O fenômeno da transferência de massa entre dois meios é altamente dependente da concentração do componente a ser transferido e da velocidade na camada limite de troca. A medida de velocidade na superfície da água em uma interface ar/água ainda não é realidade devido a falta de instrumental adequado. Procurando sanar este obstáculo, esta pesquisa propôs o desenvolvimento de uma sonda ótica para medida de turbulência na superfície da água em um tanque agitado por grade oscilante. O funcionamento desta sonda foi investigado e suas medidas comparadas a medidas realizadas pelo instrumento microADV, de forma a verificar se o parâmetro medido pelo novo instrumento era relacionado à componente vertical da velocidade próximo à superfície. O comportamento do escoamento no tanque foi modelado com o uso do software Open-FOAM, visando uma maior compreensão do fenômeno. A pesquisa resultou na modelação do escoamento e no desenvolvimento de um dispositivo auxiliar que possibilita o uso do microADV em medidas próximas à superfície livre. A comparação das medidas adquiridas pela sonda ótica e microADV mostram que, apesar de as medidas da sonda terem relação com a turbulência no tanque, este parâmetro turbulento apresenta fraca correlação com a medida da componente vertical da velocidade. / The mass transfer phenomena is highly dependent on the concentration of the component to be transferred and the velocity on the exchange layer. The velocity measurement at the surface of the water in an air / water interface is not yet a reality due to lack of appropriate instruments. In order to overcome this obstacle, this research proposed the development of an optical probe to measure turbulence on the surface of water in an oscillating grid tank. We investigated the operation of the proposed probe comparing its measurements to measurements made by microADV to check the relation between the parameter measured by the new instrument and the vertical velocity near to the surface. The flow behavior in the tank was MODELLED using the software OpenFOAM seeking a greater understanding of the phenomenon. The research resulted in the modeling of the flow in the tank and the development of an auxiliary device that allows the use of microADV in near-surface measurements. Although the probe measurement have relation with the turbulence in the tank, the comparison of measurements acquired by the optical probe and microADV shows the turbulent parameter presenting weak correlation to the measurement of the vertical velocity.

Nesta dissertação de mestrado é estudado o desempenho fluidodinâmico de um meio poroso fixo e compactado, construído por sinterização com esferas de vidro para a retenção de partículas. A análise experimental visou o processo de retenção de partículas a partir de pastilhas circulares de diâmetro de 29 mm confeccionadas com esferas de vidro variando de 1,0 a 3,3 mm de diâmetro e sinterizadas como um elemento rígido a partir de aquecimento contínuo até cerca de 750ºC. As pastilhas foram submetidas a diferentes pressões de coluna de água, e a vazão no meio poroso foi analisada para diferentes pressões. Os experimentos foram realizados com a adição em batelada de polpa de açaí, areia fina, areia grossa e esferas de vidro próprias da composição do meio poroso. As vazões mássicas adimensionais são apresentadas graficamente para diferentes pressões de coluna de água variando entre 0,1 e 0,5 atmosferas (atm), em regime permanente e estacionário. Os resultados experimentais foram comparados e apresentados na forma de parâmetros adimensionais que caracterizam o regime de escoamento num leito fixo. Os resultados experimentais foram modelados a partir da modificação dos modelos de Vortmeyer e Schuster (1983) e Subagyo et al. (1998) para estabelecer sobre os mesmos parâmetros adimensionais uma adequada aproximação com os resultados teóricos. / The present dissertation reports the performance of steady flow in circular fix bed which was created by sinterization of glass spheres. The experimental analysis aimed the process of retention of particles from circular packed bed of 29 mm of diameter. The circular fix bed was created with spheres of glass of diameter between 1.0 and 3.0 mm, and made by sintering one rigid body from continuous heating until 750ºC. The circular and rigid fix bed was subjected to different pressures of column of water varying between 0.1 and 0.5 atm for analysis of flux (kg/s). The experiments were carried out with the addition of one amount of açai pulp, sands fine, sands thick and spheres of glass own of composition of fix bed. The dimensionless flux was present for different pressures of column of water on the fix bed; the results were compared and presented in the form of dimensionless parameters of literature what characterize the flow in packed bed. The experimental results were modeled based on Vortmeyer e Schuster (1983) and Subagyo et al. (1998) models, establishing on the dimensionless parameters an appropriate approach with the theoretical flux of circular fix bed.

Conventional heat transfer enhancement methods have focused on the surface characteristics of the heat-exchanger. The enhancement of heat transfer through altering the characteristics of the working fluid has become a new subject of interest. Micro-encapsulated phase change material (MEPCM) slurries show improved heat transfer abilities compared to single phase heat transfer fluids such as water due to their higher specific heat values in their phase change temperature range. The present work is a numerical and experimental study towards fundamental understanding of the impact of using PCM on thermal and fluid flow characteristics of different single-phase and two-phase heat transfer applications. The mathematical formulation to represent the presence of single and multi-component MEPCM is developed and incorporated into the numerical model for single-phase and two-phase fluid flow systems. In particular, the use of PCM in its encapsulated form for heat transfer enhancement of liquid flow in the presence of evaporation is explored. In addition, an experimental study is conducted to validate the numerical model in a setting of natural convection flow. Finally, the application of PCM in its layered form on the effectiveness of drying of moist porous materials (e.g. paper) is investigated.

"Gas carburizing is an important heat treatment process used for steel surface hardening of automotive and aerospace components. The quality of the carburized parts is determined by the hardness and the case depth required for a particular application. Despite its worldwide application, the current carburizing process performance faces some challenges in process control and variability. Case depth variability if often encountered in the carburized parts and may present problems with i) manufacturing quality rejections when tight tolerances are imposed or ii) insufficient mechanical properties and increased failure rate in service. The industrial approach to these problems often involves trial and error methods and empirical analysis, both of which are expensive, time consuming and, most importantly, rarely yield optimal solutions. The objective for this work was to develop a fundamental understanding of the mass transfer during gas carburizing process and to develop a strategy for the process control and optimization. The research methodology was based on both experimental work and theoretical developments, and included modeling the thermodynamics of the carburizing atmosphere with various enriching gasses, kinetics of mass transfer at the gas-steel interface and carbon diffusion in steel. The models accurately predict: 1) the atmosphere gas composition during the enriching stage of carburizing, 2) the kinetics of carbon transfer at the gas-steel surfaces, and 3) the carbon diffusion coefficient in steel for various process conditions and steel alloying. The above models and investigations were further combined to accurately predict the surface carbon concentration and the carbon concentration profile in the steel during the heat treatment process. Finally, these models were used to develop a methodology for the process optimization to minimize case depth variation, carburizing cycle time and total cycle cost. Application of this optimization technique provides a tradeoff between minimizing the case depth variation and total cycle cost and results in significant energy reduction by shortening cycle time and thereby enhancing carburizing furnace capacity."

Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 1979. / MICROFICHE COPY AVAILABLE IN ARCHIVES AND SCIENCE. / Includes bibliographical references. / M.S.

<div>Liquid desiccant air dehumidification (LDAD) is a promising substitute for the conventional dehumidification systems that use mechanical cooling. However, the LDAD system shares a little market because of its high installation cost, carryover problem, and severe corrosion problem caused by the conventional liquid desiccant. The research reported in this thesis aimed to address these challenges by applying membrane technology and ionic liquid desiccants (ILDs) in LDAD. The membrane technology uses semi-permeable materials to separate the air and liquid desiccants, therefore, the solution droplets cannot enter into the air stream to corrode the metal piping and degrade the air quality. The ILDs are synthesized salts in the liquid phase, with a large dehumidification capacity but no corrosion problems. In order to study the applicability and performance of these two technologies, both experimental and modeling investigations were made as follows.</div><div>In the study, experimental researches and existing models on the membrane-based LDAD (MLDAD) was extensively reviewed with respects of the characteristics of liquid desiccants and membranes, the module design, the performance assessment and comparison, as well as the modeling methods for MLDAD.</div><div>A small-scale prototype of the MLDAD was tested by using ILD in controlled conditions to characterize its performance in Oak Ridge National Lab. The preliminary experimental results indicated that the MLDAD was able to dehumidify the air and the ILD could be regenerated at 40 ºC temperature. However, the latent effectiveness is relatively lower compared with conventional LDAD systems, and the current design was prone to leakage, especially under the conditions of high air and solution flow rates.</div><div>To improve the dehumidification performance of our MLDAD prototype, the two-dimensional numerical heat and mass transfer models were developed for both porous and nonporous membranes based on the microstructure of the membrane material. The finite element method was used to solve the equations in MATLAB. The models for porous and nonporous membranes were validated by the experimental data available from literature and our performance test, respectively. The validated models were able to predict the performance of the MLDAD module and conduct parametric studies to identify the optimal material selection, design, and operation of the MLDAD.</div><div><br></div>

The major concern of this work is the development of hierarchically porous structured zeolite composites for ion-exchange applications by deposition of a thin layer of zeolite on inexpensive porous supports which offers better efficiency in separation processes. The merits of utilization of zeolite composites in industrial applications are generally reducing mass transfer resistance and pressure drop. In addition to this they have advantages in the removal of metal ions from wastewater such as increasing the metals uptake and minimizing the volume of waste disposed especially after vitrification. This thesis presents results from a combination of experimental work and simulation study of experimental data to give isotherm and kinetic models. The experimental work shed light on the preparation of zeolite composites using zeolite X (Si/Al ~ 1.35) and clinoptilolite (Si/Al ~ 4.3), studying the performance of these composites on the removal of the Sr2+ and Mn2+ ions and then stabilization of waste materials resulting from the ion-exchange process. Clinoptilolite was hydrothermally synthesized to show the effect of non-framework cations on the removal process. The porous supports were diatomite which is naturally occurring silica and carbon which is obtained from Iraqi date stones by a thermal treatment conducted at 900°C. Coating the support surface with zeolites crystals was conducted in two different ways. The layer by layer approach, which has not previously been used, was used to prepare monolithic carbon clinoptilolite composite using a combination of sucrose/citric acid and zeolite. The other approach was modifying the support surface by ultrasonication in the presence of nanoparticles suspension prepared using ball mill to create nucleation sites and enhance the crystal attachment during hydrothermal treatment. Characterisation was implemented in each case using XRD, SEM, EDAX, TGA and BET method. Ion-exchange experimental results showed higher ion-exchange capacity obtained when the composites were used in comparison to pure zeolites, when a comparison is based on actual weight of zeolite used for removal of Sr2+ and Mn2+ ions. A study of encapsulation of ions showed that it is feasible to solidify the waste materials by vitrification and/or geopolymerization to eliminate leaching of ions to the environment. The simulation studies showed that the ion-exchange kinetic followed the pseudo second order kinetic model. This fitting indicates that the rate of ion-exchange process is controlled by a chemical reaction related to valence forces. The overall ion-exchange process is controlled by a combination of ion-exchange reaction, film diffusion and intra-particle diffusion. Moreover, the thermodynamic studies which were conducted under different temperatures revealed that the ion-exchange of Sr2+ and Mn2+ ions is practicable, spontaneous and endothermic.

L’objectif de ce travail de thèse est la formalisation des relations entre la structure et les propriétés de transfert de matière (sorption, diffusion, perméabilité) dans des matériaux biocomposites pour l’emballage alimentaire. Pour cela, la thèse se focalise sur deux questions scientifiques majeures : (i) comment évaluer les propriétés de transfert de vapeur d’eau et de gaz dans des particules végétales de taille micrométrique et (ii) comment formaliser l’influence de l’interphase sur les propriétés de transfert de matière en utilisant des approches expérimentales et de modélisation. Pour cela, a système composite modèle a été utilisé : un biocomposite polypropylène (PP) / particules de cellulose micrométrique produit par extrusion. La première partie de ces travaux est axée sur le développement d’une méthodologie fiable pour caractériser les propriétés de transfert dans des particules de taille micrométrique. Une nouvelle méthode ad hoc couplant microbalance à quartz et cellule d’absorption a été développée et comparée aux méthodes gravimétriques classiques telles que la DVS. La caractérisation fine de la taille / distribution en taille des particules est une étape essentielle pour garantir la fiabilité de l’estimation des paramètres de diffusion. Le deuxième objectif s’appuie sur une caractérisation quantitative fine de la structure 3D des matériaux composites (micro-tomographie X). En finalité, ces travaux de thèse permettent d’aller plus loin dans le développement de modèles prédictifs des relations entre structure et propriétés de transfert de matière, ce qui est l’étape nécessaire pour développer des matériaux biocomposites basés sur une approche d’ingénierie inverse. / The objective of this thesis is to formalize the relationships between the structure and mass transfer properties (sorption, diffusion, permeability) in biocomposites for food packaging. It raises two main scientific questions: (i) how to evaluate the mass transfer properties in micrometric size vegetal particles and (ii) how to formalize the impact of the interphase on mass transfer properties by using experimental and modeling approaches. For this purpose, a model system has been considered, i.e. a biocomposite polypropylene (PP)/ micrometric cellulose particles, produced by melt extrusion. The first part of this work focuses on the development of reliable methodologies to characterize mass transfer properties in micrometer size particles. A new method based on the use of a quartz crystal microbalance coupled to an absorption system has been developed and critically compared to classical methods such as DVS. The accurate characterization of the particle morphology distribution is a key point for estimating diffusivity parameters. The second objective is dedicated to the quantitative characterization of the 3D microstructure using X-ray micro-tomography. Structural parameters are used in biphasic and triphasic (consideration of the interphase) models of mass transfer. This thesis brings new knowledge in the modeling of structure / mass transfer properties relations in biocomposites, which is the necessary step for developing biocomposites based on a reverse engineering approach.

O foco deste trabalho é o desenvolvimento de um modelo físico representativo de um absorvedor de filme líquido descendente para um ciclo de refrigeração por absorção amônia-água, considerando uma capacidade de refrigeração de 5TR. O absorvedor é constituído basicamente de feixes de tubos dispostos horizontalmente, no interior dos quais escoa água com a finalidade de retirar o calor liberado ao longo do processo de absorção. Desenvolveu-se o modelo com base na obtenção e resolução dos balanços de energia e de massa. Isso com o auxílio de correlações e analogias que possibilitaram a obtenção dos coeficientes de transferência de calor e massa. Levou-se em conta a variação das propriedades tanto do líquido como do vapor ao longo do absorvedor, assim como a resistência existente nessas duas fases. Obtiveram-se os perfis de frações e vazões mássicas, temperatura, coeficientes de transferência e taxas de transferência de amônia. Avaliou-se a influência de parâmetros importantes em se tratando de absorvedores de filme líquido descendente, tais como número de Reynolds, temperatura do fluido de resfriamento e temperatura de entrada da solução. Estes perfis possibilitaram a análise de alguns aspectos relevantes no que diz respeito ao projeto do absorvedor, considerando-se algumas condições operacionais e geométricas previamente estabelecidas. Por fim, foi possível, através da obtenção do comprimento do equipamento para as diversas condições de simulação adotadas, calcular a área de troca de calor necessária para o processo absortivo. / The goal of this work is to develop a representative physical modeling of a falling film absorber for an ammonia-water absorption refrigeration cycle, rated at cooling 5 TR. The absorber is composed of a bundle of tubes arranged horizontally. The water flows inside these tubes in order to remove the heat released during the absorption process. The model was developed based on solving the conservation equations of energy and mass. Practical correlations and the heat and mass transfer analogy were used to find the convective coefficients. It was considered the changes of the properties of liquid and vapor along the absorber and also it was taken into account the thermal resistances in each phase. It was found the profiles of mass fractions and mass flow rates, temperature, transfer coefficients and transfer rates of ammonia. It was evaluated the influence of important parameters such as the Reynolds number, cooling temperature and inlet temperature of the solution. These profiles allowed the analysis of some relevant aspects regarding the design of the absorber, considering operational and dimensional conditions preestablished. Finally, it was possible to calculate the area and other geometrical aspects to achieve the absorptive process, by analyzing the operation of the equipment at various conditions.

O processo de absorção do CO2 em soluções aquosas de alcanolaminas foi estudado em uma coluna de parede molhada empregando-se uma tela metálica, de 28 mesh, como promotor de película e operando em contracorrente. As alcanolaminas testadas nos diferentes experimentos foram: monoetanolamina (MEA), 2-amino-2-metil-1-propanol (AMP) e piperazina (PZ). Os experimentos de absorção foram realizados nas soluções aquosas individuais da MEA e AMP; e, nas misturas MEA:AMP e AMP:PZ; visando avaliar a velocidade de absorção do CO2 em diferentes vazões do líquido, a saber: 3.10-7, 6.10-7 e 10.10-7 m3/s. O presente sistema de absorção foi caracterizado através da determinação dos principais parâmetros de transferência de massa: área interfacial efetiva, coeficiente de transferência individual da fase gasosa e o coeficiente volumétrico global médio de transferência de massa. Determinou-se a área interfacial efetiva da coluna, por meio da absorção do CO2 diluído em ar em uma solução aquosa de NaOH, para as diferentes vazões de líquido, sendo os resultados obtidos igual a 106, 126 e 144 m2/m3, respectivamente. O coeficiente volumétrico de transferência de massa da fase gasosa foi determinado por meio da absorção de SO2 diluído em ar em uma solução aquosa de NaOH. Os resultados experimentais mostram que o coeficiente volumétrico individual de transferência de massa e a área interfacial são função da vazão do líquido. As velocidades de absorção do CO2 diluído em ar, em soluções de aminas e suas misturas foram determinadas experimentalmente para diferentes vazões de líquido, sendo os resultados expressos na forma de coeficientes globais de transferência de massa e parâmetros cinético-difusivos da fase líquida. As velocidades de absorção em MEA são bem superiores aos de AMP e NaOH. No caso das misturas foram obtidas velocidades superiores em comparação às das aminas individuais. A velocidade de absorção em AMP é fortemente incrementada na presença de PZ, mesmo em baixa concentração. / The CO2 absorption process in alkanolamine aqueous solutions was studied in a wetted wall column employing a film promotor of thin stainless steel woven wire, 28 mesh, which was operated in countercurrent. The tested alkanolamines were monoethanolamine (MEA), 2-amino-2-methyl-1-propanol (AMP) and piperazine (PZ). The absorption experiments were performed in individual aqueous solutions of MEA and AMP and the mixtures MEA:AMP and AMP:PZ, with the aim of evaluating the CO2 absorption rate in different liquid flow rates, namely: 3.10-7, 6.10-7 e 10.10-7 m3/s. This absorption system was characterized through determining of the main parameters of mass transfer: effective interfacial area, individual mass transfer coefficient of the gas phase and the average overall mass transfer volumetric coefficient. The effective interfacial area was determined by the absorption of CO2 diluted in air into an aqueous solution of NaOH for the different liquid flow rates, and the results obtained are 106, 126 and 144 m2/m3, respectively. The mass transfer volumetric coefficient of the gas phase was determined by chemical method of the absorption of SO2 diluted in air into an aqueous solution of NaOH. The experimental results show that the individual mass transfer coefficient and interfacial area are a function of liquid flow rate. On the other hand, the results of the performance of CO2 absorption into amine aqueous solutions were expressed in function of the average overall mass transfer volumetric coefficient and liquid phase diffusive kinetic parameters, which were measured experimentally for different liquid flow rates. The absorption rate in MEA are higher in comparison with AMP and NaOH. In the case of the blended, the absorption rate in AMP is enhanced by piperazine, even in low concentration.