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Results for “Kinetic Modelling”

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 1,171 records · Page 65
All sourcesNASA NTRSDOE OSTI
DOE OSTI2018

Simulation of the Dynamics of Isothermal Growth of Single-Layer Graphene on a Copper Catalyst in the Process of Chemical Vapor Deposition of Hydrocarbons

A new kinetic model of isothermal growth of single-layer graphene on a copper catalyst as a result of the chemical vapor deposition of hydrocarbons on it at a low pressure has been developed on the basis of in situ measurements of the growth of graphene in the process of its synthesis. This model defines the synthesis of graphene with regard for the chemisorption and catalytic decomposition of ethylene on the surface of a copper catalyst, the diffusion of carbon atoms in the radial direction to the nucleation centers within the thin melted near-surface copper layer, and the nucleation and autocatalytic growth of graphene domains. It is shown that the time dependence of the rate of growth of a graphene domain has a characteristic asymmetrical bell-like shape. The dependences of the surface area and size of a graphene domain and the rate of its growth on the time at different synthesis temperatures and ethylene concentrations have been obtained. Time characteristics of the growth of graphene domains depending on the parameters of their synthesis were calculated. The results obtained can be used for determining optimum regimes of synthesis of graphene in the process of chemical vapor deposition of hydrocarbons on different catalysts with a low solubility of carbon.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2018

Kinetic Simulation of Collisional Magnetized Plasmas with Semi-implicit Time Integration

Plasmas with varying collisionalities occur in many applications, such as tokamak edge regions, where the flows are characterized by significant variations in density and temperature. While a kinetic model is necessary for weakly-collisional high-temperature plasmas, high collisionality in colder regions render the equations numerically stiff due to disparate time scales. In this study, we propose an implicit–explicit algorithm for such cases, where the collisional term is integrated implicitly in time, while the advective term is integrated explicitly in time, thus allowing time step sizes that are comparable to the advective time scales. This partitioning results in a more efficient algorithm than those using explicit time integrators, where the time step sizes are constrained by the stiff collisional time scales. Finally, we implement semi-implicit additive Runge–Kutta methods in COGENT, a high-order finite-volume gyrokinetic code and test the accuracy, convergence, and computational cost of these semi-implicit methods for test cases with highly-collisional plasmas.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2018

Crosslinked Polyacrylamide Composite Hydrogels Impregnated with Fly Ash: Synthesis, Characterization and Their Application as Fractures Sealant for High Water Producing Zones in Oil and Gas Wells

Polymeric hydrogels are designed to serve many purposes in various fields of human endeavor. Herein, crosslinked polyacrylamide (PAM) composite hydrogels impregnated with coal fly ash (CFA) were synthesized, characterized and tested as fracture sealing agents in high water producing permeable zones in petroleum industry. The concept of utilizing CFA as an inorganic additive in the matrix of hydrogel emanates from the fact that CFA constitutes majorly alumina and silica. Both chemical oxides can induce the CFA to promote the inherent properties of hydrogel. Polyethyleneimine (PEI) was chosen as the crosslinking agent. Neat PAM/PEI hydrogel and PAM/PEI–CFA hydrogels at various CFA loadings (0.5, 1 and 2 wt%) were synthesized via a transamidation reaction pathway. The developed hydrogels were characterized by hybrid rheometer, FTIR, SEM and XRD instruments. Rheological results reveal that the PAM/PEI–CFA composite hydrogels embedded with various CFA quantities were more elastic than the neat PAM/PEI hydrogel, indicating the dispersion and reinforcing effect of CFA. The functional groups of these hydrogels were confirmed by the FTIR while SEM analysis show that the surface micrographs of neat PAM/PEI hydrogel and PAM/PEI–CFA1 hydrogel were porous in several regions. In contrast, the micrographs of PAM/PEI–CFA2 and PAM/PEI–CFA3 hydrogels demonstrated dense and “net-like” structural patterns. Further, XRD analysis revealed that CFA impregnation has a significant effect on the bulk structural properties of the fabricated hydrogels. The swelling rates of these hydrogels were determined by the gravimetric method and their diffusion parameters evaluated using Fickian diffusion and Schott-order kinetic models. Efficacy of the PAM/PEI–CFA composite hydrogel as fractures sealant in oil and gas wells was conducted at a typical reservoir temperature, 90 °C, and the outcome demonstrated considerable sealing potency.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Use of Isolated Pectin from a Cissampelos pareira-Based Polymer Blend Matrix for the Transdermal Delivery of Nicotine

Pectin is a natural biopolymer, and a major component of a complex heterogeneous polysaccharide found in the primary cell walls and middle lamella of plant tissues. This paper used pectin isolated from Cissampelos pareira (Krueo Ma Noy) leaves to prepare the matrix layer for nicotine transdermal patches. However, the patch was a brittle film, thus, deproteinized natural rubber latex (DNRL) was blended to improve flexibility of the patch. Here we present for the first time a preparation study exploring the suitability of isolated pectin blends to serve as drug carriers and the mechanism controlling the release patterns of nicotine. The hydrophilicity of the patches was found to decrease when increasing the DNRL ratio. Differential scanning calorimetry and X-ray diffraction experiments were used to characterize the interactions between the investigated drugs and the matrix polymers. In vitro studies showed that the isolated pectin blends were an effective matrix for controlled nicotine release. The release and permeation patterns of nicotine depend on the hydrophilicity of the patches. The kinetic models of nicotine were found to be a Higuchi model and zero order for in vitro release and skin permeation, respectively.

38 RADIATION CHEMISTRY, RADIOCHEMISTRY, AND NUCLEA↗
DOE OSTI2019

Application of Novel Adsorbent Prepared by Mucor hiemalis Biomass Impregnated with Calcium Alginate for Removal of Sr{sup 2+} from Aqueous Solutions

In this research, a novel biosorbent was prepared by Mucor hiemalis biomass combined with calcium alginate (Mucor hiemalis/Alg-Ca). The dead biomass was entrapped into alginate gel by curing method in the presence of Ca{sup 2+} ions. The synthesized biosorbent characterized by XRD, EDAX, BET, FTIR, and SEM techniques was used for removal of Sr{sup 2+} from aquatic streams under various experimental conditions and the optimized adsorption capacity of 140 mg g{sup −1} was obtained. The selectivity of the adsorbent towards Sr{sup 2+} studied in the presence of Na{sup +}, Cs{sup +}, Ca{sup 2+} and Mg{sup 2+} was reasonably high. The adsorption process was kinetically fast and the equilibrium was established within 60 min, and followed the pseudo-second order kinetics model. The equilibrium data was well described by Langmuir isotherm model. The thermodynamics parameters (∆G°, ∆H° and ∆S°) of the process were determined. Positive ∆H° and negative ∆G° were indicative of the endothermic and spontaneous nature of the adsorption process. Graphical Abstract: .

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2019

Magnetic Nanoparticles Impregnated, Cross-Linked, Porous Chitosan Microspheres for Efficient Adsorption of Methylene Blue from Pharmaceutical Waste Water

The study demonstrates the preparation of MnFe{sub 2}O{sub 4} impregnated chitosan-microspheres (CMMS) as adsorbents for efficient removal of cationic thiazine dye, methylene blue. A facile approach with great economic and technical advantages to obtain highly crystalline manganese ferrite nanoparticles by solution combustion method is accounted. CMMS were characterized and evaluated for MB adsorption using linear forms of Freundlich and Langmuir adsorption isotherms, pseudo-first order, pseudo-second order and Elovich kinetic models. Application of CMMS to pharmaceutical waste, desorption of MB and reusability of CMMS are reported. Significantly, MB concentration in treated real sample was reduced by ~ 18 times to that of initial concentration. Graphic Abstract: .

36 MATERIALS SCIENCE↗
DOE OSTI2025

Nonpigmented PsbR is involved in the integrity of excitation landscape in higher plant photosystem II, a case study in Arabidopsis thaliana and a mutant

PsbR is a nonpigmented 10 kDa protein in Photosystem II (PSII) in algae and plants. A recent structural study clarified its enigmatic structural location in a Photosystem II megacomplex that has baffled the community for more than four decades. Our current study interrogates whether absence of PsbR affects the overall dynamics of excitation energy migration within light harvesting complexes (LHC) and PSII super assemblies using highly-active PSII membrane particles, so-called BBY particles, isolated from a PsbR deletion mutant (ΔPsbR) of Arabidopsis thaliana. A femto-second (fs)-time-resolved transient absorption experimentation recorded at 77 K with selective excitation of Chl b which is exclusively present in LHCs enabled us to resolve the temporal differences in LHC→LHC and LHC→PSII excitation energy transfer steps. By applying specific target spectro-kinetic models to the transient absorption datasets, we demonstrated that the time constants of Chl a LHC → Chl a LHC excitation transfer significantly elongates in the ΔPsbR LHC-PSII particles, suggestive of the decreased aggregation level of photosynthetic proteins in the mutant. These findings highlight excitation energy transfer integrity in LHC-PSII assembly is not only determined by the pigmented light-harvesting complexes, but also synergistically by the nonpigmented PSII components. Furthermore, the disturbed integrity in dynamics of excitation energy transfer pathway within LHC-PSII supercomplex is discussed in the context of the altered LHC-PSII megacomplexes type I and II architectures which result from the absence of the PsbR protein in higher plant PSII.

Chlorophyll↗
DOE OSTI2020

Extracting meaningful standard enthalpies and entropies of activation for surface reactions from kinetic rates

While analyses based on the Arrhenius kinetic model have been successfully applied since its introduction, the Arrhenius model neglects to describe pre-exponential factor in a scientifically meaningful fashion. Since the 1930s, transition-state theory (TST), has met with success in interpreting the pre-exponential factor’s value, allowing a standard entropy of activation to be estimated. However, analyses based on TST’s assumptions have been applied inconsistently in the literature, particularly in corrosion science, leading to difficulty in comparison of standard entropy of activations from different studies. In this work, the foundational principles of TST and standard states are discussed and a standard method to apply TST in analyzing rates of surface reactions is recommended. When full details are not available, reacting species’ concentrations should be normalized to the concentration of active surface sites. For corrosion reactions, conversion relationships are given to convert from units of corrosion rate to surface reaction rate, consistent with TST. This method is dubbed a surface reactant equi-density approximation. Application of this standard to reported data results in adjustments of the standard entropy of activation between - 65 and +50 J/mol K and brings reported entropies into a narrower range of values.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2019

Characterizing the Effect of Thermal Processing on Feedstock Al Alloy Powder for Additive Manufacturing Applications

Gas-atomized metallic powders are commonly used in additive manufacturing processes. Research has shown that, for certain AM techniques, the chemistry and microstructural properties of the feedstock powders significantly affect the properties of the consolidated material. Understanding the powder characteristics before use in additive manufacturing can lead to optimizing properties of additively manufactured materials as well as determining the recyclability of feedstock powders. This research studies the effect of various solution treatment processes on the characteristics and microstructural evolution of powder aluminum alloy 6061. Solution treatment times and temperatures were guided by thermodynamic and kinetic modeling. Light microscopy, scanning electron microscopy, and hardness were used to evaluate each condition in both two and three dimensions. Results indicate that the Mg{sub 2}Si present in the untreated condition dissolves after 60 min of solution treatment, while there are competing effects from the dissolution and concurrent growth of various Fe-containing phases. Additionally, it is shown that both granular and sub-granular structures exist in these rapidly solidified powders, and the sub-grains reorient themselves during solution treatment.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Experimental Study on the Hot Deformation Characterization of Low-Carbon Nb-V-Ti Microalloyed Steel

X80 steel, as typical low-carbon Nb-V-Ti microalloyed steel, is getting more and more attention in oil and gas transmission pipeline manufacturing. In this paper, the hot deformation behavior of X80 steel has been investigated. Hot compression tests of the steel were conducted under different temperatures and strain rates. Based on the experimental data, the flow stress constitutive equations were established. It is found that the hot deformation activation energy of this steel is higher than C-Mn and low-carbon steel. Then, the kinetics model and grain size model of dynamic recrystallization were developed according to the flow curves and the optical microstructures. In addition, the processing maps were developed to analyze the workability of X80 steel at elevated temperature. The analysis results show that the optimum processing window is at the temperature of 1300-1473 K and the strain rate of 0.01-10 s{sup −1}. The microstructure observation indicates that the optimum processing parameters are applicable to the tested steel.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Improvement of Sugarcane Stillage (Vinasse) Anaerobic Digestion with Cheese Whey as its Co-substrate: Achieving High Methane Productivity and Yield

This study investigated methane production in an anaerobic sequencing batch biofilm reactor (AnSBBR) by co-digesting sugarcane vinasse and cheese whey. The assessment was based on the influence of feed strategy, interaction between cycle time and influent concentration, applied volumetric organic load (OLR{sub A}), and temperature over system stability and performance. The system showed flexibility with regard to the feed strategy, but the reduction of cycle time and influent concentration, at the same OLR{sub A}, resulted in lower methane productivity. Increasing organic load, up to the value of 15.27 gCOD L{sup −1} day{sup −1}, favored the process, increasing methane yield and productivity. Temperature reduction from 30 to 25 °C resulted in worse performance, although increasing it to 35 °C provided similar results to 30 °C. The best results were achieved at an OLR{sub A} of 15.27 gCOD L{sup −1} day{sup −1}, cycle time of 8 h, fed-batch operation, and temperature of 30 °C. The system achieved soluble COD removal efficiency of 89%, methane productivity of 208.5 molCH{sub 4} m{sup −3} day{sup −1} and yield of 15.76 mmolCH{sub 4} gCOD{sup −1}. The kinetic model fit indicated methanogenesis preference for the hydrogenotrophic route. At the industrial scale estimative, considering a scenario with a sugarcane ethanol plant with ethanol production of 150,896 m{sup 3} year{sup −1}, it was estimated energy production of 25,544 MWh month{sup −1}.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2017

Avoiding full corrections in dynamic SPECT images impacts the performance of SPECT myocardial blood flow quantitation

Introduction: This study investigated the performance of SPECT myocardial blood flow (MBF) quantitation lacking full physical corrections (All Corr) in dynamic SPECT (DySPECT) images. Methods: Eleven healthy normal volunteers (HVT) and twenty-four patients with angiography-documented CAD were assessed. All Corr in {sup 99m}Tc-sestamibi DySPECT encompassed noise reduction (NR), resolution recovery (RR), and corrections for scatter (SC) and attenuation (AC), otherwise no correction (NC) or only partial corrections. The performance was evaluated by quality index (R{sup 2}) and blood-pool spillover index (FBV) in kinetic modeling, and by rest flow (RMBF) and stress flow (SMBF) compared with those of All Corr. Results: In HVT group, NC diminished 2-fold flow uniformity with the most degraded quality (15%-18% reduced R{sup 2}) and elevated spillover effect (45%-50% increased FBV). Consistently higher RMBF and SMBF were discovered in both groups (HVT 1.54/2.31 higher; CAD 1.60/1.72; all P < .0001). Bland-Altman analysis revealed positive flow bias (HVT 0.9-2.6 mL/min/g; CAD 0.7-1.3) with wide ranges of 95% CI of agreement (HVT NC −1.9-7.1; NR −0.4-4.4; NR + SC −1.1-4.3; NR + SC + RR −0.7-2.5) (CAD NC −1.2-3.8; NR −1.0-2.8; NR + SC −1.0-2.5; NR + SC + RR −1.1-2.6). Conclusions: Uncorrected physical interference in DySPECT images can extensively impact the performance of MBF quantitation. Full physical corrections should be considered to warrant this tool for clinical utilization.

62 RADIOLOGY AND NUCLEAR MEDICINE↗
DOE OSTI2018

Ion Mobility Spectrometry-Mass Spectrometry Coupled with Gas-Phase Hydrogen/Deuterium Exchange for Metabolomics Analyses

Ion mobility spectrometry-mass spectrometry (IMS-MS) in combination with gas-phase hydrogen/deuterium exchange (HDX) and collision-induced dissociation (CID) is evaluated as an analytical method for small-molecule standard and mixture characterization. Experiments show that compound ions exhibit unique HDX reactivities that can be used to distinguish different species. Additionally, it is shown that gas-phase HDX kinetics can be exploited to provide even further distinguishing capabilities by using different partial pressures of reagent gas. The relative HDX reactivity of a wide variety of molecules is discussed in light of the various molecular structures. Additionally, hydrogen accessibility scoring (HAS) and HDX kinetics modeling of candidate (in silico) ion structures is utilized to estimate the relative ion conformer populations giving rise to specific HDX behavior. These data interpretation methods are discussed with a focus on developing predictive tools for HDX behavior. Finally, an example is provided in which ion mobility information is supplemented with HDX reactivity data to aid identification efforts of compounds in a metabolite extract. .

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

Vacancy diffusion barrier spectrum and diffusion correlation in multicomponent alloys

Vacancy diffusion serves a crucial role in many important kinetic behaviors and properties of multicomponent alloys. Essential questions, however, persist regarding how chemical complexity affects diffusion and what unique characteristics, if any, set these alloys apart from traditional metals. Using neural network kinetics model, we study vacancy diffusion in NbMoTa alloy across a broad temperature range (2600 to 800 K). Unlike pure metals, the two key diffusion parameters—diffusion correlation factor f and activation energy ΔG m —are not constant in alloys, but instead substantially decrease with decreasing temperature. This temperature dependence arises from a reduced number of active vacancy jump pathways at lower temperatures, leading to more correlated diffusion. Upon examining vacancy diffusion throughout the entire compositional space of the Nb-Mo-Ta system, we discover that the slowest vacancy diffusion surprisingly occurs in the non-equimolar region, rather than the equimolar concentration where the configurational entropy is highest. The diffusion barrier spectrum, characterizing the diffusion energy landscape, is an intrinsic material characteristic, which controls both f and ΔG m and, thereby, the diffusivity. Lastly, we find that the vacancy diffusion rate drops noticeably in the presence of local chemical order in the NbMoTa system, particularly for MoTa alloys with long-range B2 order.

Defects↗
DOE OSTI2022

On the various Cu-redox pathways and O 2 -mediated Bronsted-to-Lewis adsorbed-NH 3 redistribution under SCR half-cycle conditions

The Standard SCR reaction on Cu-SSZ-13 is a complex redox process facilitated by a reduction half cycle (RHC) and an oxidation half cycle (OHC). It is generally accepted that RHC requires the simultaneous presence of NO and NH 3 , while OHC requires both NO and O 2 ; however understanding of how these individual reactants impact the Cu redox cycle is limited. In this work, we provide experimental investigation of NO-only, NH 3 -only and NO+NH 3 RHC, and their relative rates. Simple kinetic models were developed to understand the dependance of NO-only and NH 3 -only RHC on Cu speciation. Various OHC routes including NO+O 2 and O 2 -only OHC, and a previously unreported H 2 O-mediated OHC pathway were also investigated. Detailed NH 3 temperature-programmed desorption studies showed that RHC selectively consumes NH 3 adsorbed on Lewis-acid sites, and that part of the remaining Bronsted-bound NH 3 moves to the Lewis-acid sites during subsequent OHC, thereby resulting in a repartitioning of adsorbed NH 3 .

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2018

Biochemical Production with Purified Cell-Free Systems

Bioprocesses offer a powerful set of opportunities for current chemical process innovation. Such conversions provide opportunities to employ process intensification strategies and the right characteristics to scale down and harness the power of modular process design, but strain engineering and the use of microbial systems for industrial biochemicals production remain unpredictable and expensive. Purified cell-free technologies, in which complex enzyme reaction cascades are used to catalyze bioconversions of interest, can be designed to mitigate these limitations. Such systems allow predictive kinetic modeling and full control of reaction conductions, enabling a dramatically increased design-built-test cycle iteration rate. When sufficiently robust engineered enzymes are used, opportunities to leverage harsh reaction conditions, long-term recycling strategies, and hybridization with chemical catalysis can be used to dramatically improve the value proposition of biochemicals production. As a result, further research is required to realize the potential of these approaches and to address the current platform-limiting challenges around cofactor cost and reuse.

09 BIOMASS FUELS↗