of 41 W . m -1 . K -1 at room temperature to a value of 36 W . m -1 . K -1 at 650 °C. A solar reflectance measurement of the Ti 3 SiC 2 MAX phase revealed that, temperature increases from 400 to 1400 °C, thermal emittance increases from 0.39 to 0.49, while selectivity decreases from 1.8 to 1.4, respectively. Whereas the surface oxidized MAX phase samples after 100 h exposure to air at 1000 °C exhibit that of SiC. Next, we discuss fabrication of the crack-free Ti 3 SiC 2 MAX phase tubular structures accomplished by using FAST processing in graphite bedding. A Ti 3 SiC 2 MAX phase content of > 95 % with traceable ≈3% remaining TiC phase and ≈15 % porosity were demonstrated after high-temperature annealing. An average fracture strength of ≈250 MPa was determined with Ti 3 SiC 2 MAX phase tubes of ≈85 % density by diametral compression testing at room temperature. Our work demonstrated that using FAST processing to produce Ti 3 SiC 2 MAX phase tubular structures for CSP receiver applications is a viable approach.

14 SOLAR ENERGY↗
DOE OSTI2025

Large area transparent refractory aerogels with high solar thermal performance

Application of transparent silica aerogels in low-temperature solar thermal systems has led to major improvements in performance. In high temperature concentrating solar thermal (CST) systems, aerogels have yet to demonstrate the necessary scalability, durability, and performance to support their widespread deployment. Here, large-area transparent refractory aerogel tiles are synthesized and shown to achieve a record-high receiver figure-of-merit (FOM) at high temperatures. The work leverages a scaled-up process for sol–gel synthesis to control the density of the aerogels for improved solar transmittance and adapts a previous atomic layer deposition (ALD) technique with the aid of predictive reaction-transport modeling. After aging for 10 days at 700 °C, the large-area tiles exhibit a solar-weighted transmittance of 95.6 % and a thermal emittance of 0.31, corresponding to a FOM of 80 % at 100 suns and 700 °C. The observed sintering rates at 700 °C are comparably low to earlier one-inch aerogels, suggesting long-term stability under relevant operating conditions. Furthermore, the study indicates that refractory aerogels are scalable materials for efficient photothermal conversion at high temperatures.

Aerogels↗
NASA NTRS1997

Investigation of Teflon FEP Embrittlement on Spacecraft in Low Earth Orbit

Teflon(registered trademark) FEP (fluorinated ethylene-propylene) is commonly used on exterior spacecraft surfaces in the low Earth orbit (LEO) environment for thermal control. Silverized or aluminized FEP is used for the outer layer of thermal control blankets because of its low solar absorptance and high thermal emittance. FEP is also preferred over other spacecraft polymers because of its relatively high resistance to atomic oxygen erosion. Because of its low atomic oxygen erosion yield, FEP has not been protected in the space environment. Recent, long term space exposures such as on the Long Duration Exposure Facility (LDEF, 5.8 years in space), and the Hubble Space Telescope (HST, after 3.6 years in space) have provided evidence of LEO environmental degradation of FEP. These exposures provide unique opportunities for studying environmental degradation because of the long durations and the different conditions (such as differences in altitude) of the exposures. Samples of FEP from LDEF and from HST (retrieved during its first servicing mission) have been evaluated for solar induced embrittlement and for synergistic effects of solar degradation and atomic oxygen. Micro-indenter results indicate that the surface hardness increased as the ratio of atomic oxygen fluence to solar fluence decreased for the LDEF samples. FEP multilayer insulation (MLI) retrieved from HST provided evidence of severe embrittlement on solar facing surfaces. Micro-indenter measurements indicated higher surface hardness values for these samples than LDEF samples, but the solar exposures were higher. Cracks induced during bend testing were significantly deeper for the HST samples with the highest solar exposure than for LDEF samples with similar atomic oxygen fluence to solar fluence ratios. If solar fluences are compared, the LDEF samples appear as damaged as HST samples, except that HST had deeper induced cracks. The results illustrate difficulties in comparing LEO exposed materials from different missions. Because the HST FEP appears more damaged than LDEF FEP based on depth of embrittlement, other causes for FEP embrittlement in addition to atomic oxygen and ultraviolet (UV) radiation, such as thermal effects and the possible role of soft x-ray radiation, need to be considered. FEP that was exposed to soft x-rays in a ground test facility, showed embrittlement similar to that witnessed in LEO, which indicates that the observed differences between LDEF and HST FEP might be attributed to the different soft x-ray fluences during these two missions.

deGroh, Kim K.↗
DOE OSTI2020

Widely Tunable Optical and Thermal Properties of Dirac Semimetal Cd 3 As 2

In this paper, a detailed analysis of the temperature-dependent optical properties of epitaxially grown cadmium arsenide (Cd 3 As 2 ), a newly discovered 3D Dirac semimetal is reported. Fermi level tuning—instigated from Pauli-blocking in the linear Dirac cone—and varying Drude response, generate large variations in the mid- and far-infrared optical properties. Thermo-optic shifts larger than those of traditional III–V semiconductors are demonstrated. Electron scattering rate, plasma frequency edge, Fermi level shift, optical conductivity, and electron effective mass analysis of Cd 3 As 2 thin-films are quantified and discussed in detail. The ab initio density functional study and experimental analysis of epitaxially grown Cd 3 As 2 promise applications for nanophotonic and nanoelectronic devices, such as reconfigurable metamaterials and metasurfaces, nanoscale thermal emitters, and on-chip directional antennas.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Plasmon-Enhanced Greenhouse Selectivity for High-Temperature Solar Thermal Energy Conversion

The greenhouse effect arises when thermal radiation is forced to undergo absorption and re-emission many times before escaping, while sunlight transmits largely unimpeded. Although this effect is responsible for global warming, it is generally weak in solid-state materials because radiation can be easily overpowered by other modes of heat transfer. Here, we report on the use of infrared plasmonic nanoparticles to enhance the greenhouse effect in transparent mesoporous materials. Local surface plasmon resonances in transparent conducting oxide nanoparticles (TCO NPs) selectively shorten the mean free path of thermal photons while maintaining high solar transmittance. The addition of a small amount of TCO NPs (<0.1% by volume) nearly halves the heat losses at 700 °C. This leads to an experimentally demonstrated effective thermal emittance of ~0.17 at 700 °C, which is the lowest reported value to date, among all selective surfaces and transparent insulating materials measured at 650 °C or above. Furthermore, our results show that plasmon-enhanced greenhouse selectivity (PEGS) is a promising mechanism for spectral control of radiative heat transfer, and more specifically, for conversion of minimally concentrated sunlight into high-temperature heat.

14 SOLAR ENERGY↗
DOE OSTI2021

Machine learning framework for quantum sampling of highly constrained, continuous optimization problems

In recent years, there is growing interest in using quantum computers for solving combinatorial optimization problems. In this work, we developed a generic, machine learning-based framework for mapping continuous-space inverse design problems into surrogate quadratic unconstrained binary optimization (QUBO) problems by employing a binary variational autoencoder and a factorization machine. The factorization machine is trained as a low-dimensional, binary surrogate model for the continuous design space and sampled using various QUBO samplers. Using the D-Wave Advantage hybrid sampler and simulated annealing, we demonstrate that by repeated resampling and retraining of the factorization machine, our framework finds designs that exhibit figures of merit exceeding those of its training set. We showcase the framework’s performance on two inverse design problems by optimizing (i) thermal emitter topologies for thermophotovoltaic applications and (ii) diffractive meta-gratings for highly efficient beam steering. This technique can be further scaled to leverage future developments in quantum optimization to solve advanced inverse design problems for science and engineering applications.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2020

Multiple Tunable Hyperbolic Resonances in Broadband Infrared Carbon-Nanotube Metamaterials

Aligned densely packed carbon-nanotube metamaterials prepared using vacuum filtration are an emerging infrared nanophotonic material. We report multiple hyperbolic plasmon resonances, together spanning the mid-infrared, in individual resonators made from aligned and densely packed carbon nanotubes. In a near-field scanning optical microscopy (NSOM) imaging study of nanotube metamaterial resonators, we observe distinct deeply subwavelength field profiles at the fundamental and higher-order resonant frequencies. The wafer-scale area of the nanotube metamaterials allows us to combine this near-field imaging with a systematic far-field spectroscopic study of the scaling properties of many resonator arrays. Thorough theoretical modeling agrees with these measurements and identifies the resonances as higher-order Fabry-Perot (FP) resonances of hyperbolic waveguide modes. Nanotube resonator arrays show broadband extinction from 1.5–10 µm and reversibly switchable extinction in the 3–5 µm atmospheric transparency window through the coexistence of multiple modes in individual ribbons. Broadband carbon-nanotube metamaterials supporting multiple resonant modes are a promising candidate for ultracompact absorbers, tunable thermal emitters, and broadband sensors in the mid-infrared.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Accurate calibration of thermophotovoltaic efficiency

Abstract The new record efficiency in Thermophotovoltaics relies upon a highly reflective rear mirror. The excellent rear mirror boosts voltage by enhancing the luminescence extraction, and separately also reflects low energy photons, which would otherwise be useless in thermophotovoltaics. The reflected low energy photons reheat the thermal emitter, and regenerate above-bandgap energy photons. The efficiency calibration for such regenerative thermophotovoltaics depends on several factors, yet predominantly on the accurate measurement of the rear mirror reflectivity. Here, we report on the technique for accurate measurement of mirror reflectivity, and of record thermophotovoltaic efficiency 29.1 ± 0.6%, at 1207 °C.

14 SOLAR ENERGY↗
DOE OSTI2022

A Very High Temperature Lead Cooled Microreactor Concept using Advanced Materials and Thermophotovoltaics Direct Energy Conversion Technology

Recently, significant advances have been made in designing high-temperature capable nuclear fuels. In parallel, important advances have occurred in design of nanophotonic structures (coatings) with ability to shape the frequencies of light being emitted from hot surfaces. In this project, we bring these materials advances together into a design for a new direct conversion nuclear powered system with high thermodynamic efficiency, inherent safety, and unprecedented reduction in size and weight relative to current designs. The concept involves using the heat generated from nuclear fission to raise the temperature of a selective thermal emitter to >800°C. The selective emitter shifts the normal broad brand emissions of light from its hot surface into the correct near- and mid-IR bands that produce electricity with inexpensive photovoltaic cells. We have designed a new annular flow Lead Fast Reactor (LFR) that minimizes overall reactor/power conversion footprint. The results indicate that the overall microreactor/power-system design offers a 2X reduction in size over existing technology that is based on the sCO 2 reverse compression Brayton cycle. Additionally, the only moving part in our design is a circulation pump to cool the PVT panels.

21 SPECIFIC NUCLEAR REACTORS AND ASSOCIATED PLANTS↗
NASA NTRS1970

Series emittance coatings

Series emittance thermal control coatings of polymeric dielectric films overlaying reflectors vacuum exposed to UV, X ray and proton radiation

Griffin, R.↗