Membrane Distillation (MD) is a very promising new technology which can be coupled with renewableenergies and/or waste heat to produce pure water at a low-cost. MD is extremely dependent upon theperformance of the membrane, as it dictates the mass transfer, the heat transfer and the long-termapplication. Unfortunately, there are no commercially produced MD-specific membranes at this point intime. This project aims at finding correlations between membrane characteristics and their performancesin order to define the optimal morphologies and operating conditions for a MD-specific membrane. Todo so, the characteristics of 3 PTFE membranes initially designed for MF were determined throughporosity measurements and microscopic imaging, while their performances were evaluated by measuringthe air permeability and by testing them on an AGMD bench-scale unit.It was found that the most desirable characteristics for a membrane with a high flux are a film with largeporosity, low tortuosity, a small thickness with a resistance to compaction and that has not been subjectedto thickness altering processes. Moreover, the surface pore sizes need to be small enough to avoid surfacewetting, and the backing layer should not restrict the vapor flow in a significant way and should possesslarge open areas.As the feed water temperature and/or the flow rate rises, the flux increases and the energy requirementdecreases, this means that one should ideally aim for the highest possible operating conditions whichrequires larger costs. Therefore it is necessary to find a cost effective solution for each application.The results show that, for comparative purposes, Gurley values are good indicators of a membrane’soverall performance in MD, despite the fact that it does not always accurately predict it. It has also beenfound that membrane specifications provided by manufacturers are generally only approximations, andshould therefore not be used as very precise data for comparing membranes.

No description available.

Yes / CO2 capture from natural gas was experimentally and theoretically studied using a dead-end polymeric permeation cell. A numerical model was proposed for the separation of CO2/CH4 using Polytetrafluoroethylene (PTFE) in a flat sheet membrane module and developed based upon the continuity, momentum and mass transfer equations. The slip velocity condition was considered to show the reflection of gas flow in contact with the membrane surface. The solution method was based on the well-known SIMPLE algorithm and implemented using MATLAB to determine the velocity and concentration profiles. Due to change in velocity direction in the membrane module, the hybrid differencing scheme was used to solve the diffusion-convection equation. The results of the model were compared with the experimental data obtained as part of this work and good agreement was observed. The distribution of CO2 concentration inside the feed and permeate chambers was shown and the velocity profile at the membrane surface was also determined using reflection factor for polymericmembrane. The modelling result revealed that increasing the amount of CO2 in gas feed resulted in an increase in the CO2 in the permeate stream while the gas feed pressure increased. By changing the permeability, the model developed by use of the solution-diffusion concept could be used for all polymeric membranes with flat sheet modules.

No description available.

No description available.

Este trabalho apresenta um estudo dos processos de prensagem e sinterização do politetrafluoretileno (PTFE) com o objetivo principal de investigar a influência dos parâmetros desses processos na microestrutura e nas propriedades mecânicas do material após sinterização. O PTFE faz parte do grupo dos termoplásticos, mas assim como outros polímeros de alto peso molecular, apresenta elevada viscosidade no estado fundido que impede sua utilização em moldagem por injeção, e seu processamento é realizado por compactação a frio do pó polimérico seguida de sinterização. No processo de sinterização é aplicado um tratamento térmico acima da temperatura de fusão do material que é responsável por grandes deformações anisotrópicas que, por sua vez, são dependentes do histórico de carregamentos induzidos na fase de compactação. Com o objetivo de desenvolver modelos de comportamento termomecânicos para realizar simulações computacionais dessas etapas de fabricação, ensaios experimentais foram realizados para se investigar os diferentes mecanismos de evolução microestrutural e de deformações nas etapas de compactação e sinterização. O estudo experimental do processo de compactação compreendeu a realização de ensaios de compactação uniaxial (oedométrico), de compactação hidrostática em prensa isostática e ensaios triaxiais verdadeiros em um dispositivo original acoplado numa prensa triaxial com seis atuadores eletrohidráulicos. Através dos resultados obtidos dos ensaios de compactação foi possível identificar os parâmetros do modelo de Drucker-Prager/cap, disponível na biblioteca de leis de comportamento do programa de cálculo pelo método dos elementos finitos ABAQUSTM, que permitiu de simular numericamente alguns casos simples. O estudo experimental do processo de sinterização foi realizado com o auxílio de ensaios de termogravimetria (TGA), calorimetria exploratória diferencial (DSC) e ensaios de dilatometria em corpos-de-prova isótropos e anisótropos com diferentes índices de vazios. Através dos resultados obtidos destes ensaios foi possível identificar que a deformação global de sinterização é composta por uma deformação térmica reversível, uma deformação devido à mudança de fase cristalina em fase amorfa -ou vice-versa-, uma deformação devido ao fechamento dos vazios e uma deformação de recuperação. Este estudo foi realizado em dois tipos de materiais, sendo o PTFE puro e o PTFE reforçado com 5wt% de EkonolTM e 5wt% de fibras de carbono, respectivamente comercializados pelos nomes de TeflonTM 6407 e TeflonTM 6507. / The main objective of this work is to study the influence the process parameters on the microstructure and the mechanical properties of components manufactured by compaction at room temperature and sintering of polytetrafluorethylene (PTFE). Similary to other High Molecular Weight Polymers and although it belongs to the group of thermoplastic polymers, since it cannot be processed in the melt state because its very high viscosity, PTFE, is powder processed -that consists in sintering compacted powder-. Sintering corresponds to a heat treatment up to temperatures higher than the melting temprature, inducing finite deformations that are generally anistropic and dependent on the mechanical loading the material has been submitted to during the pre-compaction at room temperature. In order to develop thermo-mechanical constitutive equations that could be used during predictive numerical simulations of the whole process, different tests have been performed to study the different mechanisms that are responsible for microstructural evolutions and deformations during compaction and sintering. The experimental study of the compaction has been performed via uniaxial (oedometric) compaction tests, hydrostatic compaction tests that were made with an isostatic hydraulic press and triaxial tests that were made with and original device installed on an electrohydraulic testing machine six actuators. A \"Drucker-Prager/cap\" type elasto-plastic model -as available in the constitutiveequations library of ABAQUSTM industrial finite element software- has been identified from the results of these tests, so that a few simple cases have been numerically simulated. The experimental study of the sintering process has been performed via Thermo-Gravimetric Analyses (TGA), Differential Scanning Calorimetric analyses (DSC) and dilatometry tests that were performed on isotropic or anisotropic specimens with different values of the porosity From the results of these tests it has been possible to decompose the sintering deformation into different mechanisms, viz. a reversible thermal expansion, a strain that is linked to the transition from the crystalline phase to the amorphous phase -or vice versa-, a pore closure strain and a recovery strain. This study has been performed on a powder made of pure PTFE and a powder of PTFE filed with 5wt% EkonolTM and 5wt% of carbon fibres, respectively available as TeflonTM 6407 and TeflonTM 6507.

Made available in DSpace on 2014-12-17T14:58:15Z (GMT). No. of bitstreams: 1 MayaraSCFL_DISSERT.pdf: 5165682 bytes, checksum: c5b249c3b897f27db4e517452be9b9ce (MD5) Previous issue date: 2012-04-30 / Coordena??o de Aperfei?oamento de Pessoal de N?vel Superior / Composites based on PEEK + PTFE + CARBON FIBER + Graphite (G_CFRP) has increased application in the top industries, as Aerospace, Aeronautical, Petroleum, Biomedical, Mechanical and Electronics Engineering challenges. A commercially available G_CFRP was warmed up to three different levels of thermal energy to identify the main damage mechanisms and some evidences for their intrinsic transitions. An experimental test rig for systematize a heat flux was developed in this dissertation, based on the Joule Effect. It was built using an isothermal container, an internal heat source and a real-time measurement system for test a sample by time. A standard conical-cylindrical tip was inserted into a soldering iron, commercially available and identified by three different levels of nominal electrical power, 40W (manufacturer A), 40W (manufacturer B), 100W and 150W, selected after screening tests: these power levels for the heat source, after one hour of heating and one hour of cooling in situ, carried out three different zones of degradation in the composite surface. The bench was instrumented with twelve thermocouples, a wattmeter and a video camera. The twelve specimens tested suffered different degradation mechanisms, analyzed by DSC (Differential Scanning Calorimetry) and TG (Thermogravimetry) techniques, Scanning Electron Microscopy (SEM) and Energy-Dispersive X-Rays (EDX) Analysis. Before and after each testing, it was measured the hardness of the sample by HRM (Hardness Rockwell M). Excellent correlations (R2=1) were obtained in the plots of the evaporated area after one hour of heating and one hour of cooling in situ versus (1) the respective power of heat source and (2) the central temperature of the sample. However, as resulting of the differential degradation of G_CFRP and their anisotropy, confirmed by their variable thermal properties, viscoelastic and plastic properties, there were both linear and non-linear behaviour between the temperature field and Rockwell M hardness measured in the radial and circumferential directions of the samples. Some morphological features of the damaged zones are presented and discussed, as, for example, the crazing and skeletonization mechanism of G_CFRP / Comp?sitos baseados em matrizes polim?ricas de PEEK e PTFE, refor?adas com fibra de carbono e grafite (G_CFRP) apresentam crescente aplica??o e desafios ? Engenharia nas ind?strias Aeroespacial, Aeron?utica, de Petr?leo, Biom?dica, Mec?nica e Eletr?nica. Um comp?sito G_CFRP foi aquecido em tr?s n?veis de energia t?rmica para identificar os principais mecanismos de dano e algumas evid?ncias em suas transi??es de mecanismos. Uma bancada experimental foi desenvolvida para sistematizar o fluxo t?rmico com base no Efeito Joule. Foi constru?da usando-se um recipiente isot?rmico, uma fonte quente interna e um sistema de medidas em tempo real para ensaiar um corpo-de-prova (CP) de cada vez. Uma ponta c?nica-cil?ndrica foi inserida em um ferro de soldar, comercialmente dispon?vel e identificado por tr?s diferentes n?veis de pot?ncia el?trica, 40W (fabricante A), 40W (fabricante B), 100W e 150W, selecionados ap?s ensaios piloto: estes n?veis de pot?ncia para a fonte quente, ap?s uma hora de aquecimento e uma hora de resfriamento in situ, promoveu tr?s zonas diferentes de degrada??o na superf?cie do comp?sito. A bancada foi instrumentada com doze termopares, um watt?metro e uma c?mera de v?deo. Os doze C.P. ensaiados apresentaram diferentes mecanismos de degrada??o, analisados pelas t?cnicas de Calorimetria Diferencial Explorat?ria (DSC) e Termogravimetria (TG), e pelas an?lises de Microscopia Eletr?nica de Varredura (MEV) e Energia Dispersiva de Raios-X (EDS). Antes e ap?s cada ensaio, foram feitos ensaios de dureza Rockwell M (HRM). Excelentes correla??es (R2=1) foram obtidas nas curvas da ?rea evaporada ap?s uma hora de aquecimento e uma hora de resfriamento in situ versus (1) a respectiva pot?ncia da fonte quente e (2) a temperatura central do C.P. entretanto, como resultado da degrada??o diferencial do G_CFRP e da sua anisotropia, confirmadas por suas propriedades t?rmicas vari?veis, propriedades viscoel?sticas e viscopl?sticas, houve comportamentos linear e n?o-linear entre o campo de temperatura e a HRM medidos nas dire??es radial e circunferencial dos C.P. Algumas peculiaridades morfol?gicas das zonas de dano s?o apresentadas e discutidas, como, por exemplo, os mecanismos de dano por crazing e esqueletiza??o do G_CFRP

Este trabalho apresenta um estudo dos processos de prensagem e sinterização do politetrafluoretileno (PTFE) com o objetivo principal de investigar a influência dos parâmetros desses processos na microestrutura e nas propriedades mecânicas do material após sinterização. O PTFE faz parte do grupo dos termoplásticos, mas assim como outros polímeros de alto peso molecular, apresenta elevada viscosidade no estado fundido que impede sua utilização em moldagem por injeção, e seu processamento é realizado por compactação a frio do pó polimérico seguida de sinterização. No processo de sinterização é aplicado um tratamento térmico acima da temperatura de fusão do material que é responsável por grandes deformações anisotrópicas que, por sua vez, são dependentes do histórico de carregamentos induzidos na fase de compactação. Com o objetivo de desenvolver modelos de comportamento termomecânicos para realizar simulações computacionais dessas etapas de fabricação, ensaios experimentais foram realizados para se investigar os diferentes mecanismos de evolução microestrutural e de deformações nas etapas de compactação e sinterização. O estudo experimental do processo de compactação compreendeu a realização de ensaios de compactação uniaxial (oedométrico), de compactação hidrostática em prensa isostática e ensaios triaxiais verdadeiros em um dispositivo original acoplado numa prensa triaxial com seis atuadores eletrohidráulicos. Através dos resultados obtidos dos ensaios de compactação foi possível identificar os parâmetros do modelo de Drucker-Prager/cap, disponível na biblioteca de leis de comportamento do programa de cálculo pelo método dos elementos finitos ABAQUSTM, que permitiu de simular numericamente alguns casos simples. O estudo experimental do processo de sinterização foi realizado com o auxílio de ensaios de termogravimetria (TGA), calorimetria exploratória diferencial (DSC) e ensaios de dilatometria em corpos-de-prova isótropos e anisótropos com diferentes índices de vazios. Através dos resultados obtidos destes ensaios foi possível identificar que a deformação global de sinterização é composta por uma deformação térmica reversível, uma deformação devido à mudança de fase cristalina em fase amorfa -ou vice-versa-, uma deformação devido ao fechamento dos vazios e uma deformação de recuperação. Este estudo foi realizado em dois tipos de materiais, sendo o PTFE puro e o PTFE reforçado com 5wt% de EkonolTM e 5wt% de fibras de carbono, respectivamente comercializados pelos nomes de TeflonTM 6407 e TeflonTM 6507. / The main objective of this work is to study the influence the process parameters on the microstructure and the mechanical properties of components manufactured by compaction at room temperature and sintering of polytetrafluorethylene (PTFE). Similary to other High Molecular Weight Polymers and although it belongs to the group of thermoplastic polymers, since it cannot be processed in the melt state because its very high viscosity, PTFE, is powder processed -that consists in sintering compacted powder-. Sintering corresponds to a heat treatment up to temperatures higher than the melting temprature, inducing finite deformations that are generally anistropic and dependent on the mechanical loading the material has been submitted to during the pre-compaction at room temperature. In order to develop thermo-mechanical constitutive equations that could be used during predictive numerical simulations of the whole process, different tests have been performed to study the different mechanisms that are responsible for microstructural evolutions and deformations during compaction and sintering. The experimental study of the compaction has been performed via uniaxial (oedometric) compaction tests, hydrostatic compaction tests that were made with an isostatic hydraulic press and triaxial tests that were made with and original device installed on an electrohydraulic testing machine six actuators. A \"Drucker-Prager/cap\" type elasto-plastic model -as available in the constitutiveequations library of ABAQUSTM industrial finite element software- has been identified from the results of these tests, so that a few simple cases have been numerically simulated. The experimental study of the sintering process has been performed via Thermo-Gravimetric Analyses (TGA), Differential Scanning Calorimetric analyses (DSC) and dilatometry tests that were performed on isotropic or anisotropic specimens with different values of the porosity From the results of these tests it has been possible to decompose the sintering deformation into different mechanisms, viz. a reversible thermal expansion, a strain that is linked to the transition from the crystalline phase to the amorphous phase -or vice versa-, a pore closure strain and a recovery strain. This study has been performed on a powder made of pure PTFE and a powder of PTFE filed with 5wt% EkonolTM and 5wt% of carbon fibres, respectively available as TeflonTM 6407 and TeflonTM 6507.

Among the materials that can be treated in order to impart superhydrophobic properties are many originally hydrophilic metals. For this, they must undergo a sequential treatment, including roughening and hydrophobic coating. This contribution presents various preparation routes along with various characterization methods, such as dynamic contact angle (DCA) measurements, scanning electron microscopy (SEM) and spectroscopic techniques (FT–IRRAS, XPS, EIS). Micro-rough surfaces of pure and alloyed aluminum were generated most easily by using a modifie Sulfuric Acid Anodization under Intensifie conditions (SAAi). This produces a micro-mountain-like oxide morphology with peak-to-valley heights of 2 μm and sub-μm roughness components. Additionally, micro-embossed and micro-blasted surfaces were investigated. These micro-roughened initial states were chemically modifie with a solution of a hydrophobic compound, such as the reactive f uoroalkylsilane PFATES, the reactive alkyl group containing polymer POMA, or the polymer Teflo ® AF. Alternatively, the chemical modificatio was made by a Hot Filament Chemical Vapor Deposition (HFCVD) of a PTFE layer. The latter can form a considerably higher thickness than the wet-deposited coatings, without detrimental leveling effects being observed in comparison with the original micro-rough surface. The inherent and controllable morphology of the PTFE layers represents an important feature. The impacts of a standardized artificia weathering (WTH) on the wetting behavior and the surface-chemical properties were studied and discussed in terms of possible damage mechanisms. A very high stability of the superhydrophobicity was observed for the f uorinated wet-deposited PFATES and Teflo ® AF coatings as well as for some of the PTFE layer variants, all on SAAi-pretreated substrates. Very good results were also obtained for specimens produced by appropriate mechanical roughening and PTFE coating.

Com o crescente uso de estruturas de membrana tensionada, as relações tensãodeformação do tecido utilizado em sua fabricação devem ser bem entendidas. Deste modo, esta dissertação apresenta um estudo sobre o comportamento mecânico de um tecido arquitetônico PTFE-vidro, ressaltando seu complexo mecanismo de deformação que engloba efeitos de anisotropia, não-linearidade física, troca de ondulações, histerese, remoção do espaçamento entre os fios e variação de temperatura. Diferentes métodos para modelagem do material foram estudados, com ênfase no modelo de material ortótropo representado por um funcional energia de deformação hiperelástico. Além disso, vários protocolos para ensaios de tração em tecidos recobertos foram analisados e uma série de ensaios biaxiais com amostras cruciformes foram realizados no Centro de Pesquisa e Desenvolvimento da Birdair, Inc. Um determinado funcional energia de deformação foi então ajustado aos dados de campo obtidos nestes testes, cujos resultados foram então comparados diretamente aos dados obtidos em campo e a um ajuste direto de uma superfície suave tensão-deformação. A performance do modelo ajustado não se encontra ainda em um patamar de aplicação industrial, entretanto este estudo permite um entendimento global dos mecanismos de deformação do tecido PTFEvidro, fornecendo também uma massa de dados consistentes que podem ser utilizados em situações práticas. / Considering the growing use of tensioned membrane structures, the stress-strain relation of the fabric used on its construction must be well understood. This dissertation presents a study of the mechanical behavior of a PTFE coated fiberglass fabric, emphasizing its complex strain mechanism which is influenced by the material anisotropy, physical non-linearity, crimp interchange, hysteresis, removal of yarn spacing and changes in temperature. Different material models were studied, focusing on an orthotropic material model represented by a hyperelastic strain energy function. Also, different test protocols were reviewed and a series of biaxial tests on cruciform samples were performed at the Birdair, Inc.s Research and Development Center. A strain energy function was adjusted to the collected data and than its results compared to the data itself and to another stress-strain function directly adjusted to the data. The performance of the strain-energy function chosen is not on a level of industrial application; however this study gives a global understanding of the PTFE coated fiberglass strain mechanism and also provides a consistent database that may be used on real situations.