The main objective of this thesis is to study the fundamental behaviour of multi-component gas mixture flows in micro/nano-channels undergoing catalytic chemical reactions on the walls. This work is primarily focused on nano-scale reacting flows seen in related applications; especially, miniaturized energy sources such as micro-fuel cells and batteries. At these geometries, the order of the characteristic length is close to the mean free path of the flowing gas, making the flow highly rarefied. As a result, non-equilibrium conditions prevail even the bulk flow and therefore, continuum assumptions are not held anymore. Hence, discrete methods should be adopted to simulate molecular movements and interactions described by the Boltzmann equation. The Direct Simulation Monte Carlo (DSMC) method was employed for the present research due to its natural ability for simulating a broad range of rarefied gas flows, and its flexibility to incorporate surface chemical reactions. In the first step, fluid dynamics and the heat transfer of H₂/N₂ and H₂/N₂/CO₂ gas mixture slip flows in a plain micro-channel are simulated. The obtained results are compared to the corresponding data achieved from Navier-Stokes equations with slip/jump boundary conditions. Generally, very good agreements are observed between the two methods. It proves the ability of DSMC in replicating the fluid properties of multi-component gas mixtures even when high mass discrepancies exist among the species. Based on this comparison, the proper parameters are set for the prepared DSMC code, and the appropriate intermolecular collision model is identified. It is also found that stream variables should be calculated more accurately at flow boundaries in order to simulate the intense upstream diffusion emerging at low velocity flows frequently seen in micro/nano-applications. Therefore, in the second step, a novel pressure boundary condition is introduced for gas mixture flows by substituting the commonly used Maxwell velocity distribution with the Chapman-Enskog distribution function. It is shown that this new method yields better results for lower velocity and higher rarefaction level cases. In the last step, a new method is proposed for coupling the flow field simulated by DSMC and surface reactions modelled by the species conservation ODE system derived from the reaction mechanism. First, a lean H₂/air slip flow subjected to oxidation on platinum coated walls in a flat micro-channel 4μm in height is simulated as a verification test case. The results obtained are validated against the solutions of the Navier-Stokes equations with slip/jump boundary conditions and very good conformity is achieved. Next, several cases undergoing the same reaction with Reynolds numbers ranging from 0.2 to 3.6 and Knudsen numbers ranging from 0.025 to 0.375, are simulated using the verified code to investigate the effects of the channel height ranging from 0.5μm to 2μm , the inlet mass flow rate ranging from 5 kg/m².s to 25 kg/m².s, the inlet temperature ranging from 300K to 700K, the wall temperature ranging from 300K to 1000K, and the fuel/air equivalence ratio ranging from 0.28 to 1.5. Some of the findings are as follows: (1) increasing the surface temperature from 600K to 1000K and/or the inlet temperature from 300K to 700K results in negligible enhancement of the conversion rate, (2) the optimum value of the equivalence ratio is on the fuel lean side (around 0.5), (3) the efficiency of the reactor is higher for smaller channel heights, and (4) increasing the inlet mass flux elevates the reaction rate especially for the smaller channels; this effect is not linear and is more magnified for lower mass fluxes.

No description available.

Thesis (D.Sc.)--University of Adelaide, School of Chemistry and Physics, Discipline of Chemistry, 2005? / "December 2004" Includes bibliographical references.

Orientador: Maria Regina Wolf Maciel / Tese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia Química / Made available in DSpace on 2018-08-20T04:52:13Z (GMT). No. of bitstreams: 1 PlazasTovar_Laura_D.pdf: 30398679 bytes, checksum: 294839d0c5d272ef9b42f68de9ede471 (MD5) Previous issue date: 2012 / Resumo: O processo de destilação molecular reativa, no qual ocorre o acoplamento de destilação molecular e reação química simultaneamente, pode ser qualificado como um processo híbrido e também como um processo intensificado, dada a configuração do equipamento e as condições operacionais que viabilizam a implementação de alto vácuo (<50 Pa), permitindo submeter o material a temperaturas adequadas num curto tempo operacional, garantindo um contato muito intenso da amostra com a superfície catalítica. Este trabalho teve como finalidade desenvolver a modelagem matemática e simulação do processo de destilação molecular centrífuga reativa (DMCR - em catálise heterogênea) baseada na descrição matemática descrita para o processo de destilação molecular centrífuga de frações pesadas de petróleo. Para a simulação, foi considerado como caso de estudo o processamento do resíduo atmosférico "ATR-W" 673,15 K+ com grau API igual a 11,9 e massa molar igual a 2956 kg·kmol-1. A modelagem e simulação foram realizadas nas condições de estado estacionário. O conjunto de (11+18N) equações diferenciais parciais e algébricas e (27+19N) variáveis foi incorporado no ambiente computacional, denominado DESTMOL-R, desenvolvido na linguagem FORTRAN-90 usando o compilador Compaq Visual Fortran (professional edition 6.6). O sistema de equações formuladas no filme, ao longo da superfície cônica do evaporador, foi resolvido numericamente através do método das linhas. Condições de temperatura do evaporador entre 473.15K e 523.15 K e de porcentagem de catalisador (catalisador zeolítico regenerado de uma unidade de FCC) entre 3 e 5% m/m foram avaliadas. As variáveis de saída, tais como: a temperatura da superfície do filme (Ts), a espessura de filme (?), a taxa de evaporação efetiva (GE), o fluxo mássico de destilado (D), a velocidade radial (?r), a concentração de pseudocomponente "a" (Xa) e a conversão (?) foram calculadas através da análise dos efeitos das condições operacionais definidas como sendo: a temperatura do evaporador (EVT), a vazão de alimentação (Q), a porcentagem de catalizador (%CAT), a temperatura de alimentação (Tfeed), a temperatura do condensador (Tcond), a velocidade do rotor (RS) e a pressão do sistema (PS). Os resultados mostraram que as variáveis de entrada, tais como a temperatura do evaporador (EVT) e a porcentagem de catalisador (%CAT) são as condições operacionais de maior influência sobre a composição final do fluxo do condensado. A concentração do pseudocomponente "i" diminui nas direções -s e -r, devido ao aumento da temperatura nas camadas internas do filme líquido. Por conseguinte, a espessura do filme diminui rapidamente ao longo da superfície do evaporador, enquanto que a quantidade de destilado aumenta continuamente ao longo do evaporador às condições operacionais seleccionadas. Resultados obtidos das simulações apresentaram uma conversão da carga de 65.6% no destilado e de 49,6% no resíduo, considerando uma porcentagem de 3% m/m de catalisador na carga inicial e uma temperatura de processo de 483,15 K. As predições oriundas da simulação foram comparadas com os dados experimentais e indicaram um desvio relativo percentual médio menor do que 6,82%; 9,39% e 14,92% para a taxa global de destilado, conversão na corrente de destilado e conversão na corrente de resíduo, respectivamente, o que é valioso, considerando-se a complexidade do processo e da mistura. Assim, o modelo desenvolvido mostrou-se adequado para descrever os processos de reação - separação na destilação molecular centrífuga reativa fornecendo orientação teórica para o desenvolvimento experimental e a futura otimização do processo. Por fim, o salto tecnológico em matéria computacional e experimental da DMCR concluiu em um efetivo desempenho do processo obtendo produtos com características favoráveis para os processos de exploração, escoamento, transporte e refino desde que: (i) mudanças importantes na fração analítica >613,15 K foram reportadas nas correntes de destilado atingindo uma conversão do ATR-W 673,15 K+ superior a 64.3%, valores de grau API entre 19 e 21 e massa molar até 200 kg·kmol-1, e (ii) foram observadas alterações significativas nas frações analíticas >613,15 K e >813.15 K nas correntes de resíduo, atingindo uma conversão do ATR-W 673,15 K+ entre 8.0% e 53.1%, valores de grau API aproximadamente iguais a 11,9 e massa molar entre 2570 kg·kmol-1 - 2908 kg·kmol-1 / Abstract: The reactive molecular distillation process, in which, the molecular distillation process and reactive process occur simultaneously can be characterized like an intensified and hybrid process due to the particular features on the equipment configuration which lead to use higher vacuum (<50 Pa), to keep the material inner the equipment with a short operational residence time, and to achieve a very intensive contact among the sample and catalytic surface. This work focuses mainly on the mathematical modeling and numerical simulation of centrifugal reactive molecular distillation process (CRMD - using heterogeneous catalysis) based on mathematical description of the centrifugal molecular distillation from high-boiling-point petroleum fractions. The computational case study illustrated was a 673.15 K+ high-boiling-point petroleum fraction of "W" crude oil (atmospheric residue ATR-W) with API gravity equals 11.9 and molar mass equals 2956 kg·kmol-1. The model and simulations were described at the steady-state conditions. A set of (11+18N) equations and (27+19N) variables were processed by the computational program named DESTMOL-R developed in FORTRAN-90 language using Compaq Visual Fortran compiler (professional edition 6.6). The system equations formulated inner the thin liquid film, along the evaporator surface, was numerically solved by the numerical method of lines. The process temperature (evaporator temperature) from 473.15 K to 523.15 K and the influence of adding a zeolite-based catalyst (regenerated catalyst used for FCC technology) between 3 and 5 %wt were examined. The output variables, such as the surface temperature (Ts), film thickness (?), effective evaporation rate (GE), distillate mass flow rate (D), radial velocity (?r), concentration of pseudocomponent "a" (Xa) and the conversion degree (?) profiles, were computed by analyzing the effects of the operational conditions (the evaporator temperature (EVT), feed flow rate (Q), percent weight of catalyst (%CAT), feed temperature (Tfeed), condenser temperature (Tcond), rotor speed (RS) and the system pressure (Ps)). Results showed that the inlet variables such as the evaporator temperature (EVT) and the weight percent of catalyst (%CAT) are the most suitable operating conditions into the final composition of the condensate flow. The concentration of the pseudocomponent "i" shrinks in both s- and r- directions, due to the fast increase of the temperature in the thin liquid film. Consequently, the thickness of the film rapidly decreases in this region, whereas the amount of the distillate of the split molecules continuously increases along the evaporator at the selected operating conditions. Simulated data indicated a conversion equal to 49.6% of feedstock in the residue stream and 65.6% of feedstock in the distillate stream when considered 3 wt% of catalyst and an evaporator temperature (EVT) equals 483.15 K. The simulated results agree well with those obtained by the experimental study, indicating the accuracy and reliability of the mathematical model since the average percent error was no larger than 6.82%, 9.39% and 14.92% for the distillate flow rate, extent conversion in the distillate rate and in the residue stream, respectively. It can be concluded that the mathematical model can describe the reaction - split processes in the CRMD process providing theoretical guidance for the further experimental runs and process optimization. Finally, the technological leap in the computational and experimental exercises of the CRMD process concluded in an effective performance of the process obtaining products with favorable characteristics for exploration, flow, transport and refining processes since: (i) important changes in the >613.15 K analytical fraction were reported in the distillate stream reaching a conversion of the ATR-W 673.15 K+ higher than 64.3%, values of API gravity between 19-21 and molar mass up 200 kg·kmol-1, and (ii) significant changes were found in the >613.15 K and >813.15 K analytical fractions of the residue streams, reaching a conversion of the ATR-W 673.15 K+ between 8.0 and 53.1%, values of API gravity approximately equal to 11.9 and molar mass between 2570 kg·kmol-1 - 2908 kg·kmol-1 / Doutorado / Desenvolvimento de Processos Químicos / Doutor em Engenharia Química

The PHD thesis is focused on the absorption with chemical reaction on the pilot plant gas/liquid scrubber. The performance characterization of the apparatus is based on the absorption of carbon dioxide in to the 1\% sodium hydroxide sollution and includes pressure drops, liquid holdup, gas/liquid contact time and the capture effectiveness as well. The experimantal part of the thesis includes a complex of mathematical equations based on the Film theory. The complex of the mathematical equations allowed a calculation of the overall mass transfer coefficient for the type of the gas scrubber at the given experimental conditions.

This thesis develops various aspects of Algebraic Geometry and its applications in different fields of science. In Chapter 2 we characterise the feasible set of an optimisation problem relevant in chemical process engineering. We consider the polynomial dynamical system associated with mass-action kinetics of a chemical reaction network. Given an initial point, the attainable region of that point is the smallest convex and forward closed set that contains the trajectory. We show that this region is a spectrahedral shadow for a class of linear dynamical systems. As a step towards representing attainable regions we develop algorithms to compute the convex hulls of trajectories. We present an implementation of this algorithm which works in dimensions 2,3 and 4. These algorithms are based on a theory that approximates the boundary of the convex hull of curves by a family of polytopes. If the convex hull is represented as the output of our algorithms we can also check whether it is forward closed or not. Chapter 3 has two parts. In this first part, we do a case study of planar curves of degree 6. It is known that there are 64 rigid isotopy types of these curves. We construct explicit polynomial representatives with integer coefficients for each of these types using different techniques in the literature. We present an algorithm, and its implementation in software Mathematica, for determining the isotopy type of a given sextic. Using the representatives various sextics for each type were sampled. On those samples we explored the number of real bitangents, inflection points and eigenvectors. We also computed the tensor rank of the representatives by numerical methods. We show that the locus of all real lines that do not meet a given sextic is a union of up to 46 convex regions that is bounded by its dual curve. In the second part of Chapter 3 we consider a problem arising in molecular biology. In a system where molecules bind to a target molecule with multiple binding sites, cooperativity measures how the already bound molecules affect the chances of other molecules binding. We address an optimisation problem that arises while quantifying cooperativity. We compute cooperativity for the real data of molecules binding to hemoglobin and its variants. In Chapter 4, given a variety X in n-dimensional projective space we look at its image under the map that takes each point in X to its coordinate-wise r-th power. We compute the degree of the image. We also study their defining equations, particularly for hypersurfaces and linear spaces. We exhibit the set-theoretic equations of the coordinate-wise square of a linear space L of dimension k embedded in a high dimensional ambient space. We also establish a link between coordinate-wise squares of linear spaces and the study of real symmetric matrices with degenerate eigenspectrum.

Due to the ever increasing concerns about pollutants and contaminants found in water, new treatment technologies have been developed. Ozonation is one of such technologies. It has been widely applied in the treatment of pollutants in water and wastewater treatment processes. Ozone has many applications such as oxidation of organic components, mineral matter, inactivation of viruses, cysts, bacteria, removal of trace pollutants like pesticides and solvents, and removal of tastes and odours. Ozone is the strongest conventional oxidant that can result in complete mineralisation of the organic pollutants to carbon dioxide and water. Because ozone is unstable, it is generally produced onsite in gas mixtures and is immediately introduced to water using gas/liquid type reactors (e.g. bubble columns). The ozone reactions are hence of the type gas liquid reactions, which are complex to model since they involve both chemical reactions, which occur in the liquid phase, and mass transfer from the gas to the liquid phase. This study focuses on two aspects: mass transfer and chemical reactions in multicomponent systems. The mass transfer parameters were determined by experiments under different conditions and the chemical reactions were studied using single component and multicomponent systems. Two models obtained from the literature were adapted to the systems used in this study. Mass transfer parameters in the semi-batch reactor were determined using oxygen and ozone at different flow rates in the presence and absence of t-butanol. t-Butanol is used as a radical scavenger in ozonation studies and it has been found to affect the gas-liquid mass transfer rates. An experimental study was carried out to investigate the effects of t-butanol concentrations on the physical properties of aqueous solutions, including surface tension and viscosity. It was found that t-butanol reduced both properties by 4% for surface tension and by a surprising 30% for viscosity. These reductions in the solution physical properties were correlated to enhancement in the mass transfer coefficient, kL. The mass transfer coefficient increased by about 60% for oxygen and by almost 50% for ozone. The hydrodynamic behaviour of the system used in this work was characterised by a homogeneous bubbling regime. It was also found that the gas holdup was significantly enhanced by the addition of t-butanol. Moreover, the addition of t-butanol was found to significantly reduce the size of gas bubbles, leading to enhancement in the volumetric mass transfer coefficient, kLa. The multicomponent ozonation was studied with two systems, slow reactions when alcohols were used and fast reactions when endocrine disrupting compounds were used. ii These experiments were simulated by mathematical models. The alcohols were selected depending on their volatilization at different initial concentrations and different gas flow rates. The degradation of n-propanol as a single compound was studied at the lowest flow rate of 200 mL/min. It was found that the degradation of n-propanol reached almost 60% within 4 hours. The degradation of the mixture was enhanced with an increase in the number of components in the mixture. It was found that the degradation of the mixture as three compounds reached almost 80% within four hours while the mixture as two compounds reached almost 70%. The effect of pH was studied and it was found that an increase in pH showed slight increase in the reaction. Fast reactions were also investigated by reacting endocrine disrupting chemicals with ozone. The ozone reactions with the endocrine disrupters were studied at different gas flow rates, initial concentrations, ozone concentrations and pH. The degradation of 17β-estradiol (E2) as a single compound was the fastest, reaching about 90% removal in almost 5 minutes. However estrone (E1) degradation was the lowest reaching about 70% removal at the same time. The degradation of mixtures of the endocrine disruptors was found to proceed to lower percentages than individual components under the same conditions. During the multicomponent ozonation of the endocrine disruptors, it was found that 17β-estradiol (E2) converted to estrone (E1) at the beginning of the reaction. A MATLAB code was developed to predict the ozone water reactions for single component and multicomponent systems. Two models were used to simulate the experimental results for single component and multicomponent systems. In the case of single component system, good simulation of both reactions (slow and fast) by model 1 was obtained. However, model 2 gave good agreement with experimental results only in the case of fast reactions. In addition, model 1 was applied for multicomponent reactions (both cases of slow and fast reaction). In the multicomponent reactions by model 1, good agreement with the experimental results was also obtained for both cases of slow and fast reactions.

No description available.

La croissance de polymères bidimensionnels a été étudiée sous ultra-haut vide sur des surfaces métalliques par microscopie à effet tunnel (STM). La première étude concerne la croissance de réseaux nanoporeux covalents bidimensionnels obtenus par réaction de déshydratation des molécules d'acide 1.4 diboronique (BDBA). Les meilleurs réseaux sont obtenus pour les dépôts à flux élevés sur des substrats d'Argent chauffés à 150°C. La deuxième étude concerne la réaction chimique entre les molécules de 1,2,4,5 tétracyanobenzène (TCNB) et les atomes de Fer. La formation de liaison covalente entre les molécules et les atomes de Fer est thermiquement activée par des recuits à 200°C et permet la formation d'octacyanophtalocyanine de Fer. Ce travail ouvre de nouvelles perspectives pour la fabrication de matériaux 2D originaux obtenus par des réactions chimiques de surface. / The growth of two dimensional polymers has been studied under ultra-high vacuum on metallic surfaces by scanning tunnelling microscopy (STM). The first study relates on the growth of two dimensional covalent nanoporous networks obtained after dehydratation reaction of the 1,4 diboronic acid benzene molecule (BDBA). The best networks have been obtained with high molecular flux on silver metallic substrates maintained at 150°C during deposition. The second study relates on chemical reaction between the 1, 2, 4, 5 tetracyanobenzene molecule (TCNB) and iron atoms. The reaction takes place after an annealing at 200°C. In that case some iron octacyanophthalocyanine have been successfully synthesised at surfaces. This work opens new perspectives for the fabrication of 2D original materials by chemical reactions on surfaces.

Les méthodes Direct Simulation Monte Carlo (DSMC) sont utilisées par Ariane group pour calculer les torseurs d'efforts aérodynamiques et les flux thermiques sur les engins spatiaux pour des écoulements hypersoniques en milieu raréfié.Afin de pouvoir caractériser la dislocation des étages de lanceurs et donc l'empreinte de retombée de débris, une modélisation précise des mécanismes générateurs de flux thermiques est nécessaire. Les réactions chimiques étant dimensionnantes pour le calcul du flux thermique, l'objectif de cette thèse est de développer l'outil de calcul avec la méthode DSMC nommé IEMC de manière à pouvoir prendre en compte les écoulements réactifs.Deux modèles de chimie sont mis en place pour pouvoir prendre en compte la totalité des réactions. Après leur vérifications sur des cas élémentaires, ils sont appliqués et validés sur des cas tests de rentrée pour différentes atmosphères. Les différents modèles considérés sont testés afin d'évaluer leur influence. Les modèles de chimie dépendent de nouveaux paramètres d'entrée, dont les valeurs numériques sont incertaines. Une étude de quantification de leur incertitude est menée et a permis de vérifier que les grandeurs de sorties de la simulation avec un écoulement réactif, notamment le flux thermique, n'est que peu impacté par ces paramètres incertains. / Direct Simulation Monte Carlo (DSMC) methods are used in Ariane group to compute aerodynamic forces and moments and heat fluxes on space objects for hypersonic flows in rarefied regimes.To caracterise the dislocation of the stages and the debris footprints, a precise modelisation of the mechanism that contribute to the heat flux is necessary. The contribution of the chemical reactions is important for the determination of the heat flux. The purpose of this thesis is to develop the in house IEMC tool using the DSMC method so that it can compute reactive flows.The different steps of the developments are presented in this work. The first step is the presentation, implementation and verification of two different chemistry models. They are validated for simulations on real test cases. Different models are tested in order to evaluate their effect. Chemical models implemented in the code depend on new input parameters, whose numerical data are uncertain. Using a uncertainty quantification study, it is shown that the output data of the reactive simulation, especially the heat flux, is weakly impacted by the tested uncertain parameters.