Orientadores: Theo Guenter Kieckbusch, Mariana Altenhofen da Silva / Dissertação (mestrado) - Universidade Estadual de Campínas, Faculdade de Engenharia Química / Made available in DSpace on 2018-08-21T16:22:52Z (GMT). No. of bitstreams: 1 Vaz_JulianaMiguel_M.pdf: 25278318 bytes, checksum: 2af6f4b99f503d19043c081e804f17b7 (MD5) Previous issue date: 2012 / Resumo: Alginatos são polissacarídeos compostos pela co-polimerização de unidades de beta-D-manuronato (M) e alfa-L-guluronato (G), arranjados em bloco homopoliméricos (poli-M ou poli-G) ou blocos em sequencia alternada, capazes de formar filmes resistentes quando reticulados com cálcio. ...Observação: O resumo, na íntegra, poderá ser visualizado no texto completo da tese digital / Abstract: Alginates are linear copolymers of (1,4)-linked beta-D-mannuronate (M) and alfa-L-guluronate (G) units, arranged as homopolymeric blocks (poly-M and poly-G) and blocks with alternating sequence....Note: The complete abstract is available with the full electronic document / Mestrado / Engenharia de Processos / Mestra em Engenharia Química

Orientador: Miriam Dupas Hubinger / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia de Alimentos / Made available in DSpace on 2018-08-04T02:50:30Z (GMT). No. of bitstreams: 1 Ferrari_CristhianeCaroline_M.pdf: 1666755 bytes, checksum: fa3100a4126563ef9d7341d049583dba (MD5) Previous issue date: 2005 / Resumo: O presente trabalho teve como objetivo estudar a cinética de desidratação osmótica de pedaços de melão em soluções de sacarose e maltose, avaliando-se parâmetros de textura e cor ao longo do processo. Cubos de melão da variedade Cucumis melo inodorus, cultivar Gold Mine, de 20 mm foram imersos em soluções hipertônicas de sacarose ou maltose nas concentrações de 40 a 60°Brix e o processo foi conduzido por 8 horas com temperatura controlada (30 ou 40°C) e agitação de 120 rpm. Perda de água e de peso, incorporação de sólidos na fruta, atividade de água, cor e textura foram analisadas ao longo do processo em função da temperatura de tratamento, tipo e concentração da solução. O ponto final de equilíbrio e os coeficientes de difusão para a água e os açúcares foram estimados através de um modelo empírico da literatura, baseado na equação de Fick, comparando-se os efeitos da sacarose e da maltose na transferência de massa durante o processo. Para todos os ensaios, a perda de água e de peso aumentaram significativamente com a elevação da temperatura e da concentração da solução desidratante, entretanto os ensaios com maltose promoveram uma maior taxa de saída de água da fruta e menor ganho de sólidos. As características de cor da fruta fresca permaneceram praticamente inalteradas pela desidratação osmótica, observando-se apenas uma intensificação da cor ocasionada pelo aumento dos valores do parâmetro b* e do croma C*, devido à concentração de pigmentos provocada pela perda de água ao longo do tempo. Em relação à textura, houve um aumento na natureza viscosa e perda de elasticidade durante o processo, por conseqüência da incorporação de sólidos, que causa uma plasticidade na estrutura, porém a maltose se mostrou mais efetiva na manutenção das características de textura da fruta fresca. Foram selecionadas as condições mais favoráveis para cada uma das respostas estudadas, com o intuito de se realizar uma análise sensorial, sendo que, especificamente para estes ensaios, o tempo de tratamento foi de duas horas, determinado a partir das cinéticas de perda de água, ganho de sólidos e textura. Os resultados da avaliação sensorial revelaram que a desidratação osmótica forneceu um produto com boa aceitação pelo consumidor. / Abstract: The objective of this work was to study the osmotic dehydration kinetics of melon pieces in two types of solution (sucrose and maltose), with simultaneous evaluation of texture and color parameters all along the process. Melon (Cucumis melo inodorus, cultivar Gold Mine) cubes of 20 mm were immersed in hypertonic solution of sucrose or maltose with different concentrations (40 to 60°Brix) and the process was carried out for eight hours under controlled temperature (30°C or 40°C) and agitation (120 rpm). Water and weight loss, solids gain, water activity, color and texture were analysed throughout the process as a function of temperature, osmotic agent and solution concentration. The final equilibrium point and the diffusion coefficients for water and sugar were estimated using an empiric model from literature based on Fick's unsteady law of diffusion in order to compare sucrose and maltose effects in mass transfer rates during the osmotic process. For all treatments, water removal and weight loss increased at a significant level for higher temperature and solution concentrations, but the greatest water loss rate and lowest sugar uptake was verified when using maltose solutions. The color fresh-like characteristics were practically kept by the osmotic dehydration, with a slightly color intensification due to an increase on the b* parameter and on chrome values, as a consequence of fruit pigments concentration, caused by water loss. For the texture, an increase of viscous nature of fruit and elasticity loss was observed, indicating that the sugar impregnation occurred along the process provoked a plasticity in fruit structure. Maltose showed to be more effective on fruit texture maintenance. The best conditions for each one of the response variables were selected and the final product was evaluated by a sensorial analysis. The treatment time for these tests was two hours, determined by water loss, solids gain and texture kinetics. Sensorial results revealed that osmotic dehydration provided a good product acceptance by the consumer / Mestrado / Engenharia de Alimentos / Mestre em Engenharia de Alimentos

Les matériaux basés sur le système Fe-Ni-Cr utilisés à haute température doivent présenter une bonne résistance à l'oxydation, généralement obtenu par la croissance lente d’une couche d’oxyde de chrome à la surface de ces alliages. Pour prédire la formation d'une couche d’oxyde protectrice la perméabilité de l'oxygène dans l’alliage doit être connue, la perméabilité étant définie comme le produit de la solubilité et du coefficient de diffusion de l’oxygène. L'objectif de nos travaux est de mesurer la perméabilité, la solubilité et la diffusivité de l'oxygène dans des alliages Fe-Ni pour des températures supérieures à 1000°C. Afin d'obtenir les meilleurs résultats,la formation d'une couche externe d'oxyde pendant les expériences doit être évitée. Pour cela, la pression partielle d'oxygène a été fixée à la pression d'équilibre Fe/FeO dans toutes les expériences. En outre, afin d'étudier l'effet de la vapeur d'eau sur la perméabilité, la solubilité et la diffusivité de l’oxygène, deux atmosphères ont été utilisées: l’une considérée comme sèche et l’autre comme humide. L'atmosphère sèche a été obtenue en utilisant la technique du « pack de Rhines »: les échantillons sont oxydés dans des capsules en quartz sous vide qui contiennent un mélange de poudre de fer et de wüstite. L'atmosphère humide a quant à elle été obtenue en utilisant des mélanges gazeux H2/H2O avec un ratio approprié de vapeur d'eau et d’hydrogène afin de fixer la pression partielle d’oxygène à la pression d’équilibre Fe/FeO. Les mesures de solubilité réalisées dans ce travail ont montré que celle-ci atteint son maximum dans le fer pur et diminue avec l’ajout de nickel. Cependant, la dépendance de la solubilité avec la composition de l’alliage Fe-Ni n'est pas idéale et ne peut être prédite à partir de modèles simples. De plus, les résultats obtenus sous atmosphère humide suggèrent que la présence de vapeur d'eau dans l'atmosphère augmente la solubilité de l'oxygène d’un facteur 2 dans les alliages avec une concentration en nickel inférieure ou égale à 60 at.% pour des températures proches de 1000°C,tandis qu'à 1150°C, la solubilité de l'oxygène est indépendante de l'environnement. La perméabilité de l'oxygène a été déterminée en mesurant la cinétique d'oxydation interne d'alliages Fe-Ni-Cr. Les résultats ont montré que la perméabilité de l'oxygène présente les mêmes variations avec la composition de l’alliage que la solubilité de l'oxygène, indépendamment de l'atmosphère.De plus, aucun effet significatif de la vapeur d'eau sur les valeurs de perméabilité de l'oxygène n'a été observé. Le coefficient de diffusion de l'oxygène a également été déterminé en utilisant les résultats précédents, c’est à dire la perméabilité et la solubilité de l’oxygène mesurées dans notre étude. Pour une température supérieure à 1000°C, la variation du coefficient de diffusion de l'oxygène avec la composition de l'alliage est similaire dans tous les environnements testés et un maximum est observé pour les alliages avec une teneur en nickel de 40 at.%. Cependant, la présence de vapeur d'eau dans l'atmosphère diminue les valeurs du coefficient de diffusion de l'oxygène, par un facteur 2-3 à 1000°C, pour les alliages avec une concentration en nickel inférieure ou égal à 60 at.%. De plus, il a été trouvé que la différence entre les coefficients de diffusion mesurés dans l’atmosphère sèche et humide augmente à mesure que la température diminue. En conclusion, il a été constaté que la vapeur d'eau n'a aucun effet sur la manière dont la perméabilité, la solubilité et la diffusivité de l'oxygène varient avec la composition des alliages Fe-Ni. Cependant, la présence de vapeur d'eau dans l'environnement semble augmenter la solubilité de l'oxygène et diminuer sa diffusivité dans les alliages riches en fer. De plus, l’effet de la vapeur d’eau apparaît plus important aux plus basses températures étudiées. / It is a worldwide priority to reduce emissions of greenhouse gases such as CO2. One solution for reducing these emissions is to improve the efficiency of energy production units by increasing their operating temperature. However, in order to increase operating temperature, new austenitic materials based on the Fe-Ni-Cr system have to be designed. In addition, these materials need to exhibit good protection against high temperature oxidation, which is achieved by the formation of a slow growing chromium oxide or alumina scale on the metal. However, to predict the formation of a protective scale, knowledge of the oxygen permeability, the product of oxygen solubility and diffusivity, in the base alloy is required. The objective of this study is to measure the permeability, solubility and diffusivity of oxygen in Fe- Ni alloys at temperatures above 1,000°C. In order to obtain the best results, the formation of an external oxide layer during the experiment has to be avoided. To achieve this, the oxygen partial pressure was fixed at the Fe/FeO equilibrium pressure in all experiments. In addition, two types of atmospheres were used: one dry and one wet, in order to investigate the effect of water vapour on oxygen permeability, solubility and diffusivity. The dry atmosphere was achieved using the Rhines Pack technique. The samples were oxidised in vacuum-sealed quartz capsules, which contained a mixture of powdered iron and wüstite. The humid atmosphere was obtained by using H2/H2O gas mixtures with the appropriate water vapour to hydrogen ratio to fix oxygen partial pressure at the Fe/FeO equilibrium. The maximum oxygen solubility was found in pure iron, and decreased continuously with nickel additions to the alloy. The dependence of solubility on alloy composition is non-ideal, and cannot be predicted from simple models. Moreover, the presence of water vapour in the atmosphere seems to increase the solubility by a factor of 2 in alloys with nickel content lower than 80 at.% at temperatures near 1,000°C. However, at 1,150°C the solubility of the oxygen is independent of the environment. The oxygen permeability was determined by measuring the internal oxidation kinetics of Fe-Ni-Cr alloy. These kinetics were evaluated by measuring the internal oxidation zone depth by optical microscopy, or by continuous and discontinuous thermogravimetry. Results showed that the oxygen permeability exhibits the same variation with alloy composition as the oxygen solubility, independent of the atmosphere. In particular, no significant effect of water vapour on oxygen permeability values was observed. In the present study, the oxygen diffusion coefficient was also determined using permeability, in addition to the independent measurement of the oxygen solubility carried out in the present study. For temperature above 1,000°C, the variation of oxygen diffusion coefficient with the alloy composition is similar in all environments tested, and a maximum is observed for alloys with a nickel content of 40 at.%. However, for a given nickel content up to 60 at.%, the presence of water vapour in the atmosphere decreases the value of the oxygen diffusion coefficient by a factor of 2-3 at 1,000°C. In addition, this difference between diffusion coefficients measured in a dry and wet atmosphere increases as the temperature decreases. Overall, it was found that the water vapour has no effect on the way in which oxygen permeability, solubility and diffusivity vary with the alloy composition. However, the presence of water vapour in the environment appears to increase the oxygen solubility and decrease the oxygen diffusivity in iron-rich alloys, the effect being more significant at low temperatures. These results suggest further research into interactions between O, H and metal vacancies, particularly for temperature around 1,000°C and below, as the latter defect is thought to change the diffusion and solubility properties of interstitial species.

Zeolite membranes are considered to be a promising alternative to polymeric membranes and they have the potential to separate gases under harsh conditions. Silicalite-1 membranes in particular are easy to prepare and suitable for several industrial applications. In this research project, silicalite-1/ceramic composite membranes were prepared using the pore plugging hydrothermal synthesis method and supports with zirconium oxide and/or titanium oxide as active layers. The effect of the support’s pore size on the morphology and permeation performance of the prepared membranes was investigated using five supports with different active layer pore sizes in the range of 0.14 – 1.4 m. The prepared membranes were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), electron diffraction spectrometer (EDS), single gas and binary gas mixtures permeation tests. The results confirmed the presence of a typical silicalite-1 zeolite structure with a high internal crystalline order grown inside the pores of the active layer of the supports, with a dense film covering most of the supports active layers. Silicalite-1 crystals in the prepared membranes were preferably oriented with either a- or b-axes perpendicular to the support surface. Single gas permeation results illustrated that the observed permeances were not directly related to the kinetic diameter of permeants. Instead, the transport of the studied gases through the prepared membranes occurred by adsorption followed by surface diffusion mechanism. Binary gas tests performed with CO2 and N2 mixtures showed that the prepared membranes were selective and very permeable with CO2/N2 permselectivities up to 30 and a CO2 permeances in the order of 10-6 mol m-2 Pa-1 s-1. A model was developed, based on Maxwell−Stefan equations and Extended Langmuir adsorption isotherm, to describe the transport of binary CO2 and N2 mixtures through the prepared silicalite-1 membranes. The model results showed that the exchange diffusivities (D12 and D21) were less dependent on the feed pressure and feed composition compared to the permeances and the permselectivities. Hence, they are more appropriate to characterize the intrinsic transport properties of the prepared silicalite-1 membranes.

Foam fractionation is an adsorptive bubble separation technology that has shown potential as a replacement to the more costly and non-sustainable traditional downstream processing methods such as solvent extraction and chromatography for biological systems. However biological systems mostly tend to be a mixture of surface active species that complicates the foam fractionation separation. In this thesis a detailed experimental study on the application of foam fractionation to separate a well-defined surfactant-protein mixture was performed with emphasis on the competitive adsorption behaviour and transport processes of surfactant-protein mixtures in a foam fractionation process. Surface tension and nuclear magnetic resonance (NMR) measurements showed that nonionic surfactant Triton X−100 maximum surface pressure, surface affinity and diffusivity were a factor of 2.05, 67.0 and 19.6 respectively greater than that of BSA. Thus Triton X−100 dominated the surface adsorption at an air-water surface by diffusing to the surface and adsorbing at the surface faster than BSA. This competitive adsorption behaviour was observed in foam fractionation experiments performed for Triton X−100/BSA mixtures for different feed concentration ratios and air flow rates. The recovery and enrichment of Triton X−100 were found to increase and decrease respectively with increasing air flow rate for all foam fractionation experiments as expected for a single component system. However the recovery and enrichment of BSA were both found to increase with increasing air flow rate for high feed concentrations of Triton X−100.Bubble size measurements of the foamate produced from foam fractionation experiments showed that at steady state conditions the bubbles rising from the liquid pool were stabilised by BSA. However at the top of the column the recovery of Triton X−100 in the foamate (75% to 100%) was always greater than the recovery of BSA (13% to 76%) for all foam fractionation experiments. In addition, for high feed concentrations of both components and at low air flow rates, the enrichment of BSA remained at almost unity for most experiments and only increased when the recovery of Triton X−100 reached 100%. Thus it was concluded that Triton X-100 displaced the adsorbed BSA from the surface. The foam drainage properties of Triton X−100/BSA mixtures were characterised using two methods; forced foam drainage and from pressure profiles of steady state foam fractionation experiments (pressure method). The drainage data from the forced foam drainage was found not to be compatible with experimental foam fractionation results, by indicating that stable foam was not produced during the foam fractionation experiments. However stable foam was repeatedly produced during foam fractionation experiments. The drainage data from the pressure method was found to be in close agreement to experimental foam fractionation experiments. The work in this thesis takes a significant step beyond the literature experimental foam fractionation studies for multicomponent systems. In addition to investigating the effect of foam fractionation process parameters on the separation of mixed systems, the results from the characterisation studies of surface adsorption and foam properties provided insight and deeper understanding of the competitive adsorption behaviour of surfactants and proteins in a foam fractionation process.

Knowledge of the full 5-degree Grain Boundary Character Distribution (GBCD) is vital to understanding properties, such as gas diffusivity, that are dominated by grain boundary character. Surface characterization techniques, such as Electron Backscattered diffraction (EBSD), can provide only 4 of the 5 GB characteristics (the rotation between the neighboring grains, and the trace of the GB on the surface). The inclination of the GB in the direction normal to the surface is not known. A previous study indicated that the GB inclination could be recovered by correlating the Electron Backscattered patterns (EBSPs) of sample points near the GB with EBSPs taken from the centers of the neighboring grains. The resultant transition curve could be compared with theoretical curves obtained from MonteCarlo simulations of electron yield from the two grains. However, a practical method based upon this study was never implemented. Here, a few microscopy and image filters have been applied to the EBSPs to improve the image quality. Also, several experiments have been conducted to verify and validate the interaction volume of the materials used to produce theoretical transition curves, in order to receive more accurate results. In this work, it is hypothesized that transition curves obtained from considering individual band intensities from the EBSPs will give more informative transition curves. The filtered EBSPs from the band intensities coupled with the accurate interaction volume values, should give us more reliable and repeatable transition curves, and that a more detailed comparison of the experimental and simulated transition curves will give higher fidelity results, in terms of GB inclination determination.

Thermal diffusivity in an important thermophysical property that quantifies the ratio of the rate at which heat is conducted through a material to the amount of energy stored in a material. The pulsed laser diffusion (PLD) method is a widely used technique for measuring thermal diffusivities of materials. This technique is based on the fact that the diffusivity of a sample may be inferred from measurement of the time-dependent temperature profile at a point on the surface of a sample that has been exposed to a pulse of radiant energy from a laser or flash lamp. An accepted standard approach for the PLD method is based on a simple model of a PLD measurement system. However, the standard approach is based on idealizations that are difficult to achieve in practice. Therefore, models that treat a PLD measurement system with greater fidelity are desired. The objective of this research is to develop and test a higher fidelity model that more accurately represents the spatial and temporal variations in the input power. This higher fidelity model is referred to as Distributed Source Finite Absorption (DSFA) model. The cost of the increased fidelity associated with the DSFA model is an increase in the complexity of inferring values of the thermal diffusivity. A new method of extracting values from time dependent temperature measurements based on a genetic algorithm and on reduced order modeling was developed. The primary contribution of this thesis is a detailed discussion of the development and numerical verification of this proposed new method for measuring the thermal diffusivity of various materials. Verification of the proposed new method was conducted using numerical experiments. A detailed model of a PLD system was created using advanced engineering software, and detailed simulations, including conjugate heat transfer and solution of the full Navier-Stokes equations, were used to generate multiple numerical data sets. These numerical data sets were then used to infer the thermal diffusivity and other properties of the sample using the proposed new method. These numerical data sets were also used as inputs to the standard approach. The results of this verification study show that the proposed new method is able to infer the thermal diffusivity of samples to within 4.93%, the absorption coefficient to within 10.57 % and the heat capacity of the samples to within 5.37 %. Application of the standard approach to these same data sets gave much poorer estimates of the thermal diffusivity, particularly when the absorption coefficient of the material was relatively low.

The structure and spatial arrangement of grain boundaries strongly affect the properties of polycrystalline materials such as corrosion, creep, weldability, superconductivity, and diffusivity. However, constructing predictive grain boundary structure-property models is taxing, both experimentally and computationally due to the high dimensionality of the grain boundary character space. The purpose of this work is to develop an effective method to infer grain boundary structure-property models from measurement of the effective properties of polycrystals by utilizing the inverse problem theory. This study presents an idealized case in which structure-property models for grain boundary diffusivity are inferred from a noisy simulation. The method presented in this study is derived from a general mathematical expression of inverse problem theory. The derivation of the method is carried step by step by considering diffusivity as the property of interest. The use of the Bayesian probability approach in the inference method makes the uncertainty quantification possible to perform. This study demonstrates how uncertainty quantification for the inferred structure-property models is easily performed within the idealized case framework. The method of quantifying the uncertainty is carried by utilizing the Metropolis-Hastings algorithm and Kernel Density Estimation method. The validation of the method is carried out by considering structure-property models with one, three, and five degrees of freedom. Two- and three-dimensional simulated polycrystals are used in this study to obtain the simulation data. The two-dimensional simulated polycrystals used in this study are generated using grain growth simulation performed using a front-tracking algorithm. The three-dimensional polycrystals used in this study are generated using Neper software resulting in a real-like polycrystals. The structure-property models used in the validation are picked by considering the qualitative features that reflect trends observed in literature. The inference method is performed by ignoring any knowledge about the structure-property model in the process.

In the near future, Gen II, III, and IV nuclear reactors will be in operation. UO2 is a common fuel for reactors in each of these generations and molten salts are used as coolant/fuel in Gen IV molten salt reactors. This thesis investigates potential ways to measure thermal conductivity for these materials: Raman thermometry for UO2 and a needle probe for molten salts. Four Raman thermometry techniques are investigated in this thesis: The Two Laser Raman (TLR), Time Differential Domain Raman (TDDR), Frequency Resolved Raman (FRR), and Frequency Domain Raman (FDR). The TLR is a steady state method used with a thin film. The TDDR and FRR are both time domain methods used with thin cantilever samples. The FDR is a frequency domain method used with a thermally thick sample. Monte Carlo like simulations are performed for each technique. In the simulations, the affect introduced uncertainty has on the measurement of thermal conductivity and thermal diffusivity is measured. From the results, it is recommended that the TLR should be used for measuring thermal conductivity and the FRR used for measuring thermal diffusivity. The TDDR and FDR were heavily affected by the uncertainty which resulted in inconsistent measured thermal properties. For measuring the thermal conductivity of molten salt, a needle probe was designed and manufactured to withstand the corrosive environment found in using molten salts. The probe uses modulated joule heating and measures the temperature rise in a thermocouple. The phase delay and temperature amplitude of the thermocouple are used in determining the thermal conductivity. A new thermal quadrupole based analytical solution, which takes into consideration convection and radiation, to the temperature rise of the probe is presented. The analytical solution is verified using a numerical solution found using COMSOL. Preliminary data was obtained with the probe in water.

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