L’élimination des inclusions indésirables par flottation en cuve agitée est un procédé largement utilisé dans l’industrie de l’aluminium. Ce procédé consiste en l’injection de gaz au sein de la cuve par le biais d’un rotor ; les bulles ainsi formées captent, lors de leur ascension dans le métal liquide, les inclusions et les drainent en surface où elles sont éliminées mécaniquement.Dans le but de prédire l’évolution numérale de la population d’inclusions dans la cuve de flottation au cours du temps, un modèle 2D a été développé. Afin de rendre compte du transport convectif des inclusions au sein de l’écoulement diphasique métal liquide – bulles, des phénomènes de décantation, d’agglomération et de flottation, ce modèle couple la Mécanique des Fluides Numérique et la technique des Bilans de Population. Une attention particulière a été portée aux modèles d’agglomération et de flottation pour qu’ils soient applicables sur une grande plage de conditions de turbulence.Les simulations numériques réalisées, nous ont notamment permis de mettre en évidence l’importance de veiller à une bonne répartition des bulles dans la cuve, en particulier dans les zones de forte turbulence. En parallèle de ce travail de modélisation, une analyse de la littérature et des travaux expérimentaux sur métal liquide ont été réalisés, afin de mieux comprendre le rôle du chlore dans le procédé de flottation. Un effet de seuil a ainsi pu être mis en évidence : une certaine quantité de chlore injectée dans le métal est nécessaire pour que la flottation devienne efficace. La compréhension du rôle du chlore reste cependant partielle, mais des pistes de recherche prometteuses ont put être identifiées / Inclusions removal by flotation in mechanically agitated vessels is widely used in liquid aluminium treatments. This process consists of gas injection in a molten aluminium reactor using an impeller. Inclusions are attached to the bubbles while rising into the liquid bulk and released in the froth at the vessel surface.With the aim of both a better understanding of the physical processes acting during flotation and the optimization of the refining process, a 2D mathematical modelling of the flotation tank was set up. Transport phenomena, sedimentation, agglomeration and flotation of inclusions were considered here. The model couples Population Balance with convective transport of the inclusions, in the multiphase flow field. Simulations showed that a good dispersion of the bubbles into the tank, especially in the high turbulence zones, is essential for an efficient process. This situation was achieved with a strong agitation. Gas flow affected the process efficiency weakly.Theoretical and experimental studies on chlorine effects were done. It was noticed that a critical amount of chlorine into the melt is required for the flotation to be efficient. Complete understanding of chlorine role is not achieved yet, but promising ideas for future research have been exhibited

La mécanique des fluides numérique (CFD) est utilisée pour modéliser la précipitation du carbonate de baryum dans un réacteur à lit fluidisé. L’étude est divisée en deux parties : la modélisation de l’hydrodynamique du réacteur et la modélisation de la précipitation du carbonate de baryum. Pour ces deux parties, les modèles sont validés par l’expérience. Dans la première partie de l’étude, des réactions instantanées de neutralisation en absence et en présence de particules solides inertes sont mises en œuvre dans le réacteur à lit fluidisé. Pour représenter la réaction chimique dans la phase liquide, plusieurs modèles son testés : le modèle Eddy Dissipation (EDM), le modèle Eddy Dissipation Concept (EDC) et le modèle modifié Eddy Dissipation- Multiple Time Scale turbulent mixer (EDM-MTS). Le modèle qui donne la meilleure prédiction de la réaction chimique est choisi : il s’agit du modèle EDM-MTS, qui demande aussi le moins de temps de calcul. Dans la deuxième partie, l’équation de bilan de population est incorporée au code de calcul pour prédire la distribution de taille des particules (PSD). La méthode des classes est implémentée couplée avec le modèle des écoulements multiphasiques Eulérien-Eulérien, le modèle de turbulence k-e et le modèle EDM-MTS. Les cinétiques de précipitation de BaCO3 sont incluses dans le modèle. Des expériences de précipitation du BaCO3 en réacteur à lit fluidisé permettent de valider le modèle de CFD développé. La PSD donnée par le modèle de CFD est en bonne concordance avec les résultats expérimentaux / Computational Fluid Dynamics (CFD) techniques are used to model the precipitation of Barium Carbonate in a solid-liquid fluidized bed reactor. The study is divided in two sections: The hydrodynamic behavior and the barium carbonate precipitation. The CFD model is validated with experimental results for both cases. In the first part, a neutralization reaction in the fluidized bed column with and without solids is carried out. In order to simulate the liquid phase reaction, the Eddy Dissipation Model (EDM), the Eddy Dissipation - Multiple Time Scale turbulent mixer model (EDM-MTS) and the Eddy Dissipation Concept (EDC) reaction models are tested. The model EDM-MTS is chosen for giving the best approach and for being the less computationally expensive. In the second part, the population balance equation is added to the model in order to calculate the Particle Size Distribution (PSD) in the fluidized bed reactor. The discrete method is chosen to solve the population balance equation coupled with the multi-phase Eulerian-Eulerian model, the k-e turbulence model and the EDM-MST model. The nucleation, growth and aggregation kinetics of BaCO3 are included in the precipitation model. The experimental BaCO3 precipitations realized in a fluidized bed reactor allowed the CFD precipitation model validation. The PSD obtained by CFD are in good agreement with the experimental PSD

La simulation devient un outil incontournable pour concevoir ou optimiser les procédés en biotechnologies. Elle est particulièrement pertinente pour permettre le changement d'échelle de l'échelle laboratoire à la mise en œuvre de cultures biologiques industrielles. Cette thèse se concentre sur le développement d'une structure de modèle pour les fermenteurs, qui ne néglige ni les problématiques de mélange, ni la complexité biologique, tout en permettant des simulations rapides. Pour intégrer l'ensemble des phénomènes couplés et dynamiques interagissant dans les bioréacteurs, l'approche proposée couple (i) un modèle métabolique dynamique pour décrire le comportement des cellules, (ii) un modèle de bilan de population pour suivre la diversité biologique et (iii) un modèle de compartiments pour décrire l'hydrodynamique du fermenteur. Une structure de modèle métabolique, générique et numériquement peu couteuse a été appliquée à E. coli et S. cerevisiae et été confrontée avec succès à de nombreuses données expérimentales. Parmi plusieurs méthodes numériques permettant de traiter les équations de bilan de population, la méthode EQMOM a été sélectionnée pour sa stabilité et sa précision et son coût a été réduit d'un facteur 10. L'hydrodynamique gaz-liquide d'un fermenteur industriel a été obtenue par simulations CFD et des outils ont été développés pour en extraire des modèles de compartiments. Le couplage de ces différents aspects a finalement été illustré par la simulation d'une culture industrielle. Ce travail ouvre la voie à la création d'outil de simulation rapide, ce qui permettra des études d'ingénierie de design et d'optimisation de procédés industriels. / Simulations are becoming an essential tool to design and improve processes in the field of biotechnologies. They are especially relevant to facilitate the scale-up of biological cultures from laboratory to industrial scales which is a key difficulty as of now. This thesis focuses on developping a model structure for fermenters, which does not neglect either mixing issues known to occur in industrial bioreactor, nor biological complexity inherent to micro-organisms, while enabling fast and low-cost simulations. To account for all coupled and dynamic phenomena that occur in bioreactors, the developed approach couples (i) a dynamic metabolic model to describe cells behaviour, (ii) a population balance model tracking biological cell-to-cell diversity and (iii) a compartment model to account for fermenter hydrodynamics. A structure for low-cost dynamic metabolic model has been developed, applied to E. coli and S. cerevisiae and successfully challenged against experimental data. Among multiple numerical methods tackling population balance equations, the EQMOM method has been selected for its stability and precision, and its algorithm has been improved by reducing its cost by a factor 10. The gas-liquid hydrodynamics of an industrial fermenter has been obtained through CFD simulations, and tools have been developed to extract compartment model from these simulation results. Finally, the coupling between all these modeling blocks has been demonstrated by simulating an actual industrial culture. This work paves the way to the emergence of fast bioreactor simulation tools, which will then enable new enginnering studies for designing and optimising industrial bio-processes.

Nanoparticles are used in various applications like medical diagnostics, drug delivery, energy technology, electronics, catalysis etc. Although particles of such small dimensions can be synthesized through various methods, the liquid phase synthesis methods stands out for their simplicity. Typically, these methods involve reaction of precursors to form solute. At high concentration of solute, nucleation commences and nuclei are formed. These nuclei grow in size by assimilating solute from the bulk. Stabilizers or capping agents compete with solute for adsorption on the surface of a growing particle. Two partially protected particles can form bigger particle by coagulation. Uncontrolled turbulent flow field in laboratory scale reactors combined with all the above quite fast and poorly understood steps often lead to poorly controlled synthesis of particles. In many a systems, it also leads to very poor reproducibility. Any attempt to synthesis nanoparticles at engineering scale, with good control on mean size and polydispersity, requires quantitative understanding of the synthesis process. It can then be combined with description of other transport processes in reactors to optimize synthesis protocols. Two main factors hinder progress in this direction: complex and often poorly understood chemistry, and inefficient tools to simulate particle synthesis. In the first part of the thesis, a quantitative model is developed for tannic acid method of synthesis of gold nanoparticles. It showcases the approach used to model a system with poorly understood chemistry and which defies an understanding through the widely used homogeneous nucleation based mechanism for particle synthesis. An organizer based mechanism in which tannic acid brings together nucleating species to facilitate nucleation is invoked. Simple reaction network based models however fail to explain the experimental findings. The underlying chemistry is explored to develop a comprehensive reaction network. This network is used as a guide to seek pathways which can mimic burst of nucleation, a characteristic of homogeneous nucleation based mechanism, through self-limiting nucleation, and various other features present in the experimental data. After successful prediction of all the features of the experimental data through this network, a minimal organizer based mechanism which leads to self-limiting nucleation is developed. The minimal organizer model offers itself as a competing and alternative mechanism to explain nanoparticle synthesis. A few new predictions made by the new model are verified by others in our group. Monte-Carlo (MC) simulations are used as a powerful tool to simulate stochastic processes. Their application to nanoparticle synthesis is limited by three problems: (i) zero initial rate of stochastic processes which leads to infinite time step at the beginning of the simulation, (ii) sensitively time dependent rate of stochastic processes, and (iii) computation intensive simulations. We propose a new approach to carry out MC simulations. It makes use of simulation results obtained with systems of extremely small sizes. These system size dependent predictions, obtained at substantially reduced computational cost are used to construct results for system of infinite size. The approach is based on a new power law scaling that we have found in this work. An efficient implementation of MC simulation for time dependent rate processes is also developed. In this method, an additional variable is introduced for inter-event evolution. It increases the number of differential equation by one, but significantly reduces the computational effort required to estimate the interval of quiescence for time dependent rate processes. All the above ideas are combined in the new approach to simulate complete size distribution for simultaneous nucleation and growth of nanoparticles for a system of infinite size from erroneous simulations carried out with three extremely small size systems. A new framework for solving multidimensional population balance equations (PBEs) which routinely arise in modeling of nanoparticle synthesis is also developed. The new framework advances the concept of minimal internal consistency of discretization. It suggests that an n dimensional PBE is a statement of evolution of population of particles while accounting for how n internal attributes of particles change in particulate events. Thus, a minimum of n + 1 attributes of particles, instead of 2n attributes used hitherto, need to be represented perfectly in discrete representation. This is termed as the concept of minimum internal consistency of discretization in this work. The elements used for discretization should therefore be triangles for 2-d, tetrahedrons for 3-d, and an object with n + 1 vertices in n-d space for the solution of a n-d PBE. The results presented for the solutions for 2-d and 3-d PBEs show the superiority of this framework over the earlier framework. The present work also shows that directionality of elements plays a critical role in the solution of multi-dimensional PBEs. A mere change in connectivity of pivots in space, which changes their directionality, is shown to influence numerical results. This work led to new radial discretization of space, which has been followed up by others in the group and demonstrated to be quite powerful. A physical model is developed to understand digestive ripening of nanoparticles, a technique which is in extensive use in the literature to improve monodispersity of nanoparticles. The physical model is based on critical analysis of the large body of experimental findings available in the literature on several variations of this technique. The physical model is the first one to consistently and qualitatively explain all the reported experimental findings.

This thesis has made two significant contributions to the field of reactive crystallisation. First, new data from batch cooling crystallisation and semi-batch reactive crystallisation experiments of mono-ammonium phosphate (MAP) were obtained to describe the key factors that influence crystal nucleation and growth rates, crystal size distribution (CSD), and crystal shape. The second contribution is the development of a numerical scheme for solving the population balance equations, which can be used to describe the evolution of CSD during the crystallisation process. This scheme combines the finite difference method with a wavelet method, and is the first reported application of this approach for crystallisation modelling and simulation. / Experiments into the batch cooling crystallisation of MAP were conducted both with and without seed crystals. The effects of key factors such as cooling rate, initial level of supersaturation and seeding technique, including seed concentration and seed size, on the real time supersaturation, final CSD, crystal yield and crystal shape were investigated. It was found that a seed concentration of 20-30% effectively suppressed nucleation. The growth and nucleation rate were estimated by using an isothermal seeded batch approach and their parameters were calculated by non-linear optimisation techniques. / The second series of experiments involved the semi-batch reactive crystallisation of MAP. Both single-feed and dual-feed systems were investigated. In the single-feed arrangement, an ammonia solution was fed into a charge of phosphoric acid. In the dual-feed system, phosphoric acid and ammonia solution were fed into a charge of saturated MAP solution. The molar ratio of the reactants, initial supersaturation, presence or absence of seed crystals, initial MAP concentration, reactants’ flow rate, feeding time and stirring speed were varied, and the effects upon the real time supersaturation, final CSD, crystal yield, crystal shape and solution temperature were measured. X-ray diffraction analysis showed that MAP can be produced in both the single-feed and dual-feed arrangements. For the single feed system, the N/P mole ratio controlled the degree of reaction and the CSD of the product. Di-ammonium phosphate (DAP) was not be observed in the single-feed system due to its high solubility. In the dual-feed system, a seeded solution with slow feed addition, moderate stirring speed and a low initial supersaturation provided the most favourable conditions for generating a desirable supersaturation profile, and thus obtaining a product with good CSD and crystal shape. / A comparative numerical study was undertaken in order to evaluate the existing numerical schemes for solving the population balance equations (PBE) that describe crystallisation. Several analytical solutions to the PBE were used to benchmark the following numerical schemes: Upwind Finite Difference, Biased Upwind Finite Difference, Orthogonal Collocation with Finite Elements, and Wavelet Orthogonal Collocation. The Wavelet Finite Difference (WFD) method has been applied here for the first time for solving PBE problems. The WFD scheme was adapted to solve the batch cooling and the semi-batch reactive crystallisation models, and the solutions were validated against experimental data that we obtained. / In summary, the experimental data provide an improved understanding of MAPreaction and crystallisation mechanisms. The adaptability of the WFD method has beendemonstrated validating the two crystallisation systems, and this should help extendthe application of wavelet-based solutions beyond crystallisation processes and intomore diverse areas of chemical engineering.

Milling is a common unit operation in industry for the purpose of intentional size reduction. Considerable amount of energy is consumed during a grinding process and much of the energy is dissipated as heat and sound, which often makes grinding into an energy-intensive and highly inefficient operation. Despite many attempts to interpret particle breakage during a milling process, the grindability of a material in a milling operation remains aloof and the mechanisms of particle breakage are still poorly understood. Hence the optimisation and refinement in the design and operation of milling are in great need of an improved scientific understanding of the complex failure mechanisms. This thesis aims to provide an in-depth understanding of particle breakage associated with stressing events that occur during milling. A hybrid of experimental, theoretical and numerical methods has been adopted to elucidate the particle breakage mechanics. This study covers from single particle damage at micro-scale to bulk comminution during the whole milling process. The mechanical properties of two selected materials, i.e. alumina and zeolite were measured by indentation techniques. The breakage test of zeolite granules subjected to impact loading was carried out and it was found that tangential component velocity plays an increasingly important role in particle breakage with increasing impact velocity. Besides, single particle breakage via in-situ loading was conducted under X-ray microcomputed tomography (μCT) to study the microstructure of selected particles, visualize the progressive failure process and evaluate the progressive failure using the technique of digital image correlation (DIC). A new particle breakage model was proposed deploying a mechanical approach assuming that the subsurface lateral crack accounts for chipping mechanism. Considering the limitation of existing models in predicting breakage under oblique impact and the significance of tangential component velocity identified from experiment, the effect of impact angle is considered in the developed breakage model, which enables the contribution of the normal and tangential velocity component to be rationalized. The assessment of breakage models including chipping and fragmentation under oblique impact suggests that the equivalent normal velocity proposed in the new model is able to give close prediction with experimental results sourced from the public literature. Milling experiments were performed using the UPZ100 impact pin mill (courtesy by Hosokawa Micron Ltd. UK) to measure the comminution characteristics of the test solids. Several parameters were used to evaluate the milling performance including product size distribution, relative size span, grinding energy and size reduction ratio etc. The collective data from impact pin mill provides the basis for the validation of numerical simulation results. The Discrete Element Method (DEM) is first used to model single particle breakage subject to normal impact loading using a bonded contact model. A validation of the bonded contact model was conducted where the disparity with the experimental results is discussed. A parametric study of the most significant parameters e.g. bond Young’s modulus, the mean tensile bond strength, the coefficient of variation of the strength and particle & particle restitution coefficient in the DEM contact model was carried out to gain a further understanding of the effect of input parameters on the single particle breakage behavior. The upscaling from laboratory scale (single particle impact test) to industrial process scale (impact pin mill) is achieved using Population Balance Modelling (PBM). Two important functions in PBM, the selection function and breakage function are discussed based on the single particle impact from both experimental and numerical methods. An example of predicting product size reduction via PBM was given and compared to the milling results from impact pin mill. Finally, the DEM simulation of particle dynamics with emphasis on the impact energy distribution was presented and discussed, which sheds further insights into the coupling of PBM and DEM.

In some species, including humans, red blood cells (RBCs) under low shear stress tend to clump together and form into regular stacks called rouleaux. These stacks are not static, and constantly move and break apart. This phenomenon is referred to as red blood cell aggregation and disaggregation. When modelled as a single liquid, blood behaves as a non-Newtonian fluid. Its viscosity varies, mainly due to the aggregation of RBCs. The aim of this research is to develop a mesoscale computational model for the simulation of RBCs in plasma. This model considers RBC interaction and aggregation to predict blood-flow characteristics such as viscosity, rouleaux size and velocity distribution. In this work, the population-balance modelling (PBM) approach is utilized to model the RBC aggregation process. The PBM approach is a known method that is used for modelling agglomeration and breakage in two-phase flow fluid mechanics to find aggregate size. The PBM model is coupled to the incompressible Navier-Stokes equations for the plasma. Both models are numerically solved simultaneously. The population-balance equation has been used previously in a more restricted form, the Smoluchowski equation, to model blood viscosity, but it has never been fully coupled with the Navier-Stokes equation directly for the numerical modelling of blood flow. This approach results in a comprehensive model which aims to predict RBC aggregate size and their velocities for different flow configurations, as well as their effects on the apparent macro-scale viscosity. The PBM approach does not treat the microscopic physics of aggregation directly but rather uses experimental correlations for aggregation and disaggregation rates to account for the effects of aggregation on the bulk. To find the aggregation rate, a series of experiments on RBC sedimentation due to gravity is designed. In these tests, aggregated RBCs (rouleaux) tend to settle faster than single RBCs and, due to low shear stresses, disaggregation is very low and can be neglected. A high-speed camera is used to acquire video-microscopic pictures of the process. The size of the aggregates and their velocities are extracted using image processing techniques. For image processing, a general Matlab program is developed which can analyze all the images and report the velocity and size distribution of rouleaux. An experimental correlation for disaggregation rate is found using results from a previous steady-state Couette flow experiment. Aggregation and disaggregation rates from these experiments are used to complete the PBM model. Pressure-driven channel flow experiments are then used for the final validation of the model. Comparisons of the apparent viscosity of whole blood in previous experiments show reasonable agreement with the developed model. This model fills a gap between micro-scale and macro-scale treatments and should be more accurate than traditional macro-scale models while being cheaper than direct treatment of RBCs at the micro-scale.

Orientador: Eduardo Augusto Caldas Batista / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia de Alimentos / Made available in DSpace on 2018-08-16T00:41:25Z (GMT). No. of bitstreams: 1 Sanaiotti_Guilherme_M.pdf: 2559183 bytes, checksum: 49e8656b4f14ee53f65b1a0dc45c232d (MD5) Previous issue date: 2010 / Resumo: A desacidificação de óleos vegetais por extração líquido-líquido apresenta-se como uma alternativa atraente às elevadas perdas e gastos energéticos usualmente encontrados nos métodos de refino alcalino e por destilação de ácidos graxos livres, respectivamente. A utilização de insumos provenientes de fontes renováveis e a ausência de geração de resíduos conferem ainda caráter ambiental pertinente ao processo. Modelos descritivos de perfis axiais de composição de fases, fundamentados em balanços populacionais de gotas e transferência de massa multicomponente, são essenciais para o desenvolvimento de métodos de design e scale up de colunas de extração líquido-líquido. A principal finalidade deste trabalho foi avaliar correlações, métodos e diretrizes para o dimensionamento de colunas de discos rotativos aplicadas à desacidificação de óleo de soja. Dados de composições de fases em equilíbrio, densidades, viscosidades e tensões interfaciais de sistemas compostos por óleo de soja + ácido linoléico comercial + etanol + água a 298,2 K foram determinados experimentalmente a frações mássicas de água no solvente iguais a 5,00 %, 8,00 %, 11,00 % e 14,00 %. Os desvios relativos absolutos entre os valores experimentais e os estimados por meio de equações empíricas foram inferiores a 6,36 %. Perfis de composição de fases quantificados por 3 diferentes modelos foram correlacionados a dados experimentais existentes na literatura, determinados em uma coluna de discos rotativos (RDC) com 5,0 cm de diâmetro, utilizada para a desacidificação de óleo de milho. Os desvios relativos absolutos entre as frações mássicas de ácidos graxos livres experimentais e as obtidas por simulação foram próximos a 20 %. Em um estudo hipotético, colunas de discos rotativos foram dimensionadas sob diferentes condições operacionais e teores de água no solvente, ao se considerar vazões mássicas de óleo de soja bruto equivalentes a 11,488 ton¿h-1. Os fatores avaliados apresentaram efeito significativo sobre as dimensões calculadas, ao obterem-se diâmetros de coluna compreendidos entre 2,29 m e 2,94 m, bem como alturas de zona de extração entre 5,89 m e 69,07 m. Para sistemas compostos por óleos vegetais + ácidos graxos livres + etanol + água, os efeitos das variáveis operacionais de colunas mecanicamente agitadas sobre os perfis de tamanhos de gotas e de composições de fases são ainda pouco elucidados. Desta forma, este estudo revela-se de grande importância para a efetiva inserção dessa alternativa de processo no refino de óleos vegetais, ao proporcionar com que os métodos de design e scale up elevem-se a patamares quantitativamente mais precisos / Abstract: Deacidification of vegetable oils by liquid-liquid extraction seems to be an attractive alternative to high oil losses and energy costs typically found in alkali refining and by distillation of free fatty acids, respectively. The use of raw materials attained from renewable sources and the absence of residuals provides also a relevant environmental feature to the process. Descriptive models of phase composition profiles, based on drop population balances and multicomponent mass transfer, are essential for the development of design and scale up methods of liquid-liquid extraction columns. The major aim of this work was to evaluate correlations, methods and guidelines for sizing rotating disc columns applied to soybean oil deacidification. Equilibrium phase compositions, densities, viscosities and interfacial tensions for systems composed of soybean oil + commercial linoleic acid + ethanol + water at 298.2 K were experimentally determined using alcoholic solvents with water mass fractions of (5.00, 8.00, 11.00 and 14.00) %. The relative absolute deviations between experimental data and those calculated from empirical equations were lower than 6.36 %. Phase compositions profiles, quoted using 3 different models, were correlated to experimental data described in literature, determined in a rotating disc column (RDC) with 5.0 cm in diameter, which was used for corn oil deacidification. The relative absolute deviations between the free fatty acid mass fractions experimentally determined and those calculated from simulation were around 20 %. In a hypothetical study, rotating disc columns were sized for different operational conditions and water mass fractions in the solvent, considering crude soybean oil mass flow rates of 11.488 ton¿h-1. The studied factors were significant in the calculated dimensions, once the column diameters varied from (2.29 to 2.94) m and the column heights ranged from (5.89 to 69.07) m. For systems composed of vegetable oils + free fatty acids + ethanol + water, the effects of operational conditions of mechanically stirred columns on drop size and phase compositions profiles are still not well elucidated. Thus, this work becomes of great importance in the effective application of this alternative process in vegetable oils refining, shifting of column design and scale up methods to a quantitatively more precise level / Mestrado / Mestre em Engenharia de Alimentos

La règle des phases d'Ostwald classiquement utilisée pour justifier la cristallisation d'un système polymorphique, stipule que la phase métastable apparait en premier puis subit une transition polymorphique vers la phase stable. Les modèles classiques, qui ne considèrent que la nucléation et la croissance, ne permettent pas de refléter l'avantage cinétique de la phase métastable formulé par la règle d'Ostwald. Cette étude propose d'étudier et de mieux comprendre la cristallisation d'un système polymorphe en prenant en compte le mécanisme de mûrissement d'Ostwald, habituellement négligé. Un produit modèle, l'acide L-Glutamique, est choisi pour l'étude expérimentale menée en milieu agité et stagnant. Deux modèles, l'un basé sur les bilans de population, l'autre basé sur les équations cinétiques, sont développés et qualitativement comparés pour simuler le comportement expérimental des phases polymorphes. Alors que le modèle de bilan de population s'avère limité, le modèle des équations cinétiques a permis de souligner l'effet du mécanisme de mûrissement sur la compétition entre les phases polymorphes et de valider, ainsi, une nouvelle explication pour la règle des phases d'Ostwald / The Ostwald rule of stages is conventionally used to explain the crystallization behavior of a polymorphic system. It states that the metastable phase first appears and undergoes a polymorphic transition toward the stable phase, in a second step. The Classical models, which only consider nucleation and growth, fail to reflect the kinetic advantage of the metastable phase formulated by Ostwald’s rule. Hence, this work intends to study and better understand the crystallization of a polymorphic system, taking into account the Ostwald ripening mechanism, usually neglected. A model compound, L-Glutamic acid, is chosen for the experimental study in agitated and stagnant conditions. Two numerical models, one based on the population balance equation and the other based on the kinetic equations, are developed to simulate the behavior of that polymorphic system, observed experimentally. A qualitative comparison between these two models is proposed. The model that relates the population balance equation does not permit correct implementation of all the mechanisms. Conversely, the model based on the kinetic equations highlights the effect of the ripening mechanism on the competition between the two polymorphic phases and allows us to propose a new explanation of the Ostwald rule of stages

Un système consistant d'une simulation de mécanique des fluides numérique (MFN) couplée à un modèle de bilan de population (PBM) est développé afin d'étudier l'effet des paramètres variés sur la performance d'un procédé de polymérisation en émulsion qui conduit à la peoduction des particules de polymère dans un milieu aqueux continu.Comme une grande gamme des produits polymériques, des latexes sont les « produits par processus » (products-by-process), et leurs propriétés sont déterminés pendant la polymérisation. LA distribution de la taille des particules (PSD) est une des plus importants paramètres qui influence la qualité finale de latex. La modélisation d'évolution du PSD est généralement réalisée par l'addition un ensemble des PBEs au modèle cinétique. Le PBE fournit un moyen d'étudier la contribution des différents phénomènes dans l'évolution du PSD, comme la nucléation, la croissance des particules par la polymérisation, et la coagulation des particules à cause du mouvement brownien ou le mouvement du fluide (la coagulation Perikinetic et Orthokinetic, respectivement).Afin d'évaluer l'impact du mélange non homogène et les paramètres physiques du système sur l'évolution du PSD du latex, la simulation transitoire d'écoulement à été réalisé avec l'aide d'un progiciel commercial de MFN (Fluent® 15.0) pour munir dans chaque pas du temps, les concentrations locales des espèces ioniques (pour déterminer le taux de la coagulation Perikinetic modelé par le modèle de DLVO) ainsi que certains paramètres hydrodynamiques comme le taux de dissipation de la turbulence et le taux de cisaillement (afin de déterminer le taux de la coagulation Orthokinetic). Cette information est appliquée simultanément par le module complémentaire de PBM dans Fluent pour calculer le PSD pour le prochain pas du temps ; ainsi, un couplage complet entre le MFN et le PBM est assuré / A framework, consisting of a computational fluid dynamics (CFD) simulation model coupled to a population balance model (PBM) is developed to study the effect of various parameters on the performance of an emulsion polymerization process which leads to the production of a fine dispersion of polymer particles in a continuous aqueous medium.Like most polymer products, latexes are “products-by-process”, whose main properties are determined during polymerization. One of the main parameters influencing the final quality of the latexes is the particle size distribution (PSD). Modeling the evolution of PSD is usually accomplished through the addition of a set of PBEs to the kinetic model. PBE provides a means of considering the contribution of different phenomena in the PSD evolution, being nucleation, growth of polymer particles by polymerization, and coagulation of particles due to brownian or fluid motion (Perikinetic and Orthokinetic coagulation, respectively).To assess the impact of nonhomogeneous mixing and physical parameters of the system on the evolution of the latex PSD, the transient simulation of flow was performed with the aid of a commercial CFD Package (Fluent® 15.0) to provide in each time step, the local concentrations of ionic species (to determine the rate of perikinetic coagulation modeled by DLVO model) and certain hydrodynamic parameters such as turbulence dissipation rate and shear rate (to determine the rate of orthokinetic coagulation). This information is applied simultaneously by the PBE add-on module of Fluent to calculate the PSD for the next time step; thus a complete coupling between CFD and PBM is assured