Dans un procédé de séchage, l'évacuation de l'eau induit des modifications structurelles et physicochimiques qui engendrent des difficultés d'écoulement dans le séchoir. Cette étude a porté sur la modélisation du séchage continu par contact avec agitation. Nous avons développé un modèle markovien pour décrire les transferts de masse, de chaleur et l'écoulement dans un séchoir continu. Les paramètres d'entrée du modèle ont été déterminés expérimentalement sur un produit pâteux, tandis que d'autres paramètres ont été obtenus à partir de la littérature scientifique. L'étude de sensibilité de la teneur en eau et de la masse sèche retenue dans le séchoir a permis d'analyser et de hiérarchiser les effets des différentes variables opératoires. Enfin, nous avons étudié l'influence des variables opératoires sur le profil de teneur en eau, le temps de passage et les courbes de distribution de temps de séjours simulées. L'évolution structurelle du produit a été mise en évidence dans le modèle. / In a drying process, the evacuation of water induced structural and physico-chemical modifications that generate difficulties of flow in the dryer. This study focused on the modeling of agitated indirect continuous dryer. We developed a Markov model to describe the mass transfer, heat transfer and flow in a continuous dryer. The input parameters of the model were determined experimentally on a pasty product, while other parameters were obtained from the scientific literature. The sensitivity study of the moisture content and dry mass retained in the dryer was used to analyze and treat on a hierarchical basis the effects of different operating variables. Finally, we studied the influence of variables operating on the profile of moisture content, the passage time and the simulated curves of residence time distribution. The structural evolution of the product was considered in the model

The convective drying of thin layers of multicomponentliquid mixtures into an inert gas, and the influence ofdifferent process controlling mechanisms on drying selectivityis studied. Drying experiments under gas-phase-controlledconditions are performed by low intensity evaporation, fromfree liquid surfaces, of ternary mixtures without non-volatilesolutes. Liquid-side-controlled experiments are carried out bydrying a multicomponent polymeric solution containing twovolatile components, one non-volatile polymer and an optionalnonvolatile softening substance. Mathematical models to describe gas- andliquid-side-controlled drying based on interactive diffusion inboth liquid and gas phases as the main mechanisms for masstransfer are developed. For gas-phase-controlled drying, astability analysis of the ordinary differential equations thatdescribes the evaporation process is performed. Isothermal andnon-isothermal drying processes are considered in batch andcontinuous modes. The mathematical model to describe thecomposition profiles during batch drying of the polymeric film,considering liquid resistance, is solved numerically. Due tothe lack of experimental data, properties for this polymericsystem are estimated by using established methods. Ananalytical solution of the diffusion equation, by assuming anisothermal drying process and a constant matrix ofmulticomponent diffusion coefficients is developed. For thecontinuous case, liquid-side resistance is studied by modellingevaporation of a multicomponent falling liquid film into aninert gas including indirect heating. The results of the gas-phase-controlled model are in goodagreement with experimental results. For the polymeric film,the agreement is only qualitative since the model does notaccount for a membrane that develops on the film surface. Thestability analysis permits the prediction of trajectories andfinal state of a liquid mixture in a gas-phase-controlleddrying process. For isothermal evaporation of ternary mixturesinto pure gas, the solutions are trajectories in the phaseplane represented by a triangular diagram of compositions. Thepredicted ternary dynamic azeotropic points are unstable orsaddle. On the other hand, binary azeotropes are stable whenthe combination of the selectivities of the correspondingcomponents is negative. In addition, pure component singularpoints are stable when they are contained within theirrespective isolated negative selectivity zones. Undernon-isothermal conditions, maximum temperature valuescharacterise stable azeotropes. Incremental loading of the gaswith one or more of the components leads to a node-saddlebifurcation, where a saddle azeotrope and a stable azeotropecoalesce and disappear. For continuous drying, the singularpoints are infinite and represent dynamic equilibrium pointswhose stability is mainly dependent on the ratio of inletgas-to-liquid flow rates. As long as the process isgas-phasecontrolled, these results also apply to a porous solidcontaining a liquid mixture. In general, liquid-side control makes the drying processless selective but it is difficult to maintain this conditionduring the whole process. Under the influence of its owndynamics, a process starting as liquid-side-controlled tendstowards a gas-phase-controlled process. The presence ofnon-volatile components and indirect heating may delay thisdevelopment. Considering the evolution of the processcontrolling steps and its influence on selectivity, a modelaimed at describing the complete trajectory of a drying orevaporation process must include the coexistence of allrelevant mechanisms. Keywords:ternary mixture, falling film, diffusionequation, gas-phase control, liquid-phase control, selectivity,stability analysis, polymeric solution, evaporation, azeotrope,batch drying, continuous drying.

<p>The convective drying of thin layers of multicomponentliquid mixtures into an inert gas, and the influence ofdifferent process controlling mechanisms on drying selectivityis studied. Drying experiments under gas-phase-controlledconditions are performed by low intensity evaporation, fromfree liquid surfaces, of ternary mixtures without non-volatilesolutes. Liquid-side-controlled experiments are carried out bydrying a multicomponent polymeric solution containing twovolatile components, one non-volatile polymer and an optionalnonvolatile softening substance.</p><p>Mathematical models to describe gas- andliquid-side-controlled drying based on interactive diffusion inboth liquid and gas phases as the main mechanisms for masstransfer are developed. For gas-phase-controlled drying, astability analysis of the ordinary differential equations thatdescribes the evaporation process is performed. Isothermal andnon-isothermal drying processes are considered in batch andcontinuous modes. The mathematical model to describe thecomposition profiles during batch drying of the polymeric film,considering liquid resistance, is solved numerically. Due tothe lack of experimental data, properties for this polymericsystem are estimated by using established methods. Ananalytical solution of the diffusion equation, by assuming anisothermal drying process and a constant matrix ofmulticomponent diffusion coefficients is developed. For thecontinuous case, liquid-side resistance is studied by modellingevaporation of a multicomponent falling liquid film into aninert gas including indirect heating.</p><p>The results of the gas-phase-controlled model are in goodagreement with experimental results. For the polymeric film,the agreement is only qualitative since the model does notaccount for a membrane that develops on the film surface. Thestability analysis permits the prediction of trajectories andfinal state of a liquid mixture in a gas-phase-controlleddrying process. For isothermal evaporation of ternary mixturesinto pure gas, the solutions are trajectories in the phaseplane represented by a triangular diagram of compositions. Thepredicted ternary dynamic azeotropic points are unstable orsaddle. On the other hand, binary azeotropes are stable whenthe combination of the selectivities of the correspondingcomponents is negative. In addition, pure component singularpoints are stable when they are contained within theirrespective isolated negative selectivity zones. Undernon-isothermal conditions, maximum temperature valuescharacterise stable azeotropes. Incremental loading of the gaswith one or more of the components leads to a node-saddlebifurcation, where a saddle azeotrope and a stable azeotropecoalesce and disappear. For continuous drying, the singularpoints are infinite and represent dynamic equilibrium pointswhose stability is mainly dependent on the ratio of inletgas-to-liquid flow rates. As long as the process isgas-phasecontrolled, these results also apply to a porous solidcontaining a liquid mixture.</p><p>In general, liquid-side control makes the drying processless selective but it is difficult to maintain this conditionduring the whole process. Under the influence of its owndynamics, a process starting as liquid-side-controlled tendstowards a gas-phase-controlled process. The presence ofnon-volatile components and indirect heating may delay thisdevelopment. Considering the evolution of the processcontrolling steps and its influence on selectivity, a modelaimed at describing the complete trajectory of a drying orevaporation process must include the coexistence of allrelevant mechanisms.</p><p><b>Keywords:</b>ternary mixture, falling film, diffusionequation, gas-phase control, liquid-phase control, selectivity,stability analysis, polymeric solution, evaporation, azeotrope,batch drying, continuous drying.</p>

Submitted by Emanuel Varela Cardoso (emanuel.varela@ufcg.edu.br) on 2018-08-21T20:37:01Z No. of bitstreams: 1 ISRAEL BURITI GALVÃO – DISSERTAÇÃO (PPGEP) 2017.pdf: 6049302 bytes, checksum: ac315d43e0d0a7dbefdb3e01f65ae674 (MD5) / Made available in DSpace on 2018-08-21T20:37:01Z (GMT). No. of bitstreams: 1 ISRAEL BURITI GALVÃO – DISSERTAÇÃO (PPGEP) 2017.pdf: 6049302 bytes, checksum: ac315d43e0d0a7dbefdb3e01f65ae674 (MD5) Previous issue date: 2017-10-20 / O presente trabalho teve como objetivo realizar um estudo da secagem cont ínua e intermitente de pedaços de maçã fresca e pré-tratada osmoticamente, cortados na forma de paralelepípedo, utilizando modelos empíricos e difusivos na descrição da cinética desses processos. Para o modelo de difusão, foram pressupostos parâmetros termosfísicos e dimensões variáveis. Foi realizada uma revisão bibliográfica sobre o tema, detalhamento dos materiais e métodos utilizados, a validação e testes do solver em FORTRAN tridimensional desenvolvido através do método dos volumes finitos, com uma formulação totalmente implícita. Foram feitos experimentos utilizando uma incubadora refrigerada com agitação para a realização da desidratação osmótica a fim de preparar as amostras para as secagens subseqüentes. As secagens foram realizadas em uma estufa com circulação de ar nas temperaturas de 50 e 70 °C, para secagens contínuas e intermitentes das maçãs (com razão de intermitência de 2/3 e períodos de têmpera de 30 min; 60 min; e 120 min com os frutos frescos, e têmperas de 20 min e 30 min para os frutos pré-tratados osmoticamente). Os resultados das cinéticas das secagens, estimativas de parâmetros relativos às frutas estudadas, mostraram-se compatíveis com a literatura. A temperaturas e os perí odos de têmpera utilizados influenciaram significativamente as cinéticas de teor de umidade, assim como os valores dos parâmetros de processo, determinados por otimização para todas as configurações experimentadas. Este trabalho também trata sobre o impacto da secagem intermitente sobre a economia de energia. / The present work had as objective to make a study of the continuous and intermittent drying of fresh and osmotically pre-treated of apple pieces cut in form of parallelepiped, using both empirical and diffusive models to description of the kinetics of the processes. For the diffusion model, thermo-physical parameters and variable dimensions were assumed. A bibliographic review was done on the subject, details of the materials and methods used, the validation and testing of the in three-dimensional FORTRAN solver developed using the finite volume method, with a fully implicit formulation. Experiments were done using a freezer shaker incubator for the osmotic dehydration in order to prepare the samples for subsequent drying. The drying was realized in an oven with air circulation at temperatures of 50 and 70 ° C, for continuous and intermittent drying of the apples (with intermittent ratio of 2/3 and tempering periods of 30 min, 60 min and 120 min for the fresh fruits, and tempers of 20 min and 30 min for osmotically pretreated fruits). The results of drying kinetics, estimates of parameters related to the fruits studied, were compatible with the literature. At the temperatures and the tempering periods used, they significantly influenced the kinetics of the moisture content, as well as the values of the process parameters determined by optimization for all configurations. Here also is shown the impact of intermittent drying on the energy saving and how the intermittent drying change for the better the product quallity is shown.

Les voies sèches de valorisation du bois énergie sont de plus en plus exigeantes vis-à-vis de la qualité de la matière première et notamment quant à sa teneur en eau. Ainsi, une étape intermédiaire de préconditionnement, sur site industriel, tend à se développer. La mise en œuvre de séchoirs en continu est alors séduisante de par son faible coût et sa parfaite intégration dans la ligne de production. Cependant, elle n'est pas sans écueil : la variabilité de la biomasse et l'hétérogénéité des conditions climatiques au sein du séchoir rendent fastidieux le dimensionnement du séchoir et de la source de chaleur associée d'une part et la maximisation du flux matière d'autre part.Notre étude a pour ambition de développer un outil informatique d'aide à la conception et à l'optimisation de séchoirs en continu traversés par un lit condensé de particules de bois. Pour y parvenir, nous associons une approche expérimentale et une approche numérique du procédé. La démarche scientifique s'articule autour de deux échelles représentatives :- A l'échelle de la particule de bois, le modèle de Van Meel, reposant sur le concept de courbe caractéristique de séchage, est étendu : le couplage entre transferts de chaleur et de masse est rendu explicite. Nous disposons dès lors d'un modèle réactif et prédictif en conditions climatiques variables. Parallèlement, un premier dispositif expérimental original est conçu et construit pour l'étude du séchage de particules de bois isolées. Les données recueillies sont alors analysées en vue d'alimenter en paramètres et de valider le modèle semi-analytique ;- A l'échelle du séchoir, une modélisation double-échelle est adoptée pour tenir compte de l'évolution des conditions climatiques. Un soin particulier est apporté à la modélisation, se voulant être la plus proche possible des installations existantes : à ce titre, les transferts au niveau de la paroi du séchoir sont pris en compte, ainsi que la variabilité des particules de bois. Parallèlement, un second dispositif expérimental original est conçu et construit pour l'étude du séchage de particules disposées en lit. Les données recueillies sont alors confrontées aux simulations du modèle double-échelle.La validation du modèle s'étant révélée probante tant à l'échelle de la particule qu'à celle du séchoir, une utilisation du code pour l'aide à la conception et à l'optimisation d'installations industrielles a pu être envisagée. Ainsi, ce travail s'achève-t-il par deux études de cas à travers lesquelles nous explorons le potentiel du modèle pour maximiser le flux matière tout en garantissant la qualité du produit et l'efficacité énergétique du séchoir. / The dry conversion routes of wood to energy require more and more improvement in the quality of raw material, particularly regarding to its moisture content. That is why a preliminary step of preconditioning tends to be developed on the industrial sites. The use of continuous dryers is then tempting because of their low cost and their perfect integration in the production line. However it is not without pitfall: the climatic conditions heterogeneity inside the dryer, on the one hand, and the biomass variability, on the other hand, make the utilization of these industrial plants tedious.Our study aims to develop a computing tool to help engineers optimizing and to designing continuous dryers passed through by a condensed bed of wood particles. For this result, an experimental approach of the process is associated to a numerical one. The scientific method revolves around two representative scales:• At the wood particle scale, the Van Meel model, based on the concept of characteristic drying curve, is enhanced: the coupling between heat and mass transfer is made explicit. So we obtain a reactive model which is predictive when the climatic conditions are variable. Meanwhile, a first original experimental device is designed and built in order to study the drying of single wood particles. Thanks to the collected data, the semi-analytical model is provided with parameters and is validated;• At the dryer scale, a dual-scale approach is chosen in order to take into account the evolution of the climatic conditions. A particular attention is paid to the modeling in order to make it as similar as possible to the existing installations: as such, the transfers at the wall surface and the variability of wood particles are included. Meanwhile, a second original experimental device is designed and built in order to study the drying of a wood particles stack. The data collected are then confronted with simulations of the double-scale model.The validation of the model has proven to be convincing at the particle scale and at the dryer one. Therefore a utilization of the code to help in the design and optimization of industrial plants can be considered. Thus, the work ends by two case studies through which we explore the potential of the model to maximize material flow while ensuring product quality and efficiency of the dryer.