Rozprawy doktorskie: „Transport Process and Kinetics”

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Visuri, V. V. (Ville-Valtteri). "Mathematical modelling of chemical kinetics and rate phenomena in the AOD Process". Doctoral thesis, Oulun yliopisto, 2017. http://urn.fi/urn:isbn:9789526216713.

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Abstract Argon-oxygen decarburisation (AOD) is the most common unit process for refining stainless steel. The AOD process consists of multiple stages, in which the rate of processing is determined by complex reaction mechanisms. The main objective of this work was to study the chemical rate phenomena in selected process stages. For this purpose, an extensive literature review was conducted to clarify the main assumptions of the existing reaction models. Based on the literature review, a new categorisation of the models was proposed. In addition, a literature review was conducted to identify the main phenomena that affect the reaction kinetics in the AOD process. In this work, based on the law of mass action, a novel kinetic approach and its application for modelling of parallel mass transfer controlled reactions were studied. The developed approach enables the simultaneous solution of the chemical equilibrium and mass transfer rate which controls it. A simplified reaction model was employed for studying the effect of mass transfer rates and residual affinity on the constrained equilibrium at the reaction interface. An earlier-proposed AOD model was extended with two phenomenon-based sub-models. The top-blowing model is based on the assumption that reactions take place simultaneously at the surface of the cavity formed by the momentum of the gas jet and on the surface of the metal droplets caused by the shear force of the gas jet. The reduction model describes the reactions during the reduction stage of the AOD process by assuming that all reactions take place between the metal bath and emulsified slag droplets. The results obtained with the models were in good agreement with the measurement data collected from a steel plant. Owing to their phenomenon-based structure, the developed models are well-suited for the analysis of both existing and new production practices
Tiivistelmä Argon-happimellotus (AOD) on yleisin ruostumattoman teräksen valmistamiseen käytettävä yksikköprosessi. AOD-prosessi koostuu useista vaiheista, joissa prosessointinopeutta määrittävät monimutkaiset reaktiomekanismit. Tutkimuksen päätavoitteena oli tutkia kemiallisia nopeusilmiöitä valituissa prosessivaiheissa. Tähän liittyen tehtiin kattava kirjallisuuskatsaus, jonka tavoitteena oli tunnistaa olemassa olevien reaktiomallien pääoletukset. Kirjallisuuskatsauksen pohjalta esitettiin uusi mallien kategorisointi. Lisäksi tehtiin kirjallisuuskatsaus, jonka tavoitteena oli tunnistaa tärkeimmät reaktiokinetiikkaan vaikuttavat ilmiöt AOD-prosessissa. Tässä työssä tutkittiin uudenlaista massavaikutuksen lakiin perustuvaa lähestymistapaa sekä sen soveltamista rinnakkaisten aineensiirron rajoittamien reaktioiden mallinnukseen. Kehitetty lähestymistapa mahdollistaa kemiallisen tasapainotilan sekä sitä rajoittavan aineensiirron samanaikaisen ratkaisun. Aineensiirtonopeuksien ja jäännösaffiniteetin vaikutusta reaktiopinnalla vallitsevaan rajoitettuun tasapainotilaan tutkittiin käyttämällä yksinkertaistettua reaktiomallia. Aiemmin kehitettyä AOD-mallia laajennettiin kahdella ilmiöpohjaisella alimallilla. Lanssipuhallusmalli perustuu oletukseen, että reaktiot tapahtuvat samanaikaisesti kaasusuihkun liikemäärän muodostaman tunkeuman ja kaasusuihkun leikkausvoiman aiheuttamien metallipisaroiden pinnalla. Pelkistysmalli kuvaa AOD-prosessin pelkistysvaiheen aikana tapahtuvia reaktioita olettaen, että kaikki reaktiot tapahtuvat terässulan ja emulgoituneiden kuonapisaroiden välillä. Malleilla saadut tulokset vastasivat hyvin terästehtaalta kerättyä mittausaineistoa. Ilmiöpohjaisen rakenteensa ansiosta kehitetyt mallit soveltuvat hyvin sekä olemassa olevien että uusien tuotantopraktiikoiden analysoimiseen

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Lim, Chin Wai. "Numerical Modelling of Transient and Droplet Transport for Pulsed Pressure - Chemical Vapour Deposition (PP-CVD) Process". Thesis, University of Canterbury. Mechanical Engineering, 2012. http://hdl.handle.net/10092/6829.

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The objective of this thesis is to develop an easy-to-use and computationally economical numerical tool to investigate the flow field in the Pulsed Pressure Chemical Vapour Deposition (PP-CVD) reactor. The PP-CVD process is a novel thin film deposition technique with some advantages over traditional CVD methods. The numerical modelling of the PP-CVD flow field is carried out using the Quiet Direct Simulation (QDS) method, which is a flux-based kinetic-theory approach. Two approaches are considered for the flux reconstruction, which are the true directional manner and the directional splitting method. Both the true directional and the directional decoupled QDS codes are validated against various numerical methods which include EFM, direct simulation, Riemann solver and the Godunov method. Both two dimensional and axisymmetric test problems are considered. Simulations are conducted to investigate the PP-CVD reactor flow field at 1 Pa and 1 kPa reactor base pressures. A droplet flash evaporation model is presented to model the evaporation and transport of the liquid droplets injected. The solution of the droplet flash evaporation model is used as the inlet conditions for the QDS gas phase solver. The droplet model is found to be able to provide pressure rise in the reactor at the predicted rate. A series of parametric studies are conducted for the PP-CVD process. The numerical study confirms the hypothesis that the flow field uniformity is insensitive to the reactor geometry. However, a sufficient distance from the injection inlet is required to allow the injected precursor solution to diffuse uniformly before reaching the substrate. It is also recommended that placement of the substrate at the reactor’s centre axis should be avoided.

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Xu, Shulan. "Effect of Uncertainty of Rock Properties on Radionuclide Transport by Groundwater : Implications for Performance Assessments of the Repository of Spent Nuclear Fuel in Heterogeneous Bedrock". Doctoral thesis, Uppsala University, Department of Earth Sciences, 2000. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-544.

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The overall objective of the current study is to develop a quantitative understanding of the effects of spatial variability in physical and geochemical properties of crystalline rock on the migration of radionuclides along a single fracture in bedrock. A stochastic model was developed to describe the transport of solutes in fractured rock. The model describes the migration of radionuclides along a one-dimensional path and includes the transversal diffusion into the rock matrix and sorption kinetics. By using a Lagrangian method of description we can extend the model to the description of a two-dimensional transport problem in single fractures.

This study presents the first analysis of the impact of heterogeneous mass transfer on the transport of radionuclides in rock fractures, where most of the relevant rock properties such as aperture, porosity, effective diffusivity, sorption capacity and maximum diffusion depth are defined as being spatially random. The stochastic analysis performed here reflects the uncertainty in our knowledge of the properties associated with a discrete sampling technique in site investigations.

Geostatistics of the main parameters was determined experimentally on a large number of rock samples taken from the Swedish crystalline basement. The knowledge of the covariance functions of the main rock properties is then used as a basis for a stochastic analysis. By combining the small perturbation approach with the spectral method the problem could be solved in terms of closed form solutions for the central temporal moments of the residence time probability density function.

In order to be able to distinguish between the effects of various mechanisms from the effects of heterogeneity on the migration of radionuclides, it was necessary to perform independent studies of the effect of the variation of the dispersion coefficient on the aspect ratio of a rectangular flow section and the effect of adsorption kinetics on the migration.

Finally, the effect of the heterogeneous rock properties on the solute transport observed in a limited number of migration experiments corresponds fairly well to the theoretical effect expected on the basis of the experimentally determined auto-covariance functions.

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4

Miomandre, Fabien. "Étude de processus électrochimiques non réversibles par une méthode à base d'opérateurs". Université Joseph Fourier (Grenoble ; 1971-2015), 1995. http://www.theses.fr/1995GRE10163.

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Ce travail presente une approche nouvelle des processus electrochimiques non reversibles, reposant sur l'utilisation d'operateurs. Cette approche permet notamment de separer les contributions thermodynamique et cinetique dans la reponse du systeme a une sollicitation donnee, d'ou son interet dans l'analyse des phenomenes d'hysteresis. L'objectif est en fait de proposer une demarche alternative qui dispense de recourir a des modeles connus (fick, nernst, butler-volmer,), souvent inadequats pour l'etude de systemes electrochimiques complexes. Le principe de la methodologie consiste a representer chacune des etapes de la reaction electrochimique (transfert de charge, transferts de matiere) par un operateur. Celui-ci pouvant etre determine directement a partir des donnees experimentales, il n'est plus necessaire de postuler un modele theorique pour decrire le mecanisme de la reaction etudiee. De plus, le traitement propose est valable pour tout type de transfert obeissant a des equations lineaires. La validation experimentale de cette approche a ete realisee dans des conditions de complexite croissante: tout d'abord, dans le cas d'un couple redox a transfert de charge reversible (n-methyl phenothiazine), on a montre que l'on pouvait caracteriser le transfert de matiere et s'en servir pour prevoir la reponse du systeme a une perturbation quelconque. Puis, pour un couple redox a transfert de charge non reversible (ferro-ferricyanure), on a pu quantifier l'influence de la cinetique dans la reponse du systeme, en definissant des composantes a l'equilibre et hors equilibre experimentalement mesurables. Enfin, lorsque se superposent les effets d'un transfert de charge non reversible et de transferts de matiere mal definis (cas du polypyrrole), l'application de la methodologie a conduit a des informations originales concernant le comportement electrochimique d'un film de polymere conducteur depose sur une electrode

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5

Ince, Ceren. "Water transport kinetics in mortar-masonry systems". Thesis, University of Manchester, 2009. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.509745.

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Venugopal, Vinithra. "Kinetics of Ion Transport in Conducting Polymers". The Ohio State University, 2016. http://rave.ohiolink.edu/etdc/view?acc_num=osu1458229667.

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Leyva-Ramos, Roberto, Nahum A. Medellín-Castillo, Jovita Mendoza-Barron, Laura Fuentes-Rubio, Rosa M. Guerrero-Coronado i Raul Ocampo-Perez. "Kinetics of fluoride adsorption onto bone char". Universitätsbibliothek Leipzig, 2015. http://nbn-resolving.de/urn:nbn:de:bsz:15-qucosa-191067.

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Musabyimana, Martin. "Deammonification Process Kinetics and Inhibition Evaluation". Diss., Virginia Tech, 2008. http://hdl.handle.net/10919/29364.

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A number of innovative nitrogen removal technologies have been developed to address the treatment challenges caused by stringent regulations and increasing chemical and energy cost. A major contributing factor to these challenges is the liquid stream originating from the process of dewatering anaerobically digested solids. This liquid, also knows as centrate, reject water or sludge liquor, can cause an increase of up to 25% in ammonia loading. The recently discovered anaerobic ammonia oxidation (anammox) process is a major breakthrough for treatment of these streams as it has the potential to remove up to 85% of nitrogen load without external carbon source addition. The anammox process is combined with another process that oxidizes half of the ammonia to nitrite (nitritation) in a separate reactor such as in the SHARON process, or in the same reactor such as in the DEaMmONification (DEMON) process. Despite intensive laboratory research for the last 10 years to fully understand these processes, there is still a high level of skepticism surrounding the implementation of full-scale systems. The reason for this skepticism could be due to frequent failures observed in the lab scale systems as well as reported slow bacterial growth. We think that this technology might be used more effectively in the future if process kinetics, inhibition and toxicity can be better understood. This work focused on the DEMON process with a goal to understand the kinetics and inhibition of the system as a whole and the anammox process in particular. A DEMON pilot study was undertaken at the Alexandria Sanitation Authority (ASA) and had several study participants, including ASA, the District of Columbia Water and Sewer Authority (DCWASA), CH2M Hill Inc., Envirosim Ltd, the University of Innsbruck and Virginia Tech. We investigated the growth rate of anammox bacteria within a quasi-optimal environment. Laboratory-scale experiments were conducted to assess anaerobic ammonia oxidation inhibition by nitrite as well as aerobic ammonia oxidation inhibition by compounds present in the DEMON reactor feed, such as a defoaming agent, a sludge conditioning polymer, and residual iron from phosphorus removal practices. The study revealed that the DEMON process can be efficiently controlled to limit nitrite accumulation capable of causing process inhibition. The target ammonium loading rate of 0.5 kg/m3/d was reached, and no upset was noticed for a loading up to 0.80 kg/m3/d with an HRT of 1.7 days. The ammonia removal efficiency reached an average of 76% while total nitrogen removal efficiency had an average of 52%. Most of the process upsets were caused by aerobic ammonia oxidation failure rather than anammox inhibition. Failure in ammonia oxidation affected pH control, a variable which is at the center of the DEMON process control logic. The pilot study is summarized in Chapter 3 of this Dissertation. The low anammox maximum specific growth rate (Âµmax,An) as well as nitrite inhibition are historically reported to be the major process challenges according to the literature, but the degree to which each contributes to process problems differs widely in the literature. In this study, we estimated Âµmax,An by using the high F:M protocol commonly used for nitrifying populations. We also studied the effect of both short term and sustained nitrite exposure on anammox activity. In this study, Âµmax,An was estimated to be 0.017 h-1. The study results also suggest that anammox bacteria can tolerate a spike of nitrite-N at concentrations as high as 400 mg/L as long as this concentration is not sustained. Sustained concentrations above 50 mg/L caused a gradual loss of activity over the long term. Finally, the inhibition of aerobic ammonia oxidizing bacteria (AerAOB) observed in the DEMON reactor was investigated using laboratory experiments and is reported in Chapter 6. AerAOB inhibition was, in most cases, the main reason for process upset. Compounds that were suspected to be the cause of the inhibition were tested. The study noticed that a defoaming agent, polymer and ferrous iron had some inhibiting properties at the concentrations tested.
Ph. D.

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Katoch, Sunain, Vinay Sharma i Patit Paban Kundu. "Swelling kinetics of unsaturated polyester–layered silicate nanocomposite". Universitätsbibliothek Leipzig, 2015. http://nbn-resolving.de/urn:nbn:de:bsz:15-qucosa-186443.

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Kinetics of swelling and sorption behavior of unsaturated polyester nanocomposite (based on glycolyzed PET, maleic anhydride, styrene, and montmorillonite) synthesized by two different mixing methods, simultaneous and sequential is studied in acetic acid at different temperatures. The values of n in the transport equation are found to be below 0.5, showing non-Fickian or pseudo-Fickian transport in the polymers. The dependence of diffusion coefficient on the mixing methods and temperature has also been studied for the unsaturated polyester nanocomposite. The diffusion coefficients in simultaneous mixing samples decrease with an increase in the mixing time in the samples. In case of the sequential mixing samples, the diffusion coefficient increases with an increase in mixing time. The diffusion coefficient increases with an increase in temperature for all the unsaturated polyester nanocomposite samples. The sorption coefficient increases with an increase in the mixing time for all the samples synthesized by in-situ mixing method. The crosslink density (calculated from the CH3COOH swelling) ranges from 5.014 to 7.092 × 102 mol/cm3 for simultaneous mixed samples and 5.212 to 7.192 × 102 mol/cm3 for sequentially mixed samples.

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Leyva-Ramos, Roberto, Raul Ocampo-Perez, Oliva L. Torres-Rivera, Maria S. Berber-Mendoza i Nahum A. Medellin-Castillo. "Kinetics of pyridine adsorption onto granular activated carbon". Universitätsbibliothek Leipzig, 2015. http://nbn-resolving.de/urn:nbn:de:bsz:15-qucosa-191056.

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Song, Young Chul. "Kinetics of water transport in ultraviscous organic aerosol". Thesis, University of Bristol, 2017. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.752782.

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Jaburek, Martin. "Kinetics and regulation of mitochondrial cation transport systems /". Full text open access at:, 1999. http://content.ohsu.edu/u?/etd,207.

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Haas, Ole-Erich, Jean-Marc Simon i Signe Kjelstrup. "Adsorption-desorption kinetics of H 2 molecules on graphite". Universitätsbibliothek Leipzig, 2015. http://nbn-resolving.de/urn:nbn:de:bsz:15-qucosa-189614.

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Radchenko, Taras, Valentyn Tatarenko i Hélèna Zapolsky. "Diffusional atomic-ordering kinetics of close-packed solid solutions". Universitätsbibliothek Leipzig, 2016. http://nbn-resolving.de/urn:nbn:de:bsz:15-qucosa-193505.

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Davies, Matthew Lloyd. "Exploiting nonlinear kinetics to enhance process operability". Thesis, University of Leeds, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.270897.

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Legalatladi, Seetsela. "The kinetics of endosome processing". Master's thesis, University of Cape Town, 1995. http://hdl.handle.net/11427/27047.

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The present thesis looks at the behaviour of internalised cell surface-derived membrane marker in comparison with the behaviour of endocytosed HRP (horse-radish peroxidase) as a fluid-phase contents marker. The pooling and/or segregation in the endosome was measured by determining co-localization with HRP. Colocalization of the two markers in the endosome is studied by using the ability of HRP to catalyse the crosslinking of membrane marker in endosomes with DAB (3,3'-diaminobenzidine), rendering the membrane marker detergent insoluble. To study the kinetic behaviour of membrane marker, radioactive galactose was covalently bound to cell-surface glycoconjugates on mouse macrophage-cells, P388D₁, as catalysed by galactosyltransferase. This provided a general membrane marker. After endocytosis-derived redistribution of membrane marker between the cell surface and endosomal membrane, a steady state was established with about 16% of the label on internal membranes. The bulk of the label on the cell surface was removable by subsequent treatment with β-galactosidase.

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Leyva-Ramos, Roberto, Nahum A. Medellín-Castillo, Jovita Mendoza-Barron, Laura Fuentes-Rubio, Rosa M. Guerrero-Coronado i Raul Ocampo-Perez. "Kinetics of fluoride adsorption onto bone char". Diffusion fundamentals 11 (2009) 84, S. 1-2, 2009. https://ul.qucosa.de/id/qucosa%3A14056.

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Amikiya, Emmanuel Adoliwine. "Numerical simulation of chemical kinetics transport and flow processes". Thesis, University of Pretoria, 2020. http://hdl.handle.net/2263/77830.

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In this thesis, numerical solution procedures are developed for simulating chemical phenomena. Mathematical models for phenomena involving flow, transport and reaction of chemical species are computationally challenging to simulate due to stiffness, high degrees of freedom and spatial dependence. Such challenges are resolved (in this thesis) by combining model decoupling techniques with compatible efficient numerical schemes. Chemical phenomena is decomposed into well-mixed chemical systems, poorly-mixed systems (or spatial dependent kinetics) and flow with reactive transport systems. Mathematical models for the systems are Ordinary Differential Equations (ODEs), parabolic Partial Differential Equations (PDEs) and hyperbolic PDEs, respectively. In the ODE model, stiffness is resolved by positivity-preserving implicit schemes while the large degrees of freedom is reduced by stoichiometric and continuous-time iteration methods. In the parabolic model, model decoupling techniques are employed to reduce the degrees of freedom while Implicit-Explicit numerical schemes are presented for resolving stiffness. Further, numerical schemes that have dispersion-dissipation-preserving properties have also been discussed. In the hyperbolic model, model decoupling techniques have been presented for reducing the degrees of freedom while shock-capturing, well-balanced numerical schemes have been presented for resolving nonlinear hyperbolic effects. The results from experiments show that the proposed numerical solution procedures can efficiently resolve the challenges in simulating chemical phenomena.
Thesis (PhD)--University of Pretoria, 2020.
Mathematics and Applied Mathematics
PhD
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Leyva-Ramos, Roberto, Raul Ocampo-Perez, Oliva L. Torres-Rivera, Maria S. Berber-Mendoza i Nahum A. Medellin-Castillo. "Kinetics of pyridine adsorption onto granular activated carbon". Diffusion fundamentals 11 (2009) 83, S. 1-2, 2009. https://ul.qucosa.de/id/qucosa%3A14054.

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20

Larisch, Wolfgang. "4 Coupled compartments – an analytical solution for diffusion and reaction kinetics". Universitätsbibliothek Leipzig, 2016. http://nbn-resolving.de/urn:nbn:de:bsz:15-qucosa-198373.

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Adhoum, Nafaâ. "Insertion du sodium et pénétration de l’électrolyte dans le carbone en milieu NaF fondu à 1025°C". Grenoble INPG, 1996. http://www.theses.fr/1996INPG0185.

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Pendant l’électro-élaboration de l’aluminium par le procédé Hall-Héroult en milieu de cryolite fondue, il y a production parasite de sodium qui imprègne le carbone du bloc cathodique, suivi de près par l’électrolyte. Ceci provoque le gonflement du carbone et conduit à la limitation de la durée de vie de la cellule d’électrolyse. Dans l’objectif d’élucider les mécanismes d’interaction entre le sodium et le carbone, nous avons mené une étude de cinétique électrochimique en milieu NaF pur fondu à 1025°C. L’utilisation de diverses techniques électrochimiques (voltampérométrie, chronopotentiométrie et coulométrie) a mis en évidence l’existence d’une interaction complexe entre le sodium et le carbone. En effet, le métal alcalin est distribué entre deux types de sites correspondant à deux activités différentes. La forme la moins fortement liée au carbone correspond au sodium piégé dans la micro-porosité, alors que la forme plus stable est attribuée au sodium inséré entre les plans de graphène. Nous avons aussi montré l’existence d’un transfert lent et irréversible des espèces piégées vers les sites normaux d’insertion. De plus, en raison de l’évaporation du sodium à partir de l’interface, le produit Na-C subit une décomposition. Le transport du métal alcalin dans le réseau hôte est limité par une transition de phase du premier ordre. En tenant compte de toutes ces observations expérimentales, nous avons proposé un mécanisme réactionnel, construit le modèle mathématique associé et résolu le système d’équations différentielles, ainsi obtenu, en utilisant la méthode des différences finies. Les résultats obtenus montrent un bon accord entre les courbes théoriques et les résultats expérimentaux et permettent l’estimation des différents paramètres cinétiques des processus d’interaction Na-C. Enfin, nous avons montré que la pénétration du sodium provoque un changement de la tension interfaciale NaF-C et induit la progression du bain fondu par capillarité à partir d’une fraction molaire minimale en sodium (XNa=1,4. 10-2)
One of the most important factors causing the failure of carbon cathode, during aluminum electrolysis by Hall-Héroult process, is the uptake of sodium which leads to a macroscopic swelling of cathode. To understand the fundamental mechanism of sodium-carbon interaction, we carried our electrochemical kinetic study in a pure molten NaF electrolyte at 1025°C. We proved the occurrence of a complex interaction between sodium and carbon. Indeed, sodium is showed to be distributed between two kinds of sites in the host material : normal sites in the Van der Wals gap between the carbon’s plans and traps which are located at microporosity and dislocations. We also showed the occurrence of a slow and irreversible transfer of sodium from traps to normal intercalation sites. Moreover, sodium transport in carbon matrix is found to be limited by a first order phase transition. Taking into account all these experimental observations, we suggested a complete mechanism scheme and developed a mathematical model which allowed the recovery, with a good accuracy of the experimental results

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Walmsley, A. R. "The kinetics of glucose transport in human red blood cells". Thesis, University of Manchester, 1986. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.377727.

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Hsu, Jaanpyng. "Swelling, mass transport, and chemical kinetics in bituminous coal pyrolysis". Thesis, Massachusetts Institute of Technology, 1989. http://hdl.handle.net/1721.1/39029.

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Shi, Jianmin, i Klaus-Dieter Becker. "Kinetics of cation site-exchange in complex oxides by optical relaxation spectroscopy". Universitätsbibliothek Leipzig, 2015. http://nbn-resolving.de/urn:nbn:de:bsz:15-qucosa-186700.

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Kaganovskii, Yuri, Andrey A. Lipovskii, Emma Mogilko, Valentina Zhurikhina i Michael Rosenbluh. "Kinetics of bulk nano-clustering in silver-doped glasses during reactive hydrogen diffusion". Universitätsbibliothek Leipzig, 2016. http://nbn-resolving.de/urn:nbn:de:bsz:15-qucosa-193695.

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Cochain, Benjamin, V. Magnien, Daniel R. Neuville i Pascal Richet. "Diffusion in silicate melts: kinetics and mechanisms of redox reactions". Diffusion fundamentals 6 (2007) 77, S. 1, 2007. https://ul.qucosa.de/id/qucosa%3A14257.

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Frömberg, Daniela. "Reaction Kinetics under Anomalous Diffusion". Doctoral thesis, Humboldt-Universität zu Berlin, Mathematisch-Naturwissenschaftliche Fakultät I, 2011. http://dx.doi.org/10.18452/16374.

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Die vorliegende Arbeit befasst sich mit der Verallgemeinerung von Reaktions-Diffusions-Systemen auf Subdiffusion. Die subdiffusive Dynamik auf mesoskopischer Skala wurde mittels Continuous-Time Random Walks mit breiten Wartezeitverteilungen modelliert. Die Reaktion findet auf mikroskopischer Skala, d.h. während der Wartezeiten, statt und unterliegt dem Massenwirkungsgesetz. Die resultierenden Integro-Differentialgleichungen weisen im Integralkern des Transportterms eine Abhängigkeit von der Reaktion auf. Im Falle der Degradation A->0 wurde ein allgemeiner Ausdruck für die Lösungen beliebiger Dirichlet-Randwertprobleme hergeleitet. Die Annahme, dass die Reaktion dem Massenwirkungsgesetz unterliegt, ist eine entscheidende Voraussetzung für die Existenz stationärer Profile unter Subdiffusion. Eine nichtlineare Reaktion stellt die irreversible autokatalytische Reaktion A+B->2A unter Subdiffusion dar. Es wurde ein Analogon zur Fisher-Kolmogorov-Petrovskii-Piscounov-Gleichung (FKPP) aufgestellt und die resultierenden propagierenden Fronten untersucht. Numerische Simulationen legten die Existenz zweier Regimes nahe, die sowohl mittels eines Crossover-Argumentes als auch durch analytische Berechnungen untersucht wurden. Das erste Regime ist charakterisiert durch eine Front, deren Breite und Geschwindigkeit sich mit der Zeit verringert. Das zweite, fluktuationsdominierte Regime liegt nicht im Geltungsbereich der kontinuierlichen Gleichung und weist eine stärkere Abnahme der Frontgeschwindigkeit sowie eine atomar scharf definierte Front auf. Ein anderes Szenario, bei dem eine Spezies A in ein mit immobilen B-Partikeln besetztes Medium hineindiffundiert und gemäß dem Schema A+B->(inert) reagiert, wurde ebenfalls betrachtet. Diese Anordnung wurde näherungsweise als ein Randwertproblem mit einem beweglichen Rand (Stefan-Problem) formuliert. Die analytisch gewonnenen Ergebnisse bzgl. der Position des beweglichen Randes wurden durch numerische Simulationen untermauert.
The present work studies the generalization of reaction-diffusion schemes to subdiffusion. The subdiffusive dynamics was modelled by means of continuous-time random walks on a mesoscopic scale with a heavy-tailed waiting time pdf lacking the first moment. The reaction was assumed to take place on a microscopic scale, i.e. during the waiting times, obeying the mass action law. The resultant equations are of integro-differential form, and the reaction explicitly affects the transport term. The long ranged memory of the subdiffusion kernel is modified by a factor accounting for the reaction of particles during the waiting times. The degradation A->0 was considered and a general expression for the solution to arbitrary Dirichlet Boundary Value Problems was derived. For stationary solutions to exist in reaction-subdiffusion, the assumption of reactions according to classical rate kinetics is essential. As an example for a nonlinear reaction-subdiffusion system, the irreversible autocatalytic reaction A+B->2A under subdiffusion is considered. A subdiffusive analogue of the classical Fisher-Kolmogorov-Petrovskii-Piscounov (FKPP) equation was derived and the resultant propagating fronts were studied. Two different regimes were detected in numerical simulations, and were discussed using both crossover arguments and analytic calculations. The first regime is characterized by a decaying front velocity and width. The fluctuation dominated regime is not within the scope of the continuous description. The velocity of the front decays faster in time than in the continuous regime, and the front is atomically sharp. Another setup where reactants A penetrate a medium initially filled with immobile reactants B and react according to the scheme A+B->(inert) was also considered. This problem was approximately described in terms of a moving boundary problem (Stefan-problem). The theoretical predictions concerning the moving boundary were corroborated by numerical simulations.

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28

Li, Huayu. "Process measurements and kinetics of unseeded batch cooling crystallization". Diss., Georgia Institute of Technology, 2015. http://hdl.handle.net/1853/53503.

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This thesis describes the development of an empirical model of focus beam reflectance measurements (FBRM) and the application of the model to monitoring batch cooling crystallization and extracting information on crystallization kinetics. Batch crystallization is widely used in the fine chemical and pharmaceutical industries to purify and separate solid products. The crystal size distribution (CSD) of the final product greatly influences the product characteristics, such as purity, stability, and bioavailability. It also has a great effect on downstream processing. To achieve a desired CSD of the final product, batch crystallization processes need to be monitored, understood, and controlled. FBRM is a promising technique for in situ determination of the CSD. It is based on scattering of laser light and provides a chord-length distribution (CLD), which is a complex function of crystal geometry. In this thesis, an empirical correlation between CSDs and CLDs is established and applied in place of existing first-principles FBRM models. Built from experimental data, the empirical mapping of CSD and CLD is advantageous in representing some effects that are difficult to quantify by mathematical and physical expressions. The developed model enables computation of the CSD from measured CLDs, which can be followed during the evolution of the crystal population during batch cooling crystallization processes. Paracetamol, a common drug product also known as acetaminophen, is selected as the model compound in this thesis study. The empirical model was first established and verified in a paracetamol-nonsolvent (toluene) slurry, and later applied to the paracetamol-ethanol crystallization system. Complementary to the FBRM measurements, solute concentrations in the liquid phase were determined by in situ infrared spectra, and they were jointly implemented to monitor the crystallization process. The framework of measuring the CSD and the solute concentration allows the estimation of crystallization kinetics, including those for primary nucleation, secondary nucleation, and crystal growth. These parameters were determined simultaneously by fitting the full population balance model to process measurements obtained from multiple unseeded paracetamol-ethanol crystallization runs. The major contributions of this thesis study are (1) providing a novel methodology for using FBRM measurements to estimate CSD; (2) development of an experimental protocol that provided data sets rich in information on crystal growth and primary and secondary nucleation; (3) interpretation of kinetics so that appropriate model parameters could be extracted from fitting population balances to experimental data; (4) identification of the potential importance of secondary nucleation relative to primary nucleation. The protocol and methods developed in this study can be applied to other systems for evaluating and improving batch crystallization processes.

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29

Kaganovskii, Yuri, Andrey A. Lipovskii, Emma Mogilko, Valentina Zhurikhina i Michael Rosenbluh. "Kinetics of bulk nano-clustering in silver-doped glasses during reactive hydrogen diffusion: Kinetics of bulk nano-clustering in silver-doped glasses duringreactive hydrogen diffusion". Diffusion fundamentals 6 (2007) 42, S. 1-2, 2007. https://ul.qucosa.de/id/qucosa%3A13168.

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30

Davie, R. J. "The uptake and transport of zinc in isolated intestinal mucosa". Thesis, Open University, 1988. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.234707.

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31

Katoch, Sunain, Vinay Sharma i Patit Paban Kundu. "Swelling kinetics of unsaturated polyester and their montmorillonite filled nanocomposite synthesized from glycolyzed PET". Universitätsbibliothek Leipzig, 2015. http://nbn-resolving.de/urn:nbn:de:bsz:15-qucosa-186158.

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The solvent resistance properties of the unsaturated polyster and their montmorillonite filled nanocomposites are studied in acetic through equilibrium swelling method at different temperatures. The kinetics of sorption is studied by using the equation of transport phenomena. The values of ‘n’ in solvent transport equation are found to be below ‘0.5’, showing the non-Fickian or pseudo-Fickian transport in the polymer. The dependence of diffusion coefficient on composition and temperature has been studied for all polymeric samples. The diffusion coefficient of unsaturated polyester samples decreases with an increase in unsaturated acid content. The nanocomposite samples show low diffusion coefficient than corresponding pristine polymers. The diffusion coefficient, sorption coefficient and permeation coefficient increase with an increase in temperature for all samples. The crosslink density for neat polymer with varied unsaturated acid content ranges from 2.98 to 3.52 ×105mol/cm3. For the nanocomposite samples it ranges from 3.70 to 5.72 × 105 mol/cm3.

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32

Ruthven, Douglas M. "Adsorption and desorption kinetics for diffusion controlled systems with a strongly concentration dependent diffusivity". Universitätsbibliothek Leipzig, 2016. http://nbn-resolving.de/urn:nbn:de:bsz:15-qucosa-193874.

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The formal solution to the diffusion equation for transient adsorption in a semiinfinite medium with a strongly concentration dependent diffusivity, originally derived by Fujita ( 3 ), has been extended to desorption. Profiles for adsorption and desorption are compared and simplified asymptotic expressions which are useful when the diffusivity ratio is large are derived. The effect of a strongly concentration dependent diffusivity on adsorption and desorption kinetics is briefly considered.

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33

Kuzovkov, Vladimir N., Eugene A. Kotomin, Anatoli I. Popov i Rafael Vila. "Diffusion-controlled kinetics of metallic colloid formation in irradiated Al2O3, MgO and NaCl crystals". Universitätsbibliothek Leipzig, 2016. http://nbn-resolving.de/urn:nbn:de:bsz:15-qucosa-198353.

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34

Prokofjev, Sergei I., Erik Johnson i Ulrich Dahmen. "Kinetics of dissolution of liquid Pb nano-inclusions attached to a dislocation in aluminum". Universitätsbibliothek Leipzig, 2016. http://nbn-resolving.de/urn:nbn:de:bsz:15-qucosa-198539.

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35

Chen, Jiaping. "Sorption of metal ions from aqueous solutions : equilibrium, kinetics, and transport". Diss., Georgia Institute of Technology, 1997. http://hdl.handle.net/1853/21467.

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36

Ma, Wen Ph D. Massachusetts Institute of Technology. "Initial oxidation of zirconium : chemistry, atomic structure, transport and growth kinetics". Thesis, Massachusetts Institute of Technology, 2016. http://hdl.handle.net/1721.1/117452.

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Thesis: Ph. D., Massachusetts Institute of Technology, Department of Nuclear Science and Engineering, 2016.
Cataloged from student-submitted PDF version of thesis.
Includes bibliographical references (pages 175-184).
The objective of this thesis is to uncover the chemical states and atomic structure of the initial oxide on zirconium and the oxygen transport kinetics through this oxide under electric field. This goal is important for enabling more accurate zirconium oxidation models, for example for nuclear reactor materials, as well as for assessing the mechanisms that govern the performance of zirconia based technologies, such as redox based resistive switching memory devices, gate dielectric for metal oxide semiconductor devices, and electrolytes for solid oxide fuel cells ...
by Wen Ma.
Ph. D.

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37

Larisch, Wolfgang. "4 Coupled compartments – an analytical solution for diffusion and reaction kinetics". Diffusion fundamentals 24 (2015) 32, S. 1, 2015. https://ul.qucosa.de/id/qucosa%3A13497.

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38

Ruthven, Douglas M. "Adsorption and desorption kinetics for diffusion controlled systems with a strongly concentration dependent diffusivity: Adsorption and desorption kinetics for diffusion controlledsystems with a strongly concentration dependent diffusivity". Diffusion fundamentals 6 (2007) 51, S. 1-11, 2007. https://ul.qucosa.de/id/qucosa%3A14230.

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The formal solution to the diffusion equation for transient adsorption in a semiinfinite medium with a strongly concentration dependent diffusivity, originally derived by Fujita ( 3 ), has been extended to desorption. Profiles for adsorption and desorption are compared and simplified asymptotic expressions which are useful when the diffusivity ratio is large are derived. The effect of a strongly concentration dependent diffusivity on adsorption and desorption kinetics is briefly considered.

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39

Weber, Sven-Ulf, Oliver Bartels i Klaus-Dieter Becker. "A variable-temperature Mössbauer study into the structure, disorder and formation kinetics of iron nitrides". Universitätsbibliothek Leipzig, 2015. http://nbn-resolving.de/urn:nbn:de:bsz:15-qucosa-188057.

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40

Chowdhury, Debashish. "First passage times: a common theme in the kinetics of macromolecular motors". Diffusion fundamentals 20 (2013) 12, S. 1, 2013. https://ul.qucosa.de/id/qucosa%3A13534.

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41

Shi, Jianmin, i Klaus-Dieter Becker. "Kinetics of cation site-exchange in complex oxides by optical relaxation spectroscopy". Diffusion fundamentals 12 (2010) 31, 2010. https://ul.qucosa.de/id/qucosa%3A13877.

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42

Simon, Jean-Marc, i Jean-Pierre Bellat. "Adsorption kinetics of mixtures of n-hexane and 2-methylpentane on silicalite by nonequilibrium molecular dynamics". Universitätsbibliothek Leipzig, 2016. http://nbn-resolving.de/urn:nbn:de:bsz:15-qucosa-193628.

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43

Sterling, Michael Conroy Jr. "Aggregation and transport kinetics of crude oil and sediment in estuarine waters". Texas A&M University, 2003. http://hdl.handle.net/1969.1/572.

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Modeling the transport and fate of spilled crude oil is important for estimating short and long-term toxicity effects in coastal ecosystems. This research project investigates the partitioning of hydrocarbons from a surface crude oil slick, the resurfacing of chemically dispersed crude oil droplets, the suitability of in-situ field instruments for oil and sediment characterization, and the aggregation and settling of dispersed oil and suspended sediments. An initial laboratory study was conducted to investigate apparent hydrocarbon solubility in petroleum/water systems. Mixing shear and initial crude oil layer thickness were related empirically to oil entrainment rate. A model describing hydrocarbons partitioned in colloidal and soluble phases was consistent with experimental data. A second laboratory study was conducted to investigate the influence of coalescence kinetics on mean droplet size and resurfacing rate of chemically dispersed crude oil droplets. Increased mean shear rates resulted in mean droplet diameters and oil resurfacing rates. A third laboratory study was conducted to compare particle size and fractal dimension measurements obtained using a submersible flow cytometer, an electrozone particle counter, and a light scattering particle sizer. Measured particles included latex beads, crude oil, clay, crude oil-clay aggregates, and crude oil-silica aggregates. Tested instruments gave consistent size measurements for all particle systems, suggesting their suitability for sizing marine particles. To describe the aggregation kinetics of oil-sediment systems, a modified Smoluchowski model based on coalesced sphere (CS) assumptions was developed. Observed collision efficiency values (αOBS) were related to collision efficiency values for single particle type systems (αHOMO) and those for two particle type systems (αHET) using a probabilistic approach. For clay and crude oil, αHOMO values were higher than the αHOMO value for silica. Clay-oil and silica-oil have similar αHET values. Thus, crude oil can significantly increase the aggregation rates of noncohesive sediments such as silica. The CS model above was modified to incorporate sediment fractal geometry. The ability of this modified coalesced fractal sphere (mCFS) model to fit experimental data sets was better than that of a coalesced sphere (CS) model. Because of their reduced settling rates, sediments with lower fractal dimension form more aggregate with dispersed oil.

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44

Atay, N. Z. "Transport and interfacial exchange kinetics in one- and two-phase disperse systems". Thesis, University of Kent, 1987. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.374831.

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45

Haubrock, Jens. "The process of dimethyl carbonate to diphenyl carbonate: thermodynamics, reaction kinetics and conceptual process design". Enschede : University of Twente [Host], 2007. http://doc.utwente.nl/58404.

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46

Katoch, Sunain, Vinay Sharma i Patit Paban Kundu. "Swelling kinetics of unsaturated polyester–layered silicate nanocomposite: depending on the fabrication method". Diffusion fundamentals 13 (2010) 1, S. 1-31, 2010. https://ul.qucosa.de/id/qucosa%3A13860.

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Kinetics of swelling and sorption behavior of unsaturated polyester nanocomposite (based on glycolyzed PET, maleic anhydride, styrene, and montmorillonite) synthesized by two different mixing methods, simultaneous and sequential is studied in acetic acid at different temperatures. The values of n in the transport equation are found to be below 0.5, showing non-Fickian or pseudo-Fickian transport in the polymers. The dependence of diffusion coefficient on the mixing methods and temperature has also been studied for the unsaturated polyester nanocomposite. The diffusion coefficients in simultaneous mixing samples decrease with an increase in the mixing time in the samples. In case of the sequential mixing samples, the diffusion coefficient increases with an increase in mixing time. The diffusion coefficient increases with an increase in temperature for all the unsaturated polyester nanocomposite samples. The sorption coefficient increases with an increase in the mixing time for all the samples synthesized by in-situ mixing method. The crosslink density (calculated from the CH3COOH swelling) ranges from 5.014 to 7.092 × 102 mol/cm3 for simultaneous mixed samples and 5.212 to 7.192 × 102 mol/cm3 for sequentially mixed samples.

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47

Haas, Ole-Erich, Jean-Marc Simon i Signe Kjelstrup. "Adsorption-desorption kinetics of H 2 molecules on graphite: a molecular dynamics study". Diffusion fundamentals 11 (2009) 29, S. 1-2, 2009. https://ul.qucosa.de/id/qucosa%3A13978.

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48

Simon, Jean-Marc, Edith Fardet-Lemaire, Igor Bezverkhyy, Jean-Pierre Bellat i Florence Baras. "Kinetics of adsorption of linear and branched C6 alkanes onto ZSM-5 zeolite - experiments and molecular simulations". Universitätsbibliothek Leipzig, 2016. http://nbn-resolving.de/urn:nbn:de:bsz:15-qucosa-195653.

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49

Singare, Pravin U. "Ion-Isotopic exchange reaction kinetics in characterization of anion exchange resins Dowex 550A LC and Indion-820". Universitätsbibliothek Leipzig, 2015. http://nbn-resolving.de/urn:nbn:de:bsz:15-qucosa-184151.

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The present paper involves application of nondestructive radioactive tracer technique in characterization of Dowex 550A LC and Indion-820 anion exchange resins. The characterization study was based on kinetic of exchange reactions between inactive iodide/bromide ions on the resins with radioactive iodide/bromide ions in the solution. During iodide exchange reaction performed at a constant temperature of 40.00C, using 1.000 g of ion exchange resins and labeled iodide ion solution of concentration 0.003 mol/L, for Dowex 550A LC resin the specific reaction rate and initial rate of ion exchange was 0.271 min-1 and 0.141 mmol/min respectively, while the amount of iodide ions exchanged was 0.522 mmol, and log Kd was calculated to be 12.1. The above values calculated for Dowex 550A LC resin was higher than the respective values of 0.108, 0.330, 0.036 and 6.0 as obtained for Indion-820 resins. Similar results were obtained for the two resins during bromide exchange reactions, thereby indicating superior performance of Dowex 550A LC resin over Indion-820 resins.

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50

Harris, Rosemary J., Jevgenijs Kaupužs i Reinhard Mahnke. "Metastability in the zero-range process". Universitätsbibliothek Leipzig, 2016. http://nbn-resolving.de/urn:nbn:de:bsz:15-qucosa-195303.

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