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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 595 records · Page 33
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

The role of collective elasticity on activated structural relaxation, yielding, and steady state flow in hard sphere fluids and colloidal suspensions under strong deformation

In this work, we theoretically study the effect of external deformation on activated structural relaxation and aspects of the nonlinear mechanical response of glassy hard sphere fluids in the context of elastically collective nonlinear Langevin equation theory. This microscopic force-based approach describes activated relaxation as a coupled local–nonlocal event involving caging and longer range collective elasticity, with the latter becoming more important and ultimately dominant with increasing packing fraction under equilibrium conditions. The central new question we address is how this physical picture of activated relaxation, and the relative importance of local caging vs collective elasticity physics, depends on external deformation. Theoretical predictions are presented for deformation-induced enhancement of mobility, the onset of relaxation speed up at remarkably low values of stress, strain, or shear rate, apparent power law thinning of the steady state structural relaxation time and viscosity, a non-vanishing activation barrier in the shear thinning regime, an apparent Herschel–Bulkley form of the rate dependence of the steady state shear stress, exponential growth of different measures of a dynamic yield or flow stress with the packing fraction, and reduced fragility and dynamic heterogeneity under deformation. The results are contrasted with experiments and simulations, and qualitative or better agreement is found. An overarching conclusion is that deformation strongly reduces the importance of longer range collective elastic effects relative to the local caging aspect for most, but not all, physical questions, with deformation-dependent fragility and dynamic heterogeneity phenomena being qualitatively sensitive to collective elasticity. Overall, nonlinear rheology is predicted to be a more local problem than quiescent structural relaxation, albeit with deformation-modified activated processes still important.

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

Surrogate Suspension-Resuspension Study

The objective of this study was to conduct a series of tests looking at the deposition and resuspension of aerosol particles deposited onto multiple representative substrate surfaces for a range of particle sizes under varying environmental conditions. The benefit of this study is to provide additional insight into the understanding of early time resuspension from different mechanisms and compare to existing literature. The resuspension methods utilized in this study were full-scale and the substrates were representative of real- world ground level conditions. Multiple experiments were conducted to assess the impact on resuspension from the varying substrates and mechanisms. The results of this study show variations in the size distribution of aerosol as a function of height from the source resuspension factors. Additionally, the aerosolized mass concentration and resuspension factor were evaluated. The maximum resuspension factor was found to be on the order of 10 -4 m -1 which is higher than most resuspension factors found in literature but represents idealized conditions due to the well constrained experimental setup.

36 MATERIALS SCIENCE↗
DOE OSTI2024

UO 2 -Liquid Metal Suspension Fuel Concept: Alloy Selection and Depletion Calculations

A novel nuclear fuel was recently proposed that consists of UO 2 particles suspended in a liquid metal mixture. Two liquid metal candidates were identified: BiPbSn and PbSn. Scoping simulations were performed on an over-simplified reactor core that showed a potential limit on achievable burnup. Those findings led to two questions that needed to be addressed: What is the corrosion behavior of the liquid metals toward Zircaloy-4 (Zr4)? And what level of burnup can the fuel be expected to achieve? This report documents efforts to answer both of those questions. First, corrosion experiments were performed between the liquid metal candidates and Zr4 coupons. Second, the previous scoping simulations were expanded to include depletion analyses so that maximum burnups could be estimated. At 400°C, neither PbSn nor BiPbSn caused significant corrosion to the Zr4 coupons. At 600°C, BiPbSn did not cause significant corrosion, but PbSn did. In addition, pure bismuth and pure tin were both highly corrosive, whereas pure lead was non-corrosive. The depletion simulations found that low-enriched fuel could maintain light-water reactor operating temperatures but achieve a burnup of only about one-third of existing reactors. Higher enrichments could achieve burnups equal to or higher than those of existing reactors but at the expense of higher operating temperatures.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
NASA NTRS1970

Safe suspension of specimens or clusters during dynamic testing - A concept

Support system without point supports permits dynamic testing of complex or delicate mechanical units without excessive movement which might cause damage. Motion-sensor pressure-control system regulates inflation of molded rubber bags surrounding test specimen, so that any excessive motion is smothered until test is terminated.

Hoch, G. C.↗
NASA NTRS1971

Pyrotechnic hazards classification and evaluation program. Run-up reaction testing in pyrotechnic dust suspensions

A preliminary investigation of the parameters included in run-up dust reactions is presented. Two types of tests were conducted: (1) ignition criteria of large bulk pyrotechnic dusts, and (2) optimal run-up conditions of large bulk pyrotechnic dusts. These tests were used to evaluate the order of magnitude and gross scale requirements needed to induce run-up reactions in pyrotechnic dusts and to simulate at reduced scale an accident that occurred in a manufacturing installation. Test results showed that propagation of pyrotechnic dust clouds resulted in a fireball of relatively long duration and large size. In addition, a plane wave front was observed to travel down the length of the gallery.

Source record↗
NASA NTRS1973

Free suspension processing of oxides to form amorphous oxide materials, appendix B

The processing of yttria, zirconia, and alumina under weightless conditions is discussed. The process consists of levitation or position control, heating and melting, superheating, and supercooling. The use of arc imaging furnaces, lasers, induction heating, microwave, and electron beam methods are analyzed to show the advantages and disadvantages of each.

Wouch, G.↗