Disponibilidade dos recursos energéticos junto com o despertar da consciência ambiental criaram um interesse por uma condição climática sensível compatível com os recursos disponíveis. Dentro desse cenário o trabalho se volta à necessidade de se criarem e manterem ambientes industriais termicamente adequados aos processos de produção para minimizar as interferências que as condições ambientais exercem sobre os custos dos processos de produtivos e sobre o consumo energético. Os sistemas de resfriamento evaporativo, por sua vez, têm sido a ferramenta de maior potencial de aplicação na criação de ambientes termicamente adequados aos processos. Este modelo revisto de conforto térmico nos coloca um passo à frente para o aumento eficiência energética na construção de projeto de climatização vinculados a temperaturas interiores que atendam conjuntamente tanto aos ocupantes como às atividades que desenvolvem no interior da área climatizada. Apesar de esse sistema apresentar vantagens operacionais, quando comparado a outros sistemas convencionais, existem certas limitações no seu desempenho. Uma das maiores dificuldades das instalações destes sistemas reside na existência de incertezas em qualquer resultado. Possibilitar um controle dos parâmetros, minimizando os erros de aplicação, evitando criar no ambiente um desconforto de tal grau que inviabilize sua aplicação, é o fundamento deste trabalho. A busca passa a ser pela garantia da aceitabilidade dos resultados do sistema projetado e seus limites de aplicabilidade. O estudo das variáveis que interferem no processo do resfriamento por micro aspersão permitiu desenvolver um processo que alterara esses parâmetros durante o funcionamento do sistema, interferindo, conforme a necessidade no seu desempenho, garantindo a completa evaporação da água micro aspergida. / Energy resources along with an environmental conscience awakening has created an interest in sensitive climate together with a more understanding regarding the use of available resources. Inside this scenario our work focus on the needs of creating and maintaining industrial environments thermally suited to these production processes that seeking to minimize interference that environmental conditions have on the costs of production processes and energy consumption. Evaporative cooling systems, in turn, has been a interesting tool to be used in the creation of thermally suitable environments to these processes. This new revised thermal comfort model puts us a step forward to increase energy efficiency in elaborating air treatment projects linked to indoor temperatures that meet both the occupants and the activities that develop inside the controlled area. Although this system has operational advantages when compared to other conventional systems, there are some limitations in their performance. A major difficulty of the installation envolving these systems is about the existence of uncertainty in any results. To allow the control of these parameters in order to minimize the errors in this kind of application and to avoid creating environmental discomfort to such a degree that prevent the implementation, it is the foundation of this work. The search is to ensure the acceptability of the results of the system designed and their limits of applicability. The study of the variables that affect the cooling process by misting allowed us to develop a process that altered these parameters during operation of the system, interfering, as required in its performance, ensuring complete evaporation of water applied by misting in the area.

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

Neste trabalho, estudos da copolimerização em emulsão de estireno e butadieno foram realizados em duas etapas. A primeira etapa consistiu na obtenção de um modelo matemático que representasse os processos em batelada e em semicontínuo através das principais variáveis do processo. Na segunda etapa, o efeito de diversas variáveis importantes ao processo foi avaliado, dentre elas: o tempo de adição dos reagentes, o tipo de alimentação empregado e a temperatura da reação. O modelo matemático se baseia em um trabalho previamente publicado que foi adaptado para simular o processo de copolimerização de estireno e butadieno em emulsão. Foram simulados processos em batelada e em semicontínuo. Em conjunto com os resultados experimentais, foi realizada a estimação de parâmetros não obtidos na literatura utilizando o método de Marquardt. As características do processo e as propriedades do polímero, tais como, conversão, diâmetro de partícula, taxa de polimerização e pressão interna do reator também foram obtidas, fornecendo condições para otimização e avaliação do processo de polimerização em batelada e em semicontínuo. Adicionalmente, também foi proposto um modelo de equilíbrio líquido-vapor dos monômeros. Os ensaios experimentais foram realizados em reator encamisado semicontínuo de mistura com 3 litros, nos quais foram utilizados persulfato de sódio como iniciador, lauril sulfato de sódio como emulsificante e tercdodecil mercaptana como agente de transferência de cadeia. Foram estudados os efeitos da temperatura, do tipo e do tempo de alimentação utilizada. A velocidade de polimerização, os diâmetros médios de partículas, o teor de monômero residual, o teor de insolúveis e o teor de resíduos foram avaliados. A cromatografia gasosa foi aplicada com sucesso em análises de látex e monômeros com finalidades diversas, destacando-se a obtenção de coeficientes de atividade necessários ao modelo de equilíbrio líquido-vapor, análise da concentração de monômeros ao longo da reação e análise da concentração de monômero residual. / In this work, studies of the styrene butadiene emulsion copolymerization had been performed in two stages. The first stage composed of a mathematical model that represented the batch and semi continuous process. In the second stage, the effects of diverse process variables were evaluated, among them: the time of addition of the reagents, feeding type and temperature reaction. The mathematical model was based on previously published work that it was adapted to simulate the styrene butadiene emulsion copolymerization process. Batch and semi continuous processes were simulated. In assembly with the experimental results, Marquardt method was applied to estimate some parameters that wasn’t found in literature. The variable process and the properties of polymer, such as, conversion, particle diameter, rate of polymerization and pressure of the reactor had been also simulated to batch and semicontinous process. A liquid-vapor balance of monomers model was proposed. The experimental stage had been carried through in a semi continuous stirring jacket tank reactor with 3 liters. Sodium persulfate as initiating, sodium lauryl sulfate as surfactant and Tert dodecyl mercaptan as chain transference agent had been used. The effect of temperature, type and time feeding had been studied. Polymerization rate, particles diameter, residual monomer had been evaluated. The gaseous chromatography was successfully applied in analyses of latex with diverse purposes: activity coefficient estimation, adjustment of liquid-vapor model, analysis of residual monomer of the reaction and volatiles organic components concentration in final latex.

O reator anaeróbio de leito fixo tem demonstrado viabilidade para produzir hidrogênio a partir de águas residuárias. No entanto, a liberação do biogás não tem sido contínua devido à diminuição constante da carga orgânica volumétrica específica (COVe) causada pelo acúmulo de biomassa no leito ao longo do tempo. A redução da COVe junto com o envelhecimento da biomassa tem sugerido o estabelecimento de microorganismos consumidores dos constituintes do biogás (H2/CO2) responsáveis por cessar a produção de hidrogênio. Neste trabalho, cinco estratégias foram propostas visando a produção de hidrogênio por longo prazo operacional e com estabilidade, mediante a fixação da COVe, as quais incluíram a alteração da estruturação do leito, inverter o escoamento, realizar descartes periódicos de biomassa e variar a carga orgânica volumétrica aplicada (COV) por meio da variação do tempo de detenção hidráulica (TDH) e da concentração do substrato. Os resultados demonstraram que a manutenção da COVe em um valor adequado permite a produção contínua de hidrogênio. A ordenação do leito, utilizando polietileno de baixa densidade e espuma, e o escoamento descendente favoreceram a diminuição do acúmulo de biomassa e junto com os descartes de biomassa foi possível manter a COVe em um valor estável próximo de 5 g sacarose g-1 SSV d-1. A produção volumétrica de hidrogênio (PVH) foi contínua com valor médio de 0,6 L H2 L-1 d-1 e rendimento (YH2) próximo a 0,5 mol H2 mol-1 sc. Por outro lado, o escoamento ascendente e os descartes de biomassa em reator de leito empacotado e ordenado atingiram uma PVH média de 2,2 ± 0,2 e 3,13 ± 0,07 L H2 L-1 d-1 quando a COVe foi mantida em 2,6 e 4,4 g sacarose g-1 SSV d-1, respectivamente. Por último a variação da COV permitiu manter a COVe entre 3,8 e 6,2 g sacarose g-1 SSV d-1, atingindo um YH2 médio de 2 mol H2 mol-1 sc e um incremento da PHV de 2,4 a 8,9 L H2 L-1 d-1 durante 60 dias consecutivos. Ainda que com resultados satisfatórios referentes à manutenção por longo período operacional e estabilidade na produção de hidrogênio, a supersaturação deste gás no meio líquido, devido a limitações de transferência de massa, foi a principal causa de perdas de hidrogênio neste tipo de reator. / Fixed-bed, anaerobic reactor has been shown to be feasible for hydrogen production from wastewater. However, biogas release has not been continuous due to the continuous specific organic load (SOL) decrease, which in turn is caused by biomass accumulation in the bed, through the time. SOL reduction and biomass ageing have indicated the establishment of the microorganisms that consumes the biogas constituents (H2/CO2) as the main cause for ceasing hydrogen production. In this work, five strategies were proposed aiming at obtaining longterm, stable hydrogen production by using SOL maintenance, modifications of the bed structure, flow inversion, periodic biomass discards and diverse organic load rates (OLR), as a function of the hydraulic retention time (HRT) and of the substrate concentration. Results demonstrated that by maintaining the SOL at proper values, continuous hydrogen production can be accomplished. On one hand, structuring the bed by using low-density polyethylene and foam, together with a down-flow and biomass discards were shown to diminish biomass accumulation, which led to keep a stable SOL value close to 5 g sucrose g-1 VSS d-1. Volumetric hydrogen production (VHP) was continuous with an average value of 0.6 L H2 L-1 d-1 and a yield (YH2) close to 0.5 mol H2 mol-1 sc. On the other hand, up-flow with biomass discharges, when implemented structured-bed and packed-bed reactors reached average VHP values of 2.2 ± 0.2 and 3.13 ± 0.07 L H2 L-1 d-1 as SOL was maintained between 2.6 and 4.4 g sucrose g-1 VSS d-1, respectively. Eventually, SOL was kept between 3.8 e 6.2 g sucrose g-1 VSS d-1 by varying the OLR, thus reaching an average YH2 value of 2 mol H2 mol-1 sc and a VHP increase from 2.4 to 8.9 L H2 L-1 d-1, along sixty consecutive days. As a consequence of mass-transfer limitations, oversaturation of hydrogen at the liquid medium was found as the main factor that causes hydrogen losses concerning fixed-bed reactors, even though the proposed strategies did indeed demonstrate long-term and stable hydrogen production.

Embora seja uma técnica tradicional, empregada largamente em processos industriais, a operação unitária de aeração pode ser otimizada ao se utilizar modelos matemáticos que descrevam seu comportamento hidrodinâmico. Diversas equações se prestam a esse fim, no entanto, avanços tecnológicos, tanto no campo instrumental como computacional, permitiram a obtenção de equações mais realísticas e abrangentes. Neste trabalho foram ajustadas e avaliadas equações para descrever três importantes parâmetros envolvidos na transferência de oxigênio em meio hídrico: coeficiente volumétrico de transferência de massa, fração de vazios e velocidade ascensional de bolhas. Para tanto, ademais da utilização de conceitos teóricos amplamente difundidos no meio acadêmico, empregou-se um conjunto de dados já existente. Essa combinação permitiu a avaliação e aproximação das equações teóricas à realidade experimental através de coeficientes de ajuste empíricos. Foram obtidos os seguintes resultados: a) revisão bibliográfica e sugestão da correlação que melhor descreve o coeficiente volumétrico de transferência de massa; b) correlação que descreve a fração de vazios, a partir da analise da concentração de bolhas segundo distribuições gaussianas; c) correlação que descreve a velocidade ascensional de bolhas em plumas. A complexidade de cada parâmetro obtido deixou clara a importância da análise isolada, precedendo a convolução dos mesmos em um único modelo, pois embora as resposta e recomendações apresentadas não forneçam conclusões definitivas sobre todos os aspectos envolvidos na transferência de oxigênio em meio hídrico, suas considerações pontuais contribuem sobremaneira ao domínio do fenômeno global, beneficiando modelagens matemáticas futuras. / Although it is a traditional technique, widely employed in industrial processes, the unit operation of aeration can be optimized when resorting to mathematical models which describe their hydrodynamic behavior. A range of equations lends itself to this purpose, however, technological advances both in the instrumental as computational field, allowed the achievement of equations more realistic and comprehensives. In this study were adjusted and evaluated equations to describe three important parameters involved in the oxygen transfer in the hydric medium: volumetric mass transfer coefficient, void fraction and upflow bubble velocity. To this end, besides the use of theoretical concepts widely disseminated in the academic literature, it was employed a set of already existing data. This combination allowed the evaluation and approximation of theoretical equations to experimental reality by means of empirical adjustment coefficients. Were obtained the following results: a) literature review and suggestion of the best correlation which describes the volumetric mass transfer coefficient, b) correlation which describes the fraction of voids, from the analysis of the concentration of bubbles by Gaussian distributions, c) correlation which describes the upflow velocity of swarms of bubbles. The complexity of each parameter obtained made clear the importance of the isolated analysis, preceding the convolution of them in a single model because although the answers and recommendations given fail to supply definitive conclusions on all aspects involved in the transfer of oxygen in hydric medium, their specific considerations contribute to the knowledge of the global phenomenon, benefiting deeply future mathematical models.

O reator anaeróbio em batelada seqüencial é constituído por um frasco de vidro cilíndrico de volume total de cinco litros, envolvido por uma camisa de vidro, por onde escoa a água aquecida, permitindo a operação em temperatura controlada. A biomassa encontra-se imobilizada em partículas cúbicas de espuma de poliuretano (densidade aparente de 23 kg/\'M POT.3\', as quais estão colocadas em um cesto adaptado dentro do frasco cilíndrico. A mistura é promovida por três impelidores de 3,0 cm de diâmetro, distanciados 4,0 cm um do outro, situados ao longo do eixo vertical no centro do reator. O desempenho dessa nova configuração de reator anaeróbio foi avaliado sob diferentes condições os efeitos de transferência de massa nas fases sólida e líquida. Todos os ensaios foram efetuados à temperatura de 30 ± 1 grau Celsius. Cada batelada compreende três etapas: alimentação, reação e descarga. Para avaliar os efeitos da transferência de massa na fase sólida foram feitos quatro ensaios utilizando-se partículas cúbicas de espumas de poliuretano com tamanhos de 0,5 cm; 1,0 cm; 2,0 cm e 3,0 cm de lado, com impelidor tipo hélice e intensidade de agitação de 500 rpm, determinada através de um ensaio preliminar. Para avaliar os efeitos da transferência de massa nas fases sólida e líquida foram feitos experimentos com quatro tipos de impelidores: hélice, turbina plana, turbina inclinada e turbina curva, com intensidades de agitação na faixa de 100 rpm a 1100 rpm. Também foram realizados ensaios hidrodinâmicos para verificar o tempo de mistura e ensaio para verificar a condição de anaerobiose no sistema. A água residuária utilizada em todos os ensaios foi sintética com concentração de 530 ± 37 mg DQO/L. Em todas as condições estudadas o reator apresentou boa eficiência de remoção da matéria orgânica, em torno de 87%. A concentração efluente de ácidos voláteis totais manteve-se em 13 ± 9 mg HAc/L, alcalinidade a bicarbonato de 223 ± 14 mg Ca\'CO IND.3\'/L e pH entre 6,7 e 7,2. A transferência de massa na fase sólida não foi a etapa limitante na conversão da matéria orgânica, quando partículas de 0,5 cm a 2,0 cm de aresta foram usadas no reator anaeróbio em batelada seqüencial. A resistência à transferência de massa na fase sólida somente influenciou a taxa global de reação, quando foram usados tamanhos de partículas cúbicas de 3,0 cm de aresta. A resistência à transferência de massa na fase líquida não foi somente afetada pela intensidade de agitação, mas também pela eficiência da mistura obtida por cada tipo de impelidor. A mistura do líquido dentro do reator obtida pelo impelidor turbina plana foi a mais eficiente. O uso deste tipo de impelidor resultou em menores consumos de energia e ótimo desempenho do reator com baixas taxas de agitação. Os resultados deste estudo permitiram concluir que esta nova configuração não permite a manutenção de condição de anaerobiose estrita no meio, principalmente quando altas intensidades de agitação foram aplicadas e as limitações da eficiência do processo, neste sistema, estão relacionadas principalmente as resistências à transferência de massa do que restrições cinéticas bioquímicas. / The bench-scale anaerobic sequencing batch reactor consisted of a cylindrical glass flask with a total capacity of 5 liters. The reactor was surrounded by a water jacket that allowed the operation to proceed at a constant temperature throughout the experiment. The biomass was immobilized in 5-mm cubic particles of polyurethane foam (apparent density of 23 kg/\'M POT.3\') placed in a basket inside the cylindrical flask. The mixing was provided by three mechanical impellers with diameters of 3 cm, placed 4 cm apart along a vertical axis, at the center of the reactor. All experiments were conducted at the temperature of 30 Celsius degrees. Each batch consisted of three steps: feed, react and liquid withdrawal. The performance of this new reactor configuration was evaluated under different conditions of solid and liquid-phase mass transfer. In order to evaluate the effects of the solid-phase mass transfer, four experiments were carried out with cubical polyurethane foam particles of 0.5 cm, 1.0 cm, 2.0, cm and 3.0 cm side, and with propeller impellers rotating at 500 rpm, achieved by preliminary experiment. The effects of the liquid-phase mass transfer were evaluated through four experiments with four types of impellers: propeller, flat-blade, pitched-blade and curved-blade turbines, at agitation rates from 100 rpm and 1100 rpm. A hydrodynamic test was also carried out in order to verify the mixing time, energy consumption and occurrence of strict anaerobic activity in system. A low-strength synthetic substrate was used in all the experiments with a mean chemical oxygen demand (COD) of 530 ± 37 mg DQO/L. The influence of the solid and liquid-phase mass transfer on the reactor\'s performance was assessed by measuring COD temporal profiles along batch cycles. In all conditions studied the reactor achieved good efficiency, with mean removal of organic matter (COD) of 87%. The effluent mean TVA concentration was 13 ± 9 mg HAc/L, bicarbonate alkalinity was 223 ± 14 mg Ca\'CO IND.3\'/L and the pH values ranged from 6,7 e 7,2. The solid-phase mass transfer was not the limiting step in the organic matter conversion when 0.5 to 2.0-cm side bioparticles were used in the anaerobic sequencing batch reactor. Solid-phase mass transfer resistance only influenced the overall reaction rate when 3.0-cm cubic bioparticles were used. The liquid-phase mass transfer resistance was affected both by agitation and by efficiency of mixture provided by each type of impeller. Among the impellers assayed, the flat-blade one was the most efficient in providing the required mixing conditions. The use of this type impeller resulted in small energy consumption and excellent performance of the reactor with low agitation rate (N = 300 rpm). The results of this study also indicated that this new configuration did not provide conditions for the establishment of strict anaerobic conditions, mainly when high agitation rates were used. Anaerobic process efficiency limitations in this system were mainly related to mass transfer resistances rather than biochemical kinetic restrictions.

La polymérisation de l'éthylène en phase gaz en présence d'un système catalytique supporté en réacteurs à lit fluidisés reste le procédé le plus utilisé pour la production de polyéthylène à basse densité linéaire. De plus, dans le cas du polyéthylène à haute densité, celui-ci représente également une part non négligeable des plants de production à travers le monde. Le procédé en phase gaz offre de nombreux avantages dont un coût d'exploitations inférieures et une flexibilité supérieure en termes de production des différents types de polymères comparé aux autres procédés conventionnels. Cependant, au regard de la nature exothermique de la réaction de polymérisation, la vitesse de la production du polymère dans ces réacteurs est limitée par la vitesse à laquelle la chaleur produite par la réaction peut être évacuée. Si le réacteur ne permet pas l'évacuation de cette chaleur, l'augmentation de la vitesse de production résulterait en une croissance dramatique de la température au sein du réacteur et, par conséquent, à la fusion et l'agglomération du polymère, et finalement à l'arrêt du réacteur. Dans ce cas, dans le but d'avoir une vitesse de production plus importante, il est possible d'utiliser le réacteur susnommé en tant que mode d'opération condensé. Dans le cas de ce mode d'opération, le flux d'alimentation de la phase gaz du réacteur contient non seulement de l'éthylène, de l'azote, de l'hydrogène, et éventuellement un comonomère, mais également un agent condensant inerte (ACI) tels que le pentane ou l'hexane. Dans cette configuration, le flux d'alimentation est en partie liquéfié dans un échangeur de chaleur externe en le refroidissant sous le point de rosée du gaz. Par vaporisation de la phase liquide dans le réacteur, une quantité plus importante de chaleur peut être retirée de l'environnement du réacteur grâce à la chaleur latente associée à la vaporisation. Cela permet d'obtenir un rendement plus élevé de l'espace pour ce réacteur et par conséquent une vitesse de production supérieure / In the current thesis study it is intended to investigate the potential effect of the inert condensing agent (ICA) of n-hexane used in condensed mode operation on the solubility of ethylene in produced polyethylene (PE) and consequently the quality and rate of gas phase ethylene polymerization on supported catalyst under reactive conditions. This is the first time for such a study. Performing the set of designed polymerization reaction experiments using a lab-scale stirred-bed gas phase reactor, it is observed that the instantaneous rate of ethylene polymerization increases in the presence of n-hexane, thus supporting the initial speculation of the effect of n-hexane on the enhancement of the ethylene solubility in polymer known as “cosolubility” phenomenon. In order to have a better picture and understanding, the averaged instantaneous rate of polymerization in presence of n-hexane is normalized with the one without any n-hexane. Consequently, this helps to see that while the effect of n-hexane increases proportionally to its partial pressure in the gas phase composition, this effect is more pronounced at the initial steps during the course of polymerization. In the current thesis study for the first time, the Sanchez-Lacombe EOS as one of the most widely applied thermodynamic models in polymer industry is adapted and developed in order to study not only the solubility but also concentration of ethylene in polyethylene in the absence and presence of an inert condensing agent in order to quantify the speculated cosorption phenomenon under the reactive polymerization condition. By incorporating this thermodynamic model to describe the solubility of ethylene in polymer into a single particle model like Polymer Flow Model (PFM) to estimate the concentration and temperature gradient through a growing polymer particle, it is ultimately attempted to predict the effect of change in the process operating condition by addition of n-hexane as the ICA to the gas phase composition. Finally in the current thesis study, it is demonstrated how the thermal effect associated with the heat of sorption of ICAs can have a positive effect in terms of avoiding particle over-heating under certain circumstances like its temporary exposition to the defluidized regions inside a fluidized reactor (FBR) as a possible undesirable operating condition for this type of reactor set-ups

La climatisation par absorption est un système de production de froid tritherme énergétiquement intéressant. La compression mécanique intervenant au sein des systèmes classiques à compression de vapeur (premier poste de consommation énergétique) est remplacée par une compression dite thermochimique nécessitant un apport de chaleur important. Dans le cas d'une application automobile il est possible de faire fonctionner le système grâce aux pertes thermiques du moteur. La climatisation par absorption est à l'étude au sein du service R&D du fabricant d'automobiles PSA Peugeot Citroën depuis une décennie. L'innovation majeure de PSA concerne l’évaporateur/absorbeur : un nouveau système basé sur le confinement du réfrigérant et de la solution absorbante à l'intérieur de structures capillaires a été breveté. Ce nouveau système a pour but d'éviter le mélange intempestif des fluides. L'analyse expérimentale de cet évaporateur/absorbeur a montré que la puissance frigorifique est limitée par le phénomène d'absorption. Il a été prouvé que l'effet frigorifique produit par le système est égal à un tiers de l'effet maximal qui pourrait théoriquement être réalisé. Un modèle simple de la zone d'absorption est proposé, il fournit une ligne directrice pour améliorer la conception du composant. Une revue de la littérature a montré que les modèles d'absorption sont basés sur des hypothèses dont la fiabilité n'est pas évidente. Aussi, la plupart des auteurs considèrent que les propriétés thermophysiques sont constantes. Cette hypothèse a été étudiée dans le cas simple de l'absorption statique. La modélisation des transferts simultanés de chaleur et de masse au sein de la solution absorbante nécessite de prendre en compte l'augmentation de volume de cette dernière. Les équations régissant les transferts ont été résolues par la méthode des volumes finis, sur un maillage dynamique. Deux procédures pour la déformation du maillage ont été mises en oeuvre et comparées. Les résultats numériques ont été comparés aux résultats expérimentaux obtenus sur un banc développé dans le cadre de ce travail et aux données expérimentales issues de la littérature. Enfin, l'impact des gaz incondensables sur le taux d'absorption a été étudié numériquement et expérimentalement, dans le cas de l'absorption statique. Cette étude a permis de confirmer les phénomènes à l'origine de la diminution du taux d'absorption. Cependant, l'effet de la gravité sur l'impact des gaz incondensables n'a pas pu être clarifié avec certitude. / Automotive air conditioning systems are based on the vapour compression cycle that requires mechanical energy for its operation. This mechanical energy is provided by the engine, which engenders year-averaged fuel extra consumptions, and thereby extra pollutant emissions, of the order of 5 %. Absorption cooling technology is of interest as this system could be driven by the engine waste heat.The absorption air conditioning technology has been under the scope of the R&D services of the french manufacturer PSA Peugeot Citroën for a decade. PSA's major innovation concerns the evaporator/absorber: a new system based on the confinement inside capillary structures of refrigerant and absorbent falling films has been patented. This new layout aims at avoiding unwanted mixing of the fluids. Experimental analysis of this original component has shown that the refrigerating effect is limited by the absorption phenomenon. It was proved that the refrigerating effect produced by the system is equal to one third of the maximal effect that could be achieved. A simple model of the absorption part has been proposed. It provides a guideline to improve the design of the component. A literature review has revealed that the absorption models are based on assumptions whose reliability is not obvious. Especially, most of the authors assume that the thermophysical properties are constant. The impact of this assumption has been clarified in the simple case of pool absorption. Modeling the simultaneous heat and mass transfer that takes place in the liquid absorbent requires to account for the increase of the liquid volume. This was achieved by means of a finite-volume treatment of the governing equations over a dynamic grid. Two procedures for the grid deformation have been implemented and compared. The numerical results have been compared to experimental results obtained on a bench developed on purpose and to experimental data from the literature. Finally, the impact of the non-absorbable gases on the absorption rate has been investigated numerically and experimentally, in the pool absorption case. This study enabled to confirm the phenomena at the origin of the decrease of the absorption rate. However, we could not clarify with certainty the importance of gravity-driven flows in the vapour phase, in the presence of non-absorbable gases.

La climatisation automobile est un enjeu majeur pour les constructeurs automobiles dans la mesure où elle occasionne un rejet de 10 g de CO2 par km, une surconsommation énergétique de près de 5 % et sera pris en compte dans le bilan MEVG à l'horizon 2020. Dans cette perspective, le constructeur automobile PSA Peugeot Citroën a développé un nouveau procédé : la climatisation par absorption de vapeur d'eau par une solution saline de bromure de lithium, qui marque la rupture avec le système classique à compression de vapeur. Le travail mené dans ce manuscrit s'est focalisé au niveau de l'organe principal du système, l'évaporateur/absorbeur où les deux fluides s'écoulent et sont confinés chacun entre deux grilles tissées par des effets capillaires. Les transferts de masse et de chaleur qui s'y produisent, ont lieu à l'interface liquide/vapeur formée par des ménisques de forme complexe qui constituent la surface de d'échange. L'objectif est d'intensifier les transferts de masse et de chaleur qui diffuse à travers l'interface. Un banc expérimental permettant la description tridimensionnelle de la forme des ménisques au moyen de la microscopie confocale a été développé. Le modèle « volume of fluid » a été utilisé pour la reconstruction numérique de l'interface liquide/ vapeur. La comparaison entre les données expérimentales et les simulations numériques a montré un bon accord. Ces simulations montrent que l'écoulement est influencé par la grille avec la création de zones mortes et des mouvements de vorticité. Une optimisation numérique a été menée avec comme fonction objectif le flux qui diffuse à travers l'interface. Celle-ci a permis de définir des paramètres optimales de la grille permettant d’atteindre un flux de chaleur de près de 2,5 fois supérieur à celui du cas de référence. Cette optimisation a permis l'identification d'une zone préférentielle dans laquelle les transferts de chaleur sont maxima. Le travail a aussi abordé l'influence de la forme des fils et de la forme des ménisques, montrant qu'il est préférable d’adopter des matériaux à caractère hydrophobe avec des fils à section circulaire. / Abstract The automotive air conditioning is a major challenge for the automotive manufacturers insofar it causes a release of 10 g/CO2/km, engenders an extrafuel consumption of 5 % and will be taken into account in the balance sheet in 2020 MEVG. In this perspective, the automotives constructor PSA Peugeot Citroën has developed a new process, absorption air conditioning of water vapor by lithium bromide solution, which marks a break with the classic vapor-compression system. This manuscript is focused at the main body of the system, an innovative evaporator/absorber where both fluids are flowing down and confined between two finely meshed plastic wire screens and maintained between them by capillary effects. The heat and mass transfers in this system occur at the liquid/vapour interface formed by complex menisci that represent the surface of transfer. An experimental test bench allowing the description of three-dimensional shape of menisci using confocal microscopy has been carried. The volume of fluid model has been used for the numerical reconstruction of the liquid/vapour interface. The comparison between numerical and experimental data has shown a good agreement. Numerical simulations have shown that the flow is influenced by the geometry that promotes the creation of stagnant layer solution and vorticity zones. A numerical optimization has been carried with as objective function the heat rate that di uses through the interface. This one has allowed to get out the optimal parameters allowing to have an heat rate of more than 2.5 times higher compared to the reference case. This optimization has highlighted a preferential zone in which heat transfers are maximum. The work has also dealt with the e ect of the shape of the wires and the effect of the shape of menisci on the transfer, showing that it is preferable to work with hydrophobic materials and with cylindrical wires.

The aim of the thesis is the development and improvement of the experimental techniques for fluid examination. The thesis consists of two parts and both examine heat and mass transfer in liquids using the optical methods and thermal analysis. The first part deals with the measurement techniques for studying flow patterns and their stability in systems with gas/liquid interface, in particular, in a liquid bridge system. The second part is aimed at the improvement of the existing experimental techniques to study the heat/mass transfer in the mixtures with Soret effect, enclosed in a container.<p><p>Part A is motivated by preparation of the experiment JEREMI (The Japanese-European Research Experiment on Marangoni Instability) to be performed on the International Space Station (ISS). One of the objectives of the experiment is the control of the threshold of an oscillatory flow in the liquid zone by the temperature and velocity of the ambient gas. The developed set-up for a liquid bridge allows to blow gas parallel to the interface at different temperatures and investigate the effects of viscous and thermal stresses on the stability of the flow. The present study reports on isothermal experiments with moving gas and non-isothermal experiments with motionless gas when the cooling of the interface occurs due to evaporation. The discussion concerning the experimental observations is based on two sources: an interface shape measured optically and the records on thermocouples giving an indication of how temperature and frequency evolve over time.<p><p>Part B is related to ground-based studies in course of preparation and realization of the microgravity experiment DCMIX (Diffusion Coefficient in MIXtures). DCMIX project is a series of experiments aimed at measuring of the Soret coefficients in liquid mixtures on the ISS which involves a wide international group of scientists. Two experiments have been recently completed and the third one is under preparation In the course of this thesis all the aspects of the previously existing set-up for measurements of the Soret (thermal diffusion) and diffusion coefficients in binary mixtures were studied, uncertainties were identified and improvements were done to obtain reliable results. The final design has been validated by measuring coefficients in three binary benchmark mixtures and water-isopropanol. The obtained results agree well with literature data. / Doctorat en Sciences de l'ingénieur / info:eu-repo/semantics/nonPublished