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At least 271 records · Page 15
All sourcesNASA NTRSDOE OSTI
DOE OSTI2023

Efficient Reformulation of Linear and Nonlinear Solid-Phase Diffusion in Lithium-ion Battery Models using Symmetric Polynomials: Mass Conservation and Computational Efficiency

Lithium-ion batteries are typically modeled using porous electrode theory coupled with various transport and reaction mechanisms, along with suitable discretization or approximations for the solid-phase diffusion equation. The solid-phase diffusion equation represents the main computational burden for typical pseudo-2-dimensional (p2D) models since these equations in the pseudo r -dimension must be solved at each point in the computational grid. This substantially increases the complexity of the model as well as the computational time. Traditional approaches towards simplifying solid-phase diffusion possess certain significant limitations, especially in modeling emerging electrode materials which involve phase changes and variable diffusivities. A computationally efficient representation for solid-phase diffusion is discussed in this paper based on symmetric polynomials using Orthogonal Collocation and Galerkin formulation (weak form). A systematic approach is provided to increase the accuracy of the approximation (p form in finite element methods) to enable efficient simulation with a minimal number of semi-discretized equations, ensuring mass conservation even for non-linear diffusion problems involving variable diffusivities. These methods are then demonstrated by incorporation into the full p2D model, illustrating their advantages in simulating high C-rates and short-time dynamic operation of Lithium-ion batteries.

25 ENERGY STORAGE↗
NASA NTRS1983

Evolutionary effects of helium diffusion in population II stars

Evolutionary calculations continuing until well past turnoff are presented for models of low-mass Population II stars which take into account the effects of the diffusion of helium relative to hydrogen. Evolutionary tracks, cluster isochrones and hydrogen distributions were obtained for stellar masses in the range 0.75 to 1.01 solar masses, both in the presence and absence of diffusion. It is found that for a star of a given mass, diffusion speeds up the evolutionary process on the main sequence, although after turnoff evolution is slowed with respect to the case without diffusion. As the stars ascend the red giant branch, their outer regions are remixed so that evidence of helium diffusion is erased, and the evolutionary tracks of the models with and without diffusion converge. Thus, if the age of a globular cluster is determined from the absolute magnitude at turnoff or from fitting isochrones, diffusion results in a 25% reduction in the derived age at a turnoff magnitude of 4.23, and a 14% reduction at a turnoff magnitude of 3.45.

Stringfellow, G. S.↗
DOE OSTI2024

DRIFT: Diffusivity Regulation of Isotopes by nanoconFinementT

Spontaneous isotope fractionation has been reported under nanoconfinement conditions in naturally occurring systems, but the origin of this phenomena is currently unknown. Two existing hypotheses have been proposed, one based on changes in the solvation environment of the isotopes that reduces the non-mass dependent hydrodynamics contribution to diffusion. The other is that isotopes have mass-dependent surface adsorption, varying their total diffusion through nanoconfined channels. To investigate these hypotheses, benchtop experiments, nuclear magnetic resonance (NMR) spectroscopy, and molecule scale modeling were applied. Classical molecular dynamics simulations identified that the Na + and Cl - hydration shells across the three different salt solutions ( 22 Na 35 Cl, 23 Na 35 Cl, 24 Na 35 Cl) did not vary as a function of the Na + isotope, but that there was a significant pore size effect, with larger hydration shells at larger pore sizes. Additionally, while total adsorption times did not vary as a function of the Na + isotope or pore size, the free ion concentration, or those adsorbed on the surface for <5% of the simulation time did exhibit isotope dependence. Experimentally, challenges occurred developing a repeatable experiment, but NMR characterization of water diffusion rates through ordered alumina membranes was able to identify the existence of two distinct water environments associated with water inside and outside the pore. Further NMR studies could be used to confirm variation in hydration shells and diffusion rates of dissolved ions in water. Ultimately, mass-dependence adsorption is a primary driver of variations in isotope diffusion rates, rather than variation in hydration shells that occur under nanoconfinement.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2020

Mechanistic understanding of catalytic conversion of ethanol to 1-butene over 2D-pillared MFI zeolite

Ethanol is an important C2 platform molecule for producing value-added chemicals and distillate hydrocarbon fuels (e.g., jet and diesel). Among these, catalytic upgrading of ethanol to butenes can generate valuable commodity chemicals (e.g., 1-butene) and provide C4 olefin intermediates that can be further upgraded to jet/diesel fuels. 2D zeolites offer hierarchical mesoporous structures, leading to improved mass transport and reduced diffusion length, which can help to address the coking challenges faced by ethanol conversion to hydrocarbons over 3D zeolites. In this study, we investigate the acid-catalyzed conversion of ethanol to 1-butene over the Brønsted acid sites (BAS) in 2D-pillared MFI zeolite (2D-PMFI) using ab initio molecular dynamics (AIMD) simulations, in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), and calorimetric measurements. A detailed thermodynamic analysis, using quasi-harmonic approximation (QHA), on the Gibbs free energy pathway of ethanol conversion shows that the consideration of entropy is critical to accurately capture the detailed thermodynamic profiles. The formation of bulky ethoxy-ethene complex is found to be a potential rate-determining step (RDS), proceeding via stepwise mechanism. The reactivity of 2D-PMFI can be further tuned by manipulating RDS through a careful control of number of BAS and operating temperatures. The accuracy of computational model is confirmed through the comparison of calculated vibrational density of states (VDOS) against the experimental DRIFTS measurements. Overall, our study provides mechanistic insights into ethanol upgrading over the 2D-PMFI and shows the importance of evaluating entropic effects in such confined system.

Ethanol conversion, 2D-pillared zeolite, MFI, Anha↗
DOE OSTI2021

Estimation of secondary organic aerosol viscosity from explicit modeling of gas-phase oxidation of isoprene and α -pinene

Abstract. Secondary organic aerosols (SOA) are major components of atmospheric fine particulate matter, affecting climate and air quality. Mounting evidence exists that SOA can adopt glassy and viscous semisolid states, impacting formation and partitioning of SOA. In this study, we apply the GECKO-A (Generator of Explicit Chemistry and Kinetics of Organics in the Atmosphere) model to conduct explicit chemical modeling of isoprene photooxidation and α-pinene ozonolysis and their subsequent SOA formation. The detailed gas-phase chemical schemes from GECKO-A are implemented into a box model and coupled to our recently developed glass transition temperature parameterizations, allowing us to predict SOA viscosity. The effects of chemical composition, relative humidity, mass loadings and mass accommodation on particle viscosity are investigated in comparison with measurements of SOA viscosity. The simulated viscosity of isoprene SOA agrees well with viscosity measurements as a function of relative humidity, while the model underestimates viscosity of α-pinene SOA by a few orders of magnitude. This difference may be due to missing processes in the model, including autoxidation and particle-phase reactions, leading to the formation of high-molar-mass compounds that would increase particle viscosity. Additional simulations imply that kinetic limitations of bulk diffusion and reduction in mass accommodation coefficient may play a role in enhancing particle viscosity by suppressing condensation of semi-volatile compounds. The developed model is a useful tool for analysis and investigation of the interplay among gas-phase reactions, particle chemical composition and SOA phase state.

54 ENVIRONMENTAL SCIENCES↗
NASA NTRS2012

Mass and Momentum Transport in Microcavities for Diffusion-Dominant Cell Culture Applications

For the informed design of microfluidic devices, it is important to understand transport phenomena at the microscale. This letter outlines an analytically-driven approach to the design of rectangular microcavities extending perpendicular to a perfusion microchannel for microfluidic cell culture devices. We present equations to estimate the spatial transition from advection- to diffusion-dominant transport inside cavities as a function of the geometry and flow conditions. We also estimate the time required for molecules, such as nutrients or drugs to travel from the microchannel to a given depth into the cavity. These analytical predictions can facilitate the rational design of microfluidic devices to optimize and maintain long-term, physiologically-based culture conditions with low fluid shear stress.

Yew, Alvin G.↗
DOE OSTI2020

An Experimental Method to Measure Gaseous Diffusivity in Tight and Partially Saturated Porous Media via Continuously Monitored Mass Spectrometry

Detection of radioxenon and radioargon produced by underground nuclear explosions is one of the primary methods by which the Comprehensive Nuclear-Test–Ban Treaty (CTBT) monitors for nuclear activities. However, transport of these noble gases to the surface via barometric pumping is a complex process relying on advective and diffusive processes in a fractured porous medium to bring detectable levels to the surface. To better understand this process, experimental measurements of noble gas and chemical surrogate diffusivity in relevant lithologies are necessary. However, measurement of noble gas diffusivity in tight or partially saturated porous media is challenging due to the transparent nature of noble gases, the lengthy diffusion times, and difficulty maintaining consistent water saturation. Here, the quasi-steady-state Ney–Armistead method is modified to accommodate continuous gas sampling via effusive flow to a mass spectrometer. An analytical solution accounting for the cumulative sampling losses and induced advective flow is then derived. Experimental results appear in good agreement with the proposed theory, suggesting the presence of retained groundwater reduces the effective diffusivity of the gas tracers by 10–1000 times. Finally, by using a mass spectrometer, the method described herein is applicable to a broad range of gas species and porous media.

47 OTHER INSTRUMENTATION↗
NASA NTRS2007

Isotopic Measurements in CAIs with the Nanosims: Implications to the understanding of the Formation process of Ca, Al-Rich Inclusions

Ca, Al-rich Inclusions (CAIs) preserve evidence of thermal events that they experienced during their formation in the early solar system. Most CAIs from CV and CO chondrites are characterized by large variations in O-isotopic compositions of primary minerals, with spinel, hibonite, and pyroxene being more O-16-rich than melilite and anorthite, with delta 17, O-18 = approx. -40%o (DELTA O-17 = delta O-17 - 0.52 x delta O-18 = approx. - 20%o ). These anomalous compositions cannot be accounted for by standard mass dependent fractionation and diffusive process of those minerals. It requires the presence of an anomalous oxygen reservoir of nucleosynthetic origin or mass independent fractionations before the formation of CAIs in the early solar system. The CAMECA NanoSIMS is a new generation ion microprobe that offers high sensitivity isotopic measurements with sub 100 nm spatial resolution. The NanoSIMS has significantly improved abilities in the study of presolar grains in various kind of meteorites and the decay products of extinct nuclides in ancient solar system matter. This instrument promises significant improvements over other conventional ion probes in the precision isotopic characterization of sub-micron scales. We report the results of our first O isotopic measurements of various CAI minerals from EK1-6-3 and 7R19-1(a) utilizing the JSC NanoSIMS 50L ion microprobe. We evaluate the measurement conditions, the instrumental mass fractionation factor (IMF) for O isotopic measurement and the accuracy of the isotopic ratio through the analysis of a San Carlos olivine standard and CAI sample of 7R19-1(a).

Ito, M.↗
DOE OSTI2021

Estimating viscoelastic compliance of desiccating cementitious materials using drying prism tests

Highlights: • Determining relative humidity and degree of reaction of desiccating cementitious materials via an integrated method • Extracting moisture diffusion coefficient of cement mortar using the mass loss data of the prism specimens • Estimating uniaxial viscoelastic compliance of cement mortar using the shrinkage strain data of the prism specimens An integrated modeling approach to determining internal relative humidity and degree of reaction of desiccating cementitious materials has been developed. By simultaneously accounting for both self-desiccation and external drying, the model is capable of predicting the evolution of material properties of desiccating cementitious materials. Using the mass loss data of the prism specimens, the moisture diffusion coefficient of a nonlinear model for cement mortar was determined. Additionally, a previous poroviscoelastic shrinkage model was modified and extended. Through comparison of predicted and measured axial strain of the prism specimens, the viscoelastic compliance of cement mortar was extracted. The present work revealed that it is possible to use a simple drying prism test to fit the moisture diffusion coefficient and creep compliance of cementitious materials, though the comparison of the extracted viscoelastic compliance with measured compliance was only reasonable if the outer layer of the drying mortar was presumed to have microcracking.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Liquid–Liquid Microfluidic Flows for Ultrafast 5-Hydroxymethyl Furfural Extraction

We study the effects of liquid–liquid flow patterns on the extraction of 5-hydroxymethyl furfural from the aqueous phase into an organic phase (methyl isobutyl ketone, ethyl acetate, and 2-pentanol) at ultrashort residence times of 0.2–20 s in a coiled capillary microchannel. Slug, droplet, slug-droplet, dispersed, parallel, annular, and irregular two-phase flow patterns are generated. We evaluate the extraction efficiency and the volumetric mass transfer coefficient via experiments and computational fluid dynamics (CFD). The CFD predictions are in quantitative agreement with the experimental data. The convective and diffusive contributions to the mass transfer of different flow patterns are analyzed. For all solvent pairs, the extraction efficiency varies irregularly with increasing flow rate due to changes in the mass transfer mechanism caused by a transition between flow regimes. Overall, we demonstrate >90% extraction efficiencies with high volumetric mass transfer coefficients ranging from 0.006 to 2.17 s–1. Furthermore, a merit index is defined to assess the trade-off between the fast mass transfer and the pressure drop in biphasic microchannels. In general, the mass transfer rate increases significantly at high flow rates at the expense of a high-pressure drop. Furthermore, the ethyl acetate/water irregular flow pattern is optimal due to a large throughput, extraction efficiency, and mass transfer coefficient, with a minimal pressure drop.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2025

Temperature dependence of heavy quark diffusion from (2+1)-flavor lattice QCD

We present a lattice determination of the heavy-quark diffusion coefficient in (2+1)-flavor QCD with almost physical quark masses. The momentum and spatial diffusion coefficients are extracted for a wide temperature range, from T = 163 MeV to 10 GeV. The results are in agreement with previous works from the HotQCD collaboration, and show fast thermalization of the heavy quark inside the QGP. Near the chiral crossover temperature T c ≃ 150 MeV, our results are close to the AdS/CFT estimation computed at strong coupling.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2022

Conversion Kinetics and Ionic Conductivity in Na-β”-Alumina + YSZ (Naβ”AY) Sodium Solid Electrolyte via Vapor Phase Conversion Process

Sodium ion batteries have been receiving increasing attention and may see potential revival in the near future, particularly in large-scale grid energy storage coupling with wind and solar power generation, due to the abundant sodium resources, low cost, and sufficiently high energy density. Among the known sodium ion conductors, the Na-β”-alumina electrolyte remains highly attractive because of its high ionic conductivity. This study focuses on the vapor phase synthesis of a Na-β”-Alumina + YSZ (Naβ”AY) composite sodium electrolyte, which has higher mechanical strength and stability than conventional single phase β”-Alumina. The objectives are the measurement of conversion kinetics through a newly developed weight-gain based model and the determination of sodium ionic conductivity in the composite electrolyte. Starting samples contained ~70 vol% α-Alumina and ~30 vol% YSZ (3 mol% Y 2 O 3 stabilized Zirconia) with and without a thin alumina surface layer made by sintering in air at 1600 °C. The sintered samples were placed in a powder of Na-β”-alumina and heat-treated at 1250 °C for various periods. Sample dimensions and weight were measured as a function of heat treatment time. The conversion of α-Alumina in the α-Alumina + YSZ composite into Naβ”AY occurred by coupled diffusion of sodium ions through Na-β”-alumina and of oxygen ions through YSZ, effectively diffusing Na2O. From the analysis of the time dependence of sample mass and dimensions, the effective diffusion coefficient of Na 2 O through the sample, D eff , was estimated to be 1.74 x 10 -7 cm2 s -1 , and the effective interface transfer parameter, k eff , was estimated as 2.33 x 10 -6 cm s -1 . By depositing a thin alumina coating layer on top of the bulk composite, the chemical diffusion coefficient of oxygen through single phase Na-β”-alumina was estimated as 4.35 x 10 -10 cm 2 s -1 . An AC impedance measurement was performed on a fully converted Naβ”AY composite, and the conductivity of the composite electrolyte was 1.3 x 10 -1 S cm -1 at 300 °C and 1.6 x 10 -3 S cm -1 at 25 °C, indicating promising applications in solid state or molten salt batteries at low to intermediate temperatures.

36 MATERIALS SCIENCE↗
NASA NTRS1986

Surface mass transport of alumina

Measurements were made of the kinetics of thermal grooving at the intersection of rhombohedral twin boundaries with the (1 0 -1 0) plane in alumina, at temperatures from 1773 to 2273 K. An analysis of the values obtained on the basis of the model of Mullins (1957) indicated that surface diffusion was the dominant mass transport mechanism. Comparisons are made with the results of other investigations of alumina, and an equation is derived for the surface diffusion value.

Gaddipati, A. R.↗
DOE OSTI2026

Graphene oxide precursor effects on 3D-printed carbon scaffolds

Manganese oxide (MnO 2 ), an earth-abundant material, is a promising component for energy storage devices, with uses in both pseudocapacitors and batteries. However, high MnO 2 loading often leads to reduced performance due to poor ion diffusion. 3D printing, particularly using the direct ink writing (DIW) technique, offers a solution by enabling the fabrication of electrodes with hierarchical porous structures and open channels that enhance mass transport and ion diffusion. Previous work demonstrated that 3D-printed graphene aerogels with MnO 2 coatings exhibited excellent electrochemical performance, even with thick electrodes, due to their optimized structure. Building on this work, the current study investigates the performance differences between aerogels developed using graphene oxide (GO) and reduced graphene oxide (rGO) as carbon precursors. Both materials were incorporated into thixotropic inks, 3D-printed into lattice structures, and carbonized. Despite expected similarities between the final graphene aerogel, rGO-based aerogels exhibited superior areal capacitance, compared to GO-based aerogels. These differences are attributed to the lower oxygen content and defect density of rGO, which influence its interaction with cellulose viscosifiers in the ink formulation. Brunauer–Emmett–Teller (BET) surface area analysis revealed that rGO aerogels exhibit a larger surface area and mesoporous structure, further enhancing their performance. When coated with MnO 2 , rGO-based aerogels maintained their superior capacitive behavior over GO-based aerogels. This study highlights the effect of carbon precursor on the end performance of graphene aerogels.

Materials science↗
NASA NTRS1958

Performance of an All-internal Conical Compression Inlet with Annular Throat Bleed at Mach Number 5.0

An all-internal conical compression inlet with annular bleed at the throat was investigated at Mach 5.0 and zero angle of attack. The minimum contraction ratio of the supersonic diffuser, coincident with a mass-flow ratio of 1.0, was determined to be 0.084 as compared with the isentropic contraction ratio of 0.04 at Mach 5.0. The over-all inlet performance was very sensitive to the amount of annular bleed at the throat because of the extensive boundary layer. For example, the critical recovery varied from 41 percent with 6-percent bleed to 59 percent with 25-percent bleed. Decreasing the spacing between the supersonic and subsonic diffusers increased the critical mass-flow ratio but reduced the range of subcritical mass-flow regulation. A constant-area section was required ahead of the subsonic diffuser in order to obtain reasonable performance. An inlet-engine net-thrust analysis indicated that the optimum performance occurred with from 20- to 25-percent bleed, depending on how the bypassed air was handled.

Stitt, Leonard E.↗
NASA NTRS1975

Viscous-shock-layer solutions with radiation and ablation injection for Jovian entry

This paper presents results that describe the flow field and surface response conditions for a planetary probe entering the atmosphere of Jupiter. The results are obtained with a viscous-shock-layer analysis which includes mass injection, radiative transfer, diffusion, and viscous effects. Radiative transfer is calculated with an existing nongray radiation model that accounts for molecular band, atomic line, and continuum transitions. Particular emphasis is given to the effect of mass injection on the stagnation and downstream flow. Results for both specified and coupled mass injection are obtained for a carbon heat shield.

Moss, J. N.↗
NASA NTRS1990

Drop evaporation in a single-axis acoustic levitator

A 20 kHz single-axis acoustic positioner is used to levitate aqueous-solution drops (volumes less than or approximately equal to 100 micro-liters). Drop evaporation rates are measured under ambient, isothermal conditions for different relative humidities. Acoustic convection around the levitated sample enhances the mass loss over that due to natural convection and diffusion. A theoretical treatment of the mass flow is developed in analogy to previous studies of the heat transfer from a sphere in an acoustic field. Predictions of the enhanced mass loss, in the form of Nusselt (Sherwood) numbers, are compared with observed rages of drop shrinking. The work is part of an ESA crystal growth from levitated solution drops.

Lierke, E. G.↗