Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “Kinetics”

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.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 811 records · Page 45
All sourcesNASA NTRSDOE OSTI
NASA NTRS1999

Kinetics of template-directed pyrophosphate-linked dideoxyguanylate synthesis as a function of 2-MeImpdG and poly(C) concentration: insights into the mechanism

Aqueous solutions of deoxyguanosine 5'-monophosphate 2-methylimidazolide, 2-MeImpdG, yield primarily deoxyguanosine 5'-monophosphate, 5'dGMP, and pyrophosphate-linked dideoxyguanylate, dG5'ppdG, abbreviated G2p (see Chart 1). The initial rate of G2p formation, d[G2p]/dt in M h-1, determined at 23 degrees C, pH 7.8, 1.0 M NaCl and 0.2 M Mg2+ by timed high-performance liquid chromatography (HPLC) analysis, exhibits a second-order dependence on 2-MeImpdG concentration, [G]o, indicating a bimolecular mechanism of dimerization in the range 0.02 M < or = [G]o < or = 0.09 M. In the presence of polycytidylate, poly(C), G2p synthesis is accelerated and oligodeoxyguanylate products are formed by incorporation of 2-MeImpdG molecules. The kinetics of G2p formation as a function of both monomer and polymer concentration, expressed in C equivalents, were also determined under the above conditions and exhibited a complex behavior. Specifically, at a constant [poly(C)], values of d[G2p]/dt typically increased with [G]o with a parabolic upward curvature. At a constant [G]o, values of d[G2p]/dt increase with [poly(C)], but level off at the higher poly(C) concentrations. As [G]o increases this saturation occurs at a higher poly(C) concentration, a result opposite to expectation for a simple complexation of two reacting monomers with the catalyst prior to reaction. Nevertheless, these results are shown to be quantitatively consistent with a template-directed (TD) mechanism of dimerization where poly(C) acts as the template to bind 2-MeImpdG in a cooperative manner and lead, for the first time, to the formulation of principles that govern template-directed chemistry. Analysis of the kinetic data via a proposed TD cooperative model provides association constants for the affinity between polymer and monomer and the intrinsic reactivity of 2-MeImpdG toward pyrophosphate synthesis. To the best of our knowledge, poly(C)/2-MeImpdG is the first system that could serve as a textbook example of a TD reaction under conditions such that the template is fully saturated by monomers and under conditions that it is not.

NASA Discipline Exobiology↗
NASA NTRS1999

Sequential and coordinated action of phytochromes A and B during Arabidopsis stem growth revealed by kinetic analysis

Photoreceptor proteins of the phytochrome family mediate light-induced inhibition of stem (hypocotyl) elongation during the development of photoautotrophy in seedlings. Analyses of overt mutant phenotypes have established the importance of phytochromes A and B (phyA and phyB) in this developmental process, but kinetic information that would augment emerging molecular models of phytochrome signal transduction is absent. We have addressed this deficiency by genetically dissecting phytochrome-response kinetics, after having solved the technical issues that previously limited growth studies of small Arabidopsis seedlings. We show here, with resolution on the order of minutes, that phyA initiated hypocotyl growth inhibition upon the onset of continuous red light. This primary contribution of phyA began to decrease after 3 hr of irradiation, the same time at which immunochemically detectable phyA disappeared and an exclusively phyB-dependent phase of inhibition began. The sequential and coordinated actions of phyA and phyB in red light were not observed in far-red light, which inhibited growth persistently through an exclusively phyA-mediated pathway.

NASA Discipline Plant Biology↗
NASA NTRS1997

A model for the kinetics of homotypic cellular aggregation under static conditions

We present the formulation and testing of a mathematical model for the kinetics of homotypic cellular aggregation. The model considers cellular aggregation under no-flow conditions as a two-step process. Individual cells and cell aggregates 1) move on the tissue culture surface and 2) collide with other cells (or aggregates). These collisions lead to the formation of intercellular bonds. The aggregation kinetics are described by a system of coupled, nonlinear ordinary differential equations, and the collision frequency kernel is derived by extending Smoluchowski's colloidal flocculation theory to cell migration and aggregation on a two-dimensional surface. Our results indicate that aggregation rates strongly depend upon the motility of cells and cell aggregates, the frequency of cell-cell collisions, and the strength of intercellular bonds. Model predictions agree well with data from homotypic lymphocyte aggregation experiments using Jurkat cells activated by 33B6, an antibody to the beta 1 integrin. Since cell migration speeds and all the other model parameters can be independently measured, the aggregation model provides a quantitative methodology by which we can accurately evaluate the adhesivity and aggregation behavior of cells.

Non-NASA Center↗
NASA NTRS2013

Mission Opportunities for the Flight Validation of the Kinetic Impactor Concept for Asteroid Deflection

The kinetic impactor technique for deflecting near-Earth objects (NEOs), whereby a spacecraft is directed to collide with a NEO to alter its orbit via momentum transfer, is one of several proposed methods for defendingEarth against hazardous NEOs (asteroids and comets). In this paper we present detailed mission design concepts for a notionally feasible and aff ordable kinetic impactor flight validation mission deployed to a currently known near-Earth asteroid (NEA). Several filter steps are devised that utilize relevant criteria to optimally balance keyparameters, such as approach phase angle, estimated NEA diameter, relative velocity at intercept, and current NEA orbit knowledge, and produce refined lists of the most promising candidate target NEAs.

mission design↗
NASA NTRS2017

Wave-Particle Energy Exchange Directly Observed in a Kinetic Alfven-Branch Wave

Alfven waves are fundamental plasma wave modes that permeate the universe. At small kinetic scales they provide a critical mechanism for the transfer of energy between electromagnetic fields and charged particles. These waves are important not only in planetary magnetospheres, heliospheres, and astrophysical systems, but also in laboratory plasma experiments and fusion reactors. Through measurement of charged particles and electromagnetic fields with NASAs Magnetospheric Multiscale (MMS) mission, we utilize Earths magnetosphere as a plasma physics laboratory. Here we confirm the conservative energy exchange between the electromagnetic field fluctuations and the charged particles that comprise an undamped kinetic Alfven wave. Electrons confined between adjacent wave peaks may have contributed to saturation of damping effects via non-linear particle trapping. The investigation of these detailed wave dynamics has been unexplored territory in experimental plasma physics and is only recently enabled by high-resolution MMS observations.

magnetohydrodynamic↗
NASA NTRS2020

Structural evolution, electrochemical kinetic properties, and stability of A-site doped perovskite Sr(1-x)Yb(x)CoO(3-δ)

Mixed ionic and electronic conducting (MIEC) perovskite SrCoO(3-δ) is a widely studied (electro)catalyst for the oxygen reduction reaction (ORR) and possesses different crystal structures at different temperatures. These temperature dependent phase transitions significantly impact the ordering of oxygen vacancies and electrochemical kinetic properties as well as the reliability of the related devices. Some of the crystal structures formed, e.g. hexagonal phases, turn out to be almost impermeable to oxygen gas. Therefore, it is important to stabilize the crystal structure of SrCoO(3-δ) that favors the ORR over a wide temperature range. Herein, the partial substitution of the A-site Sr with Yb is systematically studied, including synthesis, characterization and analysis of structural evolution, electrochemical kinetic properties, thermal stability, and stability in a CO2-containing atmosphere. The results indicate that Sr(0.90)Yb(0.10)CoO(3-δ) is able to stabilize the tetragonal crystal structure with less ordered oxygen vacancies, leading to polarization resistances of 0.051, 0.115 and 0.272 U sq.cm at 750, 700 and 650 °C, respectively, on symmetrical cells. Sr(0.90)Yb(0.10)CoO(3-δ) demonstrates a very stable surface oxygen vacancy distribution and electronic structure near oxygen vacancies but dissociation of adsorbed oxygen molecules into atomic oxygen is affected by surface Sr segregation, and polarization resistance degradation is mainly induced by surface Sr segregation. Furthermore, Sr(0.90)Yb(0.10)CoO(3-δ) exhibits excellent thermal stability as well as excellent recovery stability and improved polarization performance after a few pure air/CO2-containing air treatment cycles at 700 °C. However, a hysteresis behavior of polarization performance is observed at 650 °C during gas cycling treatment, which may cause long-term degradation of the Sr(0.90)Yb(0.10)CoO(3-δ) electrode. The different polarization behaviors during gas cycling treatment are induced by different sensitivities of the formed surface strontium carbonate and chemisorbed surface oxo-carbonaceous species to different operating temperatures.

electrochemical kinetic↗
DOE OSTI2022

Modeling Heat Transfer and Reaction Kinetics of Biomass in Pyrolysis Feeding Systems

Biomass feedstocks can be used to produce low carbon-intensity chemicals and liquid fuels by displacing fossil-fuel sources. Pyrolysis is the thermal decomposition of biomass in the absence of oxygen and can be used to produce crude biofuels. A typical feeding mechanism for pyrolysis reactors is by lock hopper followed by a horizontal auger feeder. Particle agglomeration and plugging of the auger screw are regularly occurring phenomena that is detrimental to the process since it results in the need for periodic inspection and cleaning. The underlying mechanisms leading to agglomeration and plugging are unclear, but a working hypothesis is that heat from the reactor raises the temperature of the biomass in the feeder to the point at which preliminary decomposition reactions occur and produce "sticky" products. Using principles of heat and mass transfer, we derived one-dimensional differential equations for heat flow from the pyrolysis reactor through the auger feeder. Temperature profiles were solved from the system of one-dimensional differential equations using the shooting method. Subsequently, we used the temperature profiles as a one-way coupling to a reaction model for the biomass in the feeder. Kinetic models were adopted from the literature and used to predict the formation of intermediates, products, char, extractives, and metaplastics as well as phase changes along the auger feeder. Species were identified that correlated with softening of the biomass, causing it to become sticky and plug the feeder. We will discuss the details of this work, our findings, and the direction of future work that includes fully coupled transport and reaction-kinetics simulations.

BIOMASS FUELS↗
DOE OSTI2025

A Semi-Detailed Pyrolytic Gas-Phase Kinetic Model for the Volatiles of Polyethylene Thermal Degradation

This work presents a semi-detailed kinetic model to address the pyrolytic gas-phase reactivity of volatiles formed during thermal degradation of polyethylene (PE). The model builds on a validated multi-step condensed-phase model and employs validated lumping approaches. Short-chain compounds are modelled with high detail, while long-chain ones are described by surrogate species representative of diesel-cuts (NC16H32) and waxes (NC30H60). The reactivity of short chains is described through the comprehensive CRECK kinetic model, updated to align C5-C7 olefins based on recent literature experimental data. Due to the lack of experimental data for longer olefins, their reactivity is modeled by analogy to the shorter ones, ensuring an asymptotic behavior with increasing carbon numbers. The semi-detailed model is validated through experimental data on PE pyrolysis, assuming an instantaneous mixing of the inert inlet flow with released volatiles, followed by a segregated plug-flow behavior. Validation across different reactor setups confirms the model’s capability to predict detailed product distributions. Despite minor discrepancies, the proposed model effectively captures experimental trends. Further work will address modelling the reactivity in oxygen-containing environments.

kinetics↗
DOE OSTI2021

Solvent Impregnated Polymers Loaded with Liquid-Like Nanoparticle Organic Hybrid Materials for Enhanced Kinetics of Direct Air Capture and Point Source CO 2 Capture

Hybrid CO 2 capture materials, solvent impregnated polymers (SIPs), are developed based on a simple and scalable encapsulation technique to enhance CO 2 capture kinetics of water-lean solvents with high viscosity. Liquid-like nanoparticle organic hybrid materials functionalized with polyethylenimine (NOHM-I-PEI) are incorporated into a shell material and UV-cured to produce gas-permeable solid sorbents with uniform NOHMs loading (NPEI-SIPs). The CO 2 capture kinetics of NPEI-SIPs show a remarkable 50-fold increase compared to that of neat NOHM-I-PEI due to a large increase in the NOHMs-CO 2 interfacial surface area provided by the SIP design. The optimum NOHM-I-PEI loading and sorption temperature are found to be ≈49 wt% and 50 °C, respectively, and NPEI-SIPs exhibit great thermal stability over 20 CO 2 capture/sorbent regeneration temperature swing cycles. The pseudoequilibrium CO 2 loadings of NPEI-SIPs under humid conditions are as high as 3.1 mmol CO 2 g -1 NPEI - SIPs for 15 vol% CO 2 (postcombustion capture) and 1.7 mmol CO 2 g -1 NPEI - SIPs for 400 ppm (direct air capture). Overall, these findings suggest that NPEI-SIPs can effectively capture CO 2 from a wide range of CO 2 concentrations including direct air capture while allowing the flexible design of CO 2 capture reactors by combining the benefits of liquid solvents and solid sorbents.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Phloroglucinol–2,6‐Diaminoanthraquinone as a Durable Redox Mediator for Enhancing Conversion Reaction Kinetics in Lithium‐Sulfur Batteries

Abstract Lithium‐sulfur batteries, despite being a promising solution for next‐generation secondary batteries, require substantial efforts to overcome the challenges of sluggish sulfur redox kinetics, polysulfides shuttling, and Li metal instability before achieving practical viability. Conventional strategies that utilize metal catalysts or soluble redox mediators (RMs) are limited by either impractical producing processes or unsatisfactory service life. Herein, an electrochemically active organic material, phloroglucinol – 2,6‐diaminoanthraquinone (PG‐DAAQ) is synthesized through a green and facile polymerization process to better resolve these issues. Serving as an RM at the cathode, PG‐DAAQ exhibits enduring redox activity within the sulfur operating potential window, leading to enhanced redox kinetics and sulfur utilization. Remarkably, even without any metal elements, PG‐DAAQ exhibits an excellent affinity to polysulfides, thereby suppressing the shuttling and facilitating the formation of a more favorable solid‐electrolyte interface to stabilize Li deposition at the anode. As a result, Li‐S cells employing PG‐DAAQ show significantly enhanced cycling and rate performances than the control cells. Even with a low electrolyte‐to‐sulfur ratio of 6, pouch cells with PG‐DAAQ deliver a reversible discharge capacity of 821 mA h g −1 after 100 cycles at a C/10 rate.

Lai, Tianxing↗
DOE OSTI2020

Achieving Balanced Crystallization Kinetics of Donor and Acceptor by Sequential-Blade Coated Double Bulk Heterojunction Organic Solar Cells

Sequential deposition has great potential to achieve high performance in organic solar cells due to the resulting well-controlled vertical phase separation. In this work, double bulk heterojunction organic solar cells are fabricated by sequential-blade cast in ambient conditions. Probed by the in situ grazing incidence X-ray diffraction and in situ UV–vis absorption measurements, the seq-blade system exhibits a different tendency from each of the binary films during the film formation process. Due to the extensive aggregation of FOIC, the binary PBDB-T:FOIC film displays a strong and large phase separation, resulting in low current density (J sc) and unsatisfactory power conversion efficiency. In the seq-blade cast system, the bottom layer PBDB-T:IT-M produces many crystal nuclei for the top layer PBDB-T:FOIC, so the PBDB-T molecules are able to crystallize easily and quickly. Balanced crystallization kinetics between polymer and small molecule and an ideal percolation network in the film are observed. In addition, the balanced crystallization kinetics are favorable toward realizing lower recombination loss through charge transport processes.

14 SOLAR ENERGY↗
DOE OSTI2020

Beyond the Polysulfide Shuttle and Lithium Dendrite Formation: Addressing the Sluggish Sulfur Redox Kinetics for Practical High‐Energy Li‐S Batteries

Abstract Electrolyte modulation simultaneously suppresses polysulfide the shuttle effect and lithium dendrite formation of lithium–sulfur (Li‐S) batteries. However, the sluggish S redox kinetics, especially under high S loading and lean electrolyte operation, has been ignored, which dramatically limits the cycle life and energy density of practical Li‐S pouch cells. Herein, we demonstrate that a rational combination of selenium doping, core–shell hollow host structure, and fluorinated ether electrolytes enables ultrastable Li stripping/plating and essentially no polysulfide shuttle as well as fast redox kinetics. Thus, high areal capacity (>4 mAh cm −2 ) with excellent cycle stability and Coulombic efficiency were both demonstrated in Li metal anode and thick S cathode (4.5 mg cm −2 ) with a low electrolyte/sulfur ratio (10 μL mg −1 ). This research further demonstrates a durable Li‐Se/S pouch cell with high specific capacity, validating the potential practical applications.

Zhao, Chen↗
DOE OSTI2020

Beyond the Polysulfide Shuttle and Lithium Dendrite Formation: Addressing the Sluggish Sulfur Redox Kinetics for Practical High-Energy Li-S Batteries

Electrolyte modulation simultaneously suppresses polysulfide the shuttle effect and lithium dendrite formation of lithium-sulfur (Li-S) batteries. However, the sluggish S redox kinetics, especially under high S loading and lean electrolyte operation, has been ignored, which dramatically limits the cycle life and energy density of practical Li-S pouch cells. In this work, we demonstrate that a rational combination of selenium doping, core-shell hollow host structure, and fluorinated ether electrolytes enables ultrastable Li stripping/plating and essentially no polysulfide shuttle as well as fast redox kinetics. Thus, high areal capacity (>4 mAh cm -2 ) with excellent cycle stability and Coulombic efficiency were both demonstrated in Li metal anode and thick S cathode (4.5 mg cm -2 ) with a low electrolyte/sulfur ratio (10 mu L mg(-1)). Overall, this research further demonstrates a durable Li-Se/S pouch cell with high specific capacity, validating the potential practical applications.

25 ENERGY STORAGE↗
DOE OSTI2022

Current challenges in hydrate‐based desalination: Kinetic and thermodynamic perspective

Abstract Water scarcity is becoming a severe problem worldwide due to inadequate freshwater resources and swift population growth. Seawater desalination is one of the vital approaches to meet the demand for freshwater. However, energy and associated costs with conventional seawater desalination techniques are incentivizing non‐conventional water desalination processes. Water desalination using gas hydrates formation is one of the emerging non‐conventional processes. In this perspective article, recent advances in hydrate‐based seawater desalination (HBSD) have been critically analyzed to outline a future path towards a clean and efficient hydrate‐based desalination process. It provides a detailed comparison of various processes developed over decades, and measured desalination efficiencies with their process details. Moreover, the current challenges, limitations, and future perspectives of hydrate‐based desalination are also discussed. The study also recapitulates the thermodynamics and kinetics aspects of the hydrate‐based desalination process. In addition, various factors controlling the desalination efficiencies, such as control of the separation of hydrate crystals, salt deposition on hydrate particles, and hydrate morphology, were thoroughly investigated with their proposed process designs. The kinetics of hydrate formation is also assessed, with the possibility of a zero‐induction regime and its consequent impact on hydrate morphology. The current capabilities of the thermodynamics models (Gibbs energy minimization + electrolyte equation of state) were discussed using various commercially available software. Additionally, the role of hydrate promotors is also discussed, which can reduce the higher cost associated with the hydrate‐based desalination process.

Khan, Muhammad Naveed↗
DOE OSTI2023

Automated reaction kinetics and network exploration (Arkane): A statistical mechanics, thermodynamics, transition state theory, and master equation software

The open-source statistical mechanics software described here, Arkane–Automated Reaction Kinetics and Network Exploration–facilitates computations of thermodynamic properties of chemical species, high-pressure limit reaction rate coefficients, and pressure-dependent rate coefficient over multi-well molecular potential energy surfaces (PES) including the effects of collisional energy transfer on phenomenological kinetics. Arkane can use estimates to fill in information for molecules or reactions where quantum chemistry information is missing. The software solves the internal energy master equation for complex unimolecular reaction systems. Inputs to the software include converged electronic structure computations performed by the user using a variety of supported software packages (Gaussian, Molpro, Orca, TeraChem, Q-Chem, Psi4). The software outputs high-pressure limit rate coefficients and pressure-dependent phenomenological rate coefficients, as well as computed thermodynamic properties (enthalpy, entropy, and constant pressure heat capacity) with added energy corrections. Some of the key features of Arkane include treatment of 1D, 2D or ND hindered internal rotation modes, treatment of free internal rotation modes, quantum tunneling effect consideration, transition state theory (TST) and Rice-Ramsperger-Kassel-Marcus (RRKM) rate coefficient computations, master equation solution with four implemented methods, inverse-Laplace transform of high-pressure limit rate coefficients into the energy domain, energy corrections based on bond-additivity or isodesmic reactions, automated and efficient PES exploration, and PES sensitivity analysis. The present work describes the design of Arkane, how it should be used, and refers to the theory that it employs. Arkane is distributed via the RMG-Py software suite (https://github.com/ReactionMechanismGenerator/RMG-Py).

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2026

Modeling the Effects of Trimethylsilanol on Syngas Combustion Kinetics

A perturbation analysis modeling approach based on a genetic algorithm was used to identify possible reaction pathways to explain previous experimental observations of the strong acceleration of syngas auto-ignition by trimethylsilanol (TMSO). Organosilicon reactions were taken from an existing chemical kinetic mechanism for tetramethylsilane pyrolysis which also contained TMSO reactions. The experimental targets for optimization were ignition delay times and peak OH radical concentrations in the range 1010–1070 K, 5 atm with dilute (4%) ϕ = 0.1 syngas mixtures in N 2 /Ar containing 0, 200, and 1000 ppm TMSO. Hundreds of thousands of trials resulted in three models which accurately predicted the experimental auto-ignition times and peak OH concentrations. Rate of production analyses indicated that TMSO forms dimethylsilanediol, which then reacts creating two “catalytic loops.” The net effect of the loops is to accelerate the reaction H 2 + O = OH + H at a faster effective rate than H 2 /O 2 kinetics alone, thus enhancing the reactivity of syngas. The formation of the loops may be attributable to the high Si–C bond energies in siloxanols, reducing rates of thermal decomposition and allowing dimethylsilanediol to react with H 2 for a longer duration compared with its alkane analog. Here, the results of the current work provide valuable direction for fundamental studies of these new hypothesized reaction pathways.

Mansfield, Andrew B. [Eastern Michigan University,↗
DOE OSTI2025

Kinetic Investigation by Batch Processing of Film Growth during the Electrodeposition of Titanium from Ethaline

Titanium electrodeposition as a technological advance has been out of reach due to the poor film quality obtained when using previously developed methods. This study shows that the electrodeposition of Ti is possible and feasible from the deep eutectic solvent ethaline. Moreover, this study shows through batch analysis that this deposition has temperature-dependent aspects that alter the film deposition kinetics upon modest heating. This ultraviolet–visible spectroscopic study is highlighting the more facile reduction of Ti 4+ to Ti 3+ and then to Ti 2+ at elevated temperatures. Understanding the underlying kinetics of electrodeposition opens up new venues for the application of this important metal.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Thermal Stability of a Eutectic Mixture of Bis(2,2-dinitropropyl) Acetal and Formal: Part C. Kinetic Compensation Effect

Here, the aging behavior of a eutectic mixture of bis(2,2-dinitropropyl) acetal and formal [called NP here] has been studied in various atmospheres [dry (air or nitrogen) versus wet] at temperatures 70 °C and below. The properties of aged samples were analyzed using Fourier transform infrared (FTIR) spectroscopy, Karl Fischer (KF) titration, liquid chromatography/mass spectrometry (LC/MS), and thermogravimetric analysis (TGA) over a period of three years. The results indicate that at aging temperatures up to 55 °C, the initial rates of water production from nitrous acid (HONO) formation and decomposition into the water, NO, and NO 2 follows a 1st order rate law and the rate constants follow an Arrhenius law as a function of temperature. The activation energies and pre-factors for water and volatiles production yield a single linear kinetic compensation plot, suggesting a common degradation pathway between NP and the various combinations of its constituents. Within a narrow temperature range, around 55 °C, a trace amount of water in NP stabilizes its properties by preventing HONO elimination. When the aging temperature is substantially higher than 55 °C, the nature of the degradation mechanism changes. It is suspected that the degradation products of NO x , water, and HNO 3 serve as catalysts to auto-catalyze (kinetics beyond the 1st order) and further degrade NP. The effect of headspace volume on this auto-catalytic process will be discussed.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗