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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 145 records · Page 8
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Rheological behavior and fiber spinning of polyacrylonitrile (PAN)/Carbon nanotube (CNT) dispersions at high CNT loading

Rheological studies play an important role in polymer processing including fiber spinning. In the current work, rheological behavior has been studied for polyacrylonitrile (PAN)/carbon nanotube (CNT) dispersions in dimethyl formamide (DMF), where CNT loading is as high as 15 wt% of the total solids (polymer + CNT). The presence of CNTs increased the elastic-like and shear thinning behavior of the dispersions. The terminal slope of the log G' versus log G" curve, which was used to characterize the homogeneity of solution or dispersion, is dependent on the CNT concentration but independent of temperature between 0 and 60 °C. PAN/CNT-10 (90 wt% PAN +10 wt% CNT) and PAN/CNT-15 were gel spun at different conditions, with small diameter capillary at high shear rate and large diameter capillary at relatively low shear rate. Additionally, for PAN/CNT-10, fiber spinning with lower molecular weight polymer showed increased continuous jetting time when compared to spinning with higher molecular weight polymer. In addition, the rheological behavior of PAN/cellulose nanocrystal (CNC) dispersion with 20–60 wt% CNC was also compared to that of the PAN/CNT dispersions. PAN/CNC and PAN/CNT share similarities in both rheological behavior and fiber spinning at high filler loading.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

Interplay between London Dispersion, Hubbard U , and Metastable States for Uranium Compounds

High-throughput computational studies of lanthanide and actinide chemistry with density-functional theory are complicated by the need for Hubbard U corrections, which ensure localization of the f-electrons, but can lead to metastable states. This work presents a systematic investigation of the effects of both Hubbard U value and metastable states on the predicted structural and thermodynamic properties of four uranium compounds central to the field of nuclear fuels: UC, UN, UO 2 , and UCl 3 . We also assess the impact of the exchange-hole dipole moment (XDM) dispersion correction on the computed properties. Overall, the choice of Hubbard U value and inclusion of a dispersion correction cause larger variations in the computed geometric properties than result from metastable states. Further, the weak dependence of structure optimization on metastable states should simplify future high-throughput calculations on actinides. Conversely, addition of the dispersion correction is found to offset the repulsion introduced by the Hubbard U term and provides greatly improved agreement with experiment for both cell volumes and heats of formation. The XDM dispersion correction is largely invariant to the chosen U value, making it a robust dispersion correction for actinide systems.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2024

Colloidal Stability of PFSA-Ionomer Dispersions. Part I. Single-Ion Electrostatic Interaction Potential Energies

Charged colloidal particles neutralized by a single counterion are increasingly important for many emerging technologies. Attention here is paid specifically to hydrogen fuel cells and water electrolyzers whose catalyst layers are manufactured from a perfluorinated sulfonic acid polymer (PFSA) suspended in aqueous/alcohol solutions. Partially dissolved PFSA aggregates, known collectively as ionomers, are stabilized by the electrostatic repulsion of overlapping diffuse double layers consisting of only protons dissociated from the suspended polymer. We denote such double layers containing no added electrolyte as "single ion". Size-distribution predictions build upon interparticle interaction potential energies from the Derjaguin-Landau-Verwey-Overbeek (DLVO) formalism. However, when only a single counterion is present in solution, classical DLVO electrostatic potential energies no longer apply. Accordingly, here a new formulation is proposed to describe how single-counterion diffuse double layers interact in colloidal suspensions. Part II (Srivastav, H.; Weber, A. Z.; Radke, C. J. Langmuir 2024 DOI: 10.1021/acs.langmuir.3c03904) of this contribution uses the new single-ion interaction energies to predict aggregated size distributions and the resulting solution pH of PFSA in mixtures of n-propanol and water. A single-counterion diffuse layer cannot reach an electrically neutral concentration far from a charged particle. Consequently, nowhere in the dispersion is the solvent neutral, and the diffuse layer emanating from one particle always experiences the presence of other particles (or walls). Thus, in addition to an intervening interparticle repulsive force, a backside osmotic force is always present. With this new construction, we establish that single-ion repulsive pair interaction energies are much larger than those of classical DLVO electrostatic potentials. The proposed single-ion electrostatic pair potential governs dramatic new dispersion behavior, including dispersions that are stable at a low volume fraction but unstable at a high volume fraction and finite volume-fraction dispersions that are unstable with fine particles but stable with coarse particles. Finally, the proposed single-counterion electrostatic pair potential provides a general expression for predicting colloidal behavior for any charged particle dispersion in ionizing solvents with no added electrolyte.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2024

Rheology of bi-disperse dense fiber suspensions

While significant progress has been made in the modeling and simulation of uniform fiber suspensions, no existing model has been validated for industrially-relevant concentrated suspensions containing fibers of multiple aspect ratios. In the present work, we investigate bi-disperse suspensions with two fiber populations in varying aspect ratios in a steady shear flow using direct numerical simulations. Moreover, we measure the suspension viscosity by creating a controlled length bidispersity for nylon fibers suspended in a Newtonian fluid. Here the results showed good agreement between the experimentally measured and numerically predicted viscosity for bi-disperse suspensions. The ratio between the aspect ratio of large to small fibers (size ratio) and the volume fraction of large fibers (composition) in bi-disperse systems strongly affected the rheological behavior of the suspension. The increment of relative viscosity associated with size ratio and composition can be explained by the decrease in the maximum flowable limit or jamming volume fraction. Moreover, the relative viscosity of bi-disperse suspensions collapses, when plotted against the reduced volume fraction, demonstrating the controlling influence of the jamming fraction in bi-disperse fiber suspensions.

42 ENGINEERING↗
DOE OSTI2025

Microbial dispersal into surface soil is limited on a meter scale

Abstract Dispersal shapes microbial communities, yet it is largely unknown how fast or how far free-living microorganisms move in the environment. Here, we deployed microbial traps along transects spanning a grassland and neighboring shrubland to quantify the rate and distance at which microorganisms disperse into the soil surface. We found that bacteria disperse at a similar rate across the two ecosystems, and both bacteria and fungi exhibit a signature of dispersal limitation at a meter scale, indicating highly heterogeneous dispersal of microorganisms into soil.

Environmental Sciences & Ecology↗
DOE OSTI2021

Crossing Symmetric Dispersion Relations in Quantum Field Theories

For 2-2 scattering in quantum field theories, the usual fixed t dispersion relation exhibits only two-channel symmetry. This Letter considers a crossing symmetric dispersion relation, reviving certain old ideas from the 1970s. Rather than the fixed t dispersion relation, this needs a dispersion relation in a different variable z, which is related to the Mandelstam invariants s, t, u via a parametric cubic relation making the crossing symmetry in the complex z plane a geometric rotation. The resulting dispersion is manifestly three-channel crossing symmetric. We give simple derivations of certain known positivity conditions for effective field theories, including the null constraints, which lead to two sided bounds and derive a general set of new nonperturbative inequalities. We show how these inequalities enable us to locate the first massive string state from a low energy expansion of the four dilaton amplitude in type II string theory. We also show how a generalized (numerical) Froissart bound, valid for all energies, is obtained from this approach.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2026

Measurement of the Dispersion in the CeC Beamlines

The coherent electron cooling requires to match the relativistic factors of the hadron and electron beam within 10 -4 accuracy. Initial matching is based on the energy measurement of the electron beam using solenoid with accuracy about 10 -3 (the hadron relativistic factor can be found from the revolution frequency). Further matching is done with observation of the recombination rate with fine tuning based on the cooling rate. The last two steps require change of the electron energy which is achieved by change of the linac voltage. The interaction of the hadron and electron beams is affected by the transverse overlap of two beams. To minimize the effect, we need zero dispersion in the common section. The merge of the beams a dogleg transfer line is used containing two dipoles and three quadrupoles. The zeroing of dispersion is performed by settings of the quadrupoles. We have developed two ways to measure the dispersion. In the first mostly commonly used we change both dipoles by the same value creating the mismatch between the electron energy and bending magnet. In the compensated dogleg the position in the second dipole should not change, and the trajectory angle will change by the same amount as deflecting angle but in opposite direction. Therefore, the trajectory in the common section will not change. The value of the dispersion can be calculated from the beam displacement divided by the relative chang of the dipoles’ current. The second method is based on the change of the electron beam energy using linac. This method requires electron orbit alignment with linac axis to avoid beam steering. The results are shown in Fig.1 and Fig. 2. The first figure shows the dispersion prior the correction, and the second figure after the correction.

43 PARTICLE ACCELERATORS↗
DOE OSTI2023

QES-Plume v1.0: a Lagrangian dispersion model

Low-cost simulations providing accurate predictions of transport of airborne material in urban areas, vegetative canopies, and complex terrain are demanding because of the small-scale heterogeneity of the features influencing the mean flow and turbulence fields. Common models used to predict turbulent transport of passive scalars are based on the Lagrangian stochastic dispersion model. The Quick Environmental Simulation (QES) tool is a low-computational-cost framework developed to provide high-resolution wind and concentration fields in a variety of complex atmospheric-boundary-layer environments. Part of the framework, QES-Plume, is a Lagrangian dispersion code that uses a time-implicit integration scheme to solve the generalized Langevin equations which require mean flow and turbulence fields. Here, QES-Plume is driven by QES-Winds, a 3D fast-response model that computes mass-consistent wind fields around buildings, vegetation, and hills using empirical parameterizations, and QES-Turb, a local-mixing-length turbulence model. In this paper, the particle dispersion model is presented and validated against analytical solutions to examine QES-Plume’s performance under idealized conditions. In particular, QES-Plume is evaluated against a classical Gaussian plume model for an elevated continuous point-source release in uniform flow, the Lagrangian scaling of dispersion in isotropic turbulence, and a non-Gaussian plume model for an elevated continuous point-source release in a power-law boundary-layer flow. In these cases, QES-Plume yields a maximum relative error below 6 % when compared with analytical solutions. In addition, the model is tested against wind-tunnel data for a uniform array of cubical buildings. QES-Plume exhibits good agreement with the experiment with 99 % of matched zeros and 59 % of the predicted concentrations falling within a factor of 2 of the experimental concentrations. Furthermore, results also emphasize the importance of using high-quality turbulence models for particle dispersion in complex environments. Finally, QES-Plume demonstrates excellent computational performance.

58 GEOSCIENCES↗
NASA NTRS1971

The effect of solute additions on the steady-state creep behavior of dispersion-strengthened aluminum.

The effect of solute additions on the steady-state creep behavior of coarse-grained dispersion-strengthened aluminum alloys was studied. Recrystallized dispersion-strengthened solid solutions were found to have stress and temperature sensitivities quite unlike those observed in single-phase solid solutions having the same composition and grain size. The addition of magnesium or copper to the matrix of a recrystallized dispersion-strengthened aluminum causes a decrease in the steady-state creep rate which is much smaller than that caused by similar amounts of solute in single-phase solid solutions. All alloys exhibited essentially a 4.0 power stress exponent in agreement with the model of Ansell and Weertman. The activation energy for steady-state creep in dispersion-strengthened Al-Mg alloys, as well as the stress dependence, was in agreement with the physical model of dislocation climb over the dispersed particles.

Reynolds, G. H.↗
NASA NTRS1975

Abort-once-around entry dispersion corridor analysis

Abort-Once-Around (AOA) entry dispersion corridors were determined for Shuttle Mission 3A. These corridors are presented as plots of entry interface flight path angle versus range to target. The methods used to determine the corridors are discussed. Major dispersion sources are discussed and results presented. While specific trajectory inputs and constraints are subject to change, the dispersion corridors show the trends under consideration. The corridors presented show the delta V advantage of the two-burn over the one-burn AOA. The atmospheric dispersion study illustrates the need to target for the seasonal atmosphere. The 40 deg/30 deg angle of attack (alpha) (TPS design) profile did not provide adequate crossrange capability with worst case aerodynamic dispersions. This problem was alleviated with the change to a 38 deg/28 deg alpha profile. The backface temperatures calculated were generally higher than the present limits.

Kyle, H. C.↗
NASA NTRS1975

Dispersion analysis for baseline reference mission 2

A dispersion analysis considering uncertainties (or perturbations) in platform, vehicle, and environmental parameters was performed for baseline reference mission (BRM) 2. The dispersion analysis is based on the nominal trajectory for BRM 2. The analysis was performed to determine state vector and performance dispersions (or variations) which result from the indicated uncertainties. The dispersions are determined at major mission events and fixed times from liftoff (time slices). The dispersion results will be used to evaluate the capability of the vehicle to perform the mission within a specified level of confidence and to determine flight performance reserves.

Snow, L. S.↗
NASA NTRS1977

Space shuttle engineering and operations support: Dispersion analysis for the first orbital flight test (OFT-1) mission

A dispersion analysis considering 3—sigma (3σ) uncertainties (or perturbations) in platform, vehicle, and environmental parameters has been performed for the first orbital flight test (OFT-1) mission. The dispersion analysis is based on the nominal trajectory for the OFT-1 reference flight profile (RFP) which is described in Reference 1. The analysis has been performed to determine state vector and performance dispersions (or variations) which result from the indicated 3σ uncertainties. The dispersions are determined at major mission events and fixed times from Liftoff (time slices). The dispersion results will be used to evaluate the capability of the vehicle to perform the mission within a 3σ Level of confidence and to determine flight performance reserves. (FPR).

L.S. Snow↗
NASA NTRS1977

Updated dispersion analysis for the first Orbital Flight Test (OFT-1) mission

A dispersion analysis considering 3-sigma uncertainties (or perturbations) in platform, vehicle, and environmental parameters was performed for the first orbital flight test (OFT-1) mission. The dispersion analysis is based on the nominal trajectory for the OFT-1 reference flight profile and was performed to determine state vector and performance dispersions (or variations) which result from the indicated 3 sigma uncertainties. The dispersions are determined at major mission events and fixed times from liftoff (time slices). Principal error contributors to the covariance matrix are listed. The dispersion data indicates that the largest position error occurs in the down range component. At main engine cutoff and circularization, the vehicle performance uncertainties are the major contributors to down range error.

Snow, L. S.↗
NASA NTRS1979

Monte Carlo analysis of satellite debris footprint dispersion

A comprehensive study is performed to investigate satellite debris impact point dispersion using a combination of Monte Carlo statistical analysis and parametric methods. The Monte Carlo technique accounts for nonlinearities in the entry point dispersion, which is represented by a covariance matrix of position and velocity errors. Because downrange distance of impact is a monotonic function of debris ballistic coefficient, a parametric method is useful for determining dispersion boundaries. The scheme is applied in the present analysis to estimate the Skylab footprint dispersions for a controlled reentry. A significant increase in the footprint dispersion is noticed for satellite breakup above a 200,000-ft altitude. A general discussion of the method used for analysis is presented together with some typical results obtained for the Skylab deboost mission, which was designed before NASA abandoned plans for a Skylab controlled reentry.

Rao, P. P.↗
NASA NTRS1982

Velocity dispersions of knots in the Cygnus Loop and IC 443

Very high resolution spectroscopy of optical emission lines indicates that the velocity dispersions of knots in Cygnus Loop and IC 443 filaments result primarily from turbulence within the emitting regions. Line-of-sight velocity dispersions (half-widths at half-maximum) for the observed knots are on the order of 10-30 km/s, including associated thermal velocity dispersions of roughly 15 km/s for hydrogen, 6 km/s for oxygen, and 4 km/s for nitrogen. The knots themselves move randomly relative to each other with speeds of 10-30 km/s. Occasionally, diffuse components of the filaments are observed. These diffuse components have velocity dispersions between 60 and 85 km/s, but the relative contributions of turbulent and thermal motion to the dispersions are unkown.

Shull, P., Jr.↗
NASA NTRS1982

The local dispersion relation for magneto-atmospheric waves

The local dispersion relation for magneto-atmospheric waves is discussed in terms of the linearized theory of waves in a plane-stratified, inviscid, perfectly conducting atmosphere under uniform gravity. The normally used local dispersion relation is demonstrated to not be unique, depending instead on the order of derivation from the fundamental first-order perturbation equations of continuity, momentum, energy, and induction. Furthermore, it is shown that the local dispersion relation predicts that the cutoff frequency decreases with increasing magnetic field strength, while the WKB approximation method projects an increase in the cutoff frequency with increasing magnetic field strength. A new form of the local dispersion relation is developed, and consideration is given to the special case of a global dispersion relation in conditions of an isothermal atmosphere with a horizontal magnetic field.

Thomas, J. H.↗
NASA NTRS1990

Influence of the continuous and dispersed phases on the symmetry of a gas turbine air-blast atomizer

Current trends in liquid-fueled practical combustion systems are leaving less tolerance for fuel injection deficiencies such as poor spray field symmetry. The present paper evaluates the symmetry of the flowfield produced by a practical airblast atomizer. Specifically, the influence of both the continuous phase and dispersed phase on the spray field symmetry is assessed. In the present case, asymmetry in volume flux is associated principally with disparities in the injection of the dispersed phase, which is manifested by a maldistribution of larger drops. Asymmetries observed in the continuous phase without the dispersed phase are reduced in magnitude by the presence of the dispersed phase, but still contribute to asymmetry in radial spread of the dispersed phase.

Mcdonell, V. G.↗
NASA NTRS1990

Constant-dispersion grism spectrometer for channeled spectra

A new spectrometer design is presented in which the angular dispersion with respect to wave number is nearly constant. The spectrometer is a type of grism, a series combination of grating and prism, in which the constant parts of the dispersion terms add to one another but the slopes of the dispersions tend to cancel one another. A systematic method is presented for optimizing the grating and prism parameters. A cross-dispersion technique is presented, eliminating overlapping grating orders. A design example is given for the visible region from 0.45 to 0.80 micron with essentially constant wave-number dispersion and a peak transmission of approximately 95 percent. This grism is well suited for measuring channeled spectra as generated by an optical stellar interferometer.

Traub, Wesley A.↗