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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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7 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2022

Numerical and Experimental Study of a Novel Additively Manufactured Metal-Polymer Composite Heat-Exchanger for Liquid Cooling Electronics

In order to meet increasing power-dissipation requirements of the electronics industry, compact, low-cost, and lightweight heat exchangers (HXs) are desired. With proper design, materials, and manufacture, polymer composite heat exchangers could meet these requirements. This paper presents a novel crossflow air-to-water, low-cost, and lightweight metal-polymer composite HX. This HX, which is entirely additively manufactured, utilizes a novel cross-media approach that provides direct heat exchange between air and liquid sides by using connecting fins. A robust numerical model was developed, which includes the dimensional effects of additive manufacturing. The study consists of a simplified 3D CFD model based on ellipsoidal-shaped staggered tube banks for the laminar range. It then uses an analytical approach to compute entire HX performance. The model is validated experimentally within 8% for thermal performance, 12% for air-side impedance, and 18% for water-side impedance. Finally, HX is compared with a conventional CPU radiator and performs within 10% of the conventional unit for reasonable flow rates and pressure-drop ranges. Moreover, HX also provides added design and cost advantages over the conventional unit, which makes the HX a potential candidate for electronic cooling applications.

30 DIRECT ENERGY CONVERSION↗
DOE OSTI2026

Influence of Surface Treatment on the Interfacial and Mechanical Performance of Metal-Insert Overmolded Composites

Structural composites with metal inserts are gaining increasing interest enabling light weight design for energy efficiency, provide insulation, corrosion protection without compromising mechanical integrity. Such over molded metal-polymer composites show strong potential in many automotive and aerospace component parts, e.g. car bumper, chassis, door, brackets, fasteners, etc. Despite several advantages, metal-polymer dissimilar interface remains a weak spot in structural design, requiring further investigation to improve interfacial interlocking. The current work focuses on enhancing the metal-polymer adhesion between stainless steel inserts and polymer matrices (e.g. acrylonitrile butadiene styrene resin (ABS), and polyamide 66 (PA66) through surface treatment via chemical etching and mechanical roughening. In the chemical etching process, metal substrates were treated with aqua regia solution for different time intervals to evaluate surface roughness measured by water contact angle and morphology analysis. For mechanical roughening approach, metal inserts were subjected to blasting for surface abrasion. Treated samples were also functionalized with aminosilane coupling agent which showed successful grafting on the surface measured by water contact angle. Metal inserts with micro level surface roughness through etching exhibited significant 21% improvement in adhesion strength compared to untreated inserts; however, the effect of silane treatment on the interfacial strength was found to be highly matrix dependent.

Saha, Subhabrata [ORNL] (ORCID:000000033966064X)↗
NASA NTRS1981

Fully plasma-sprayed compliant backed ceramic turbine seal

A seal with a high temperature abradable lining material which encircles the tips of turbine blades in turbomachinery was designed. The seal is directed to maintaining the minimum operating clearances between the blade tips and the lining of a high pressure turbine. A low temperature easily decomposable material in powder form is blended with a high temperature oxidation resistant metal powder. The two materials are simultaneously deposited on a substrate formed by the turbine casing. Alternately, the polymer powder may be added to the metal powder during plasma spraying. A ceramic layer is then deposited directly onto the metal-polymer composite. The polymer additive mixed with the metal is then completely volatilized to provide a porous layer between the ceramic layer and the substrate. Thermal stresses are reduced by the porous structure which gives a cushion effect. No brazing is required by using only plasma spraying for depositing both the powders of the metal and polymer material as well as the ceramic powder.

Bill, R. C.↗
NASA NTRS1993

Property enchancement of polyimide films by way of the incorporation of lanthanide metal ions

Lanthanide metal ions were incorporated into the polyimide derived from 2,2-bis(3,4-dicarboxyphenyl) hexafluoropropane dianhydride (6FDA) and 1,3-bis(aminophenoxy) benzene (APB) in an attempt to produce molecular level metal-polymer composites. The lanthanide series of metal ions (including aluminum, scandium, and yttrium) provide discrete and stable metal ions in the 3+ oxidation state. Throughout the series there is a uniform variation in ionic size ranging from 50 pm for aluminum to a maximum of 103.4 pm for cerium and gradually decreasing again to 84.8 pm for lutetium. The high charge-to-size ratio for these ions as well as the ability to obtain large coordination numbers makes them excellent candidates for interacting with the polymer substructure. The distinct lack of solubility of simple lanthanide salts such as the acetates and halides has made it difficult to obtain metal ions distributed in the polymer framework as discrete ions or metal complexes rather than microcomposites of metal clusters. (Lanthanum nitrates are quite soluble, but the presence of the strongly oxidizing nitrate ion leads to serious degradation of the polymer upon thermal curing. This work was successful at extending the range of soluble metals salts by using chelating agents derived from the beta-diketones dipivaloylmethane, dibenzoylmethane, trifluoroacetylacetone, and hexafluoroacetylacetone. Metal acetates which are insoluble in dimethylacetamide dissolve readily in the presence of the diketones. Addition of the polyimide yields a homogeneous resin which is then cast into a clear film. Upon curing clear films were obtained with the dibenzoylmethane and trifluoroacetylacetone ligands. The dipavaloylmethane precipitates the metal during the film casting process, and hexafluoroacetylacetone gives cured films which are deformed and brittle. These clear films are being evaluated for the effect of the metal ions on the coefficient of thermal expansion, resistance to atomic oxygen, and on selective gas permeability. Much more commonly than above, polyimide films are prepared by casting the film as the poly(amic acid) precursor which is then converted to the imidized form during the thermal cure cycle. Very limited success was achieved in the past in adding lanthanide metal ions to the amide precursors because of gellation and lack of solubility. With the use of the diketone ligands cited above, the solubility and gellation problems were overcome. However, the films after curing were clear but unacceptably brittle. Attempts to overcome this cure embrittlement problem are in progress.

Thompson, David W.↗
DOE OSTI2022

Iodine Capture with Metal-Functionalized Polyacrylonitrile Composite Beads Containing Ag 0 , Bi 0 , Cu 0 , or Sn 0 Particles

The capture of radioiodine from nuclear processes and the mitigation of environmental release are important topic areas of research. Some of the more commonly employed chemisorption-type iodine scavengers reported in the literature are based on metal-exchanged porous sorbents such as Ag-zeolites or metal-functionalized aerogels and xerogels. However, another option is to use zero-valent metals directly that have known high affinities for iodine gas [i.e., I2(g)]. In this study, fine metal particles of Ag0, Bi0, Cu0, and Sn0 were embedded in porous polyacrylonitrile (PAN) substrates at 75 mass% metal loadings within the form of ellipsoidal beads with maximum diameters of ~2–3 mm. These composite beads showed extremely high iodine loadings that are directly related to the metal particle loadings. The X-ray diffraction (XRD) analyses of Ag0, Bi0, Cu0, and Sn0 particles as well as metal-PAN composite beads reacted with iodine gas at 120 ± 1 °C showed phases of AgI, BiI3, CuI, and SnI4, respectively. For the Ag-PAN, Cu-PAN, and Sn-PAN beads, no other crystalline peaks were observed in XRD for unreacted metal or oxidized metals after 48 h in saturated I2(g) at 120 ± 1 °C, whereas unreacted metallic Bi0 was observed within the Bi-PAN composites. However, after a 72 h exposure at 120 ± 1 °C, both the Bi0 particles and the Bi-PAN composites showed full conversion from Bi0 to BiI3 with XRD. Comparisons between mass uptake data and X-ray absorption spectroscopy were used to better understand the phase distribution of the Bi phases present in the Bi-PAN+I composites. The iodine loadings (mg iodine per g sorbent, or qe) for these materials were 1120 (Ag-Particle), 1382 (Bi-Particle-72h), 1033 (Cu-Particle), 3000 (Sn-Particle), 753 (Ag-PAN), 1012 (Bi-PAN-72h), 1457 (Cu-PAN), and 1669 (Sn-PAN). It is possible that inexpensive sorbents such as these could be deployed to help limit or prevent release of radioiodine to the environment.

36 MATERIALS SCIENCE↗