Dissertations / Theses on the topic 'Capacitive flow'

The goal of this research was to develop acoustic sensors and actuators for microfluidic applications. To this end, capacitive micromachined ultrasonic transducers (cMUTs) were developed which generate guided acoustic waves in fluid half-spaces and microchannels. An interdigital transducer structure and a phased excitation scheme were used to selectively excite guided acoustic modes which propagate in a single lateral direction. Analytical models were developed to predict the geometric dispersion of the acoustic modes and to determine the sensitivity of the modes to changes in material and geometric parameters. Coupled field finite element models were also developed to predict the effect of membrane spacing and phasing on mode generation and directionality. After designing the transducers, a surface micromachining process was developed which has a low processing temperature of 250C and has the potential for monolithically integrating cMUTs with CMOS electronics. The fabrication process makes extensive use of PECVD silicon nitride depositions for membrane formation and sealing. The fabricated interdigital cMUTs were placed in microfluidic channels and demonstrated to sense changes in fluid sound speed and flow rate using Scholte waves and other guided acoustic modes. The minimum detectable change in sound speed was 0.25m/s, and the minimum detectable change in flow rate was 1mL/min. The unique nature of the Scholte wave allowed for the measurement of fluid properties of a semi-infinite fluid using two transducers on a single substrate. Changes in water temperature, and thus sound speed, were measured and the minimum detectable change in temperature was found to be 0.1C. For fluid pumping, interdigital cMUTs were integrated into microchannels and excited with phase-shifted, continuous wave signals. Highly directional guided waves were generated which in turn generated acoustic streaming forces in the fluid. The acoustic streaming forces caused the fluid to be pumped in a single, electronically-controlled direction. For a power consumption of 43mW, a flow rate of 410nL/min was generated against a pressure of 3.4Pa; the thermodynamic efficiency was approximately 5x10-8%. Although the efficiency and pressure head are low, these transducers can be useful for precisely manipulating small amounts of fluid around microfluidic networks.

Sensores capacitivos são amplamente utilizados em vários sistemas de medida, tanto na indústria como em laboratórios de pesquisa. Estes dispositivos medem variadas grandezas físicas, como deslocamento, força, pressão, densidade e concentração de substâncias em escoamentos bifásicos, entre outros. Sua aplicação vêm sendo utilizada há algum tempo de forma relativamente elementar, necessitando ainda de estudos específicos para entender a fundo o fenômeno de transferência de carga. A sonda proposta neste trabalho visa melhorar a aquisição do sinal capacitivo e obter uma medida precisa de fração volumétrica em condições bifásicas e trifásicas. Portanto, é necessário um circuito transdutor que transmita de forma precisa a capacitância registrada entre os eletrodos dos sensores até uma central de aquisição. Neste trabalho buscamos desenvolver um modelo de sonda para medir frações volumétricas in situ. Para tanto, apresentamos as etapas de calibração dos sensores, através de válvulas de fechamento rápido, e validamos a técnica sob determinadas condições e variados padrões de escoamento. Dois sensores de geometrias distintas (anéis e hélices) foram utilizados na composição da sonda capacitiva não intrusiva. Propõe-se a solução do sistema linear para medição direta de fração volumétrica em escoamento trifásico.
Capacitive sensors are widely employed in many measurement systems in both industry and laboratory activities. These devices measure several physical quantities such as displacement, forces, pressure, density and concentration of substances in two-phase flows. Their application in industry is still insipient, in part because specific studies are still necessary to properly understand the phenomenon of charge transfer. The goal of this research is the development of a non-intrusive double-sensor probe to on-line measurement of in-situ volumetric fractions in two and three-phase flows. Therefore, we present the calibration work, through quick-closing valves, and validation techniques under certain conditions and for different flows patterns. A transducer circuit to transmit the capacitance sign accurately from the sensors to the central acquisition was developed. Two sensors with different geometries (rings and helix) comprise the double-sensor capacitive probe. Finally, we propose the solution of a linear system for the direct measurement of in-situ volumetric fraction in three-phase flow.

Orientadores: Antonio Carlos Bannwart, Oscar Mauricio Hernandez Rodriguez
Tese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia Mecânica e Instituto de Geociências
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Resumo: Neste trabalho, é apresentado o desenvolvimento de uma nova técnica para a medição da espessura do filme de água com alta resolução espacial e temporal em escoamento óleo-água. É proposto o uso de um sistema de medição de capacitância elétrica para medir filmes finos de água na proximidade da parede do tubo. O sistema conta com um sensor planar e foi necessário determinar a melhor geometria via simulações baseadas no Método de Elementos Finitos (FEM) para o caso de escoamento óleo-água. As características comparadas foram a profundidade de penetração do campo elétrico no filme de água, a sensibilidade, a resolução espacial mínima e a resposta quase-linear. Padrões de escoamento óleo-água disperso e anular instável foram estudados numa tubulação vertical de 12 m de comprimento, feita de vidro, com 50,8 milímetros de diâmetro interno. Os fluidos usados foram óleo mineral (com densidade 828 kg/m3 e viscosidade 220 mPas) e água da torneira. O trabalho experimental foi realizado nas instalações de escoamento multifásico do Laboratório de Engenharia Térmica e Fluidos (NETeF) da EESC-USP. Foi medida a espessura média do filme de água usando o sistema capacitivo e uma câmera de vídeo de alta velocidade. Para obter a espessura do filme de água a partir das imagens, foi proposto um algoritmo de pré-processamento e um algoritmo de segmentação que combina vários métodos disponíveis na literatura. Os resultados experimentais do sensor capacitivo mostraram que o sistema pode medir espessuras entre 400 µm e 2200 µm. O escoamento anular instável é caracterizado por grandes flutuações na no sentido do escoamento e na direção do perímetro, e estruturas interfaciais grandes (gotas). Por sua vez, o escoamento disperso tem flutuações menores no sentido do escoamento e na direção do perímetro, e estruturas interfaciais menores (gotículas). Uma estrutura interfacial média no espaço e no tempo é proposta para modelar a interface entre a região próxima à parede do tubo e a região do núcleo, e sua análise foi feita no domínio do tempo e da frequência. Foram estudadas a amplitude, velocidade e o comprimento da estrutura interfacial em cada par transmissor-receptor do sensor. Foi possível estabelecer correlações para a velocidade das estruturas em escoamento de óleo em água
Abstract: The development of a new technique for high spatial and temporal resolution film thickness measurement in oil-water flow is presented. A capacitance measurement system is proposed to measure thin water films near to the wall pipe. A planar sensor was chosen for sensing and some geometries were compared using finite elements method (FEM). The penetration depth, the sensitivity, the minimum spatial resolution (high spatial resolution) and the quasi-linear curve were the analyzed characteristics. Dispersed and unstable-annular oil-water flows patterns were studied in a 12-m long vertical glass pipe, with 50.8 mm of internal diameter, using mineral oil (828 kg/m3 of density and 220 mPa s of viscosity) and tap water. The experimental work was carried out in the multiphase-flow facilities of The Thermal-Fluids Engineering Laboratory (NETeF) of EESC-USP. Experiments with a high-speed video camera and the proposed capacitance system were performed to obtain images of the oil-water flow near the pipe wall. A pre-processing enhancement algorithm and a combined segmentation algorithm are proposed and allowed the measurement of characteristic space and time averaged water film thickness. Experimental results of the capacitive technique showed that the system could measure thickness between 400 µm and 2200 µm. It was possible to recognize and characterize typical behaviors of the two different flow patterns studied. Unstable-annular flow can be described by huge fluctuations on the flow direction and perimeter direction, and big interfacial structures (drops). On the other hand, dispersed flow has tiny fluctuations on the flow direction and perimeter direction, and smaller interfacial structures (droplets). An interfacial structure is suggested in order to model the interface between wall and core regions and it was analyzed in time and frequency domains; amplitude, velocity and wavelength at each pair transmitter-receiver of the sensor were studied. Correlations for the interfacial structure velocity were found for dispersed oil-in-water flow and unstable-annular flow
Doutorado
Explotação
Doutora em Ciências e Engenharia de Petróleo
CAPES

This master´s thesis is focused on technological designing in a small company ENGITEC Motosport s.r.o. In first theoretical part of the thesis is this subject described in detail and analyzed in terms of economic and technical aspect. Next part describes the current state of the company and the production hall as well with keep on its current layout. In the following chapters is chosen piston-shaped component, which is manufactured by the company and three different variants of the piston production. Then one of them is selected, to which all related capacities calculations are made. In the final part of the thesis is proposed the relevant final layout of the hall and there is also the technical-economic evaluation of the most relevant variant included. Key words

Diploma thesis deal with the issue revitalization of water stream. Assessment and design of revitalization is done for watercourse Osoblaha, situated in the cadastral territory Osoblaha nad Studnice by Osoblaha. In diploma thesis were designed several of revitalization measures such as stone backfill, willow fence, groyne, casting willow cuttings to supplement the vegetation on river‘s banks, fish shelter and wirestone baskets (gabions). In the given section was designed pool and also was there designed boulder slip, which will replace present downflow step. After designing was made hydrotechnical calculations to demostrate preservation runoff conditions of present stream condition.

CAPES; ANP; FINEP; MCT; PETROBRAS
Escoamentos bifásicos são encontrados com frequência, em atividades industriais, como por exemplo, em reatores químicos e nas operações de produção e transporte de petróleo, onde escoamentos do tipo gás-liquido são os mais comuns. Esses são caracterizados pela passagem simultânea de dois fluidos imiscíveis em um duto, podendo tomar diversas formas ao longo da tubulação, chamado de padrão ou regime de escoamento. Em muitos casos, o tipo de escoamento determina a eficiência e segurança dos processos ou plantas onde tais ocorrem. Desta forma, a monitoração em tempo real de escoamentos bifásicos é de grande importância. O objetivo deste trabalho é desenvolver um sensor inteligente para monitoramento de escoamento bifásico. Foram selecionados dois parâmetros importantes de monitoração, o primeiro deles é a fração de gás e o segundo a velocidade de translação de bolhas. Para isso foi desenvolvido uma sonda capacitiva que explora a diferença da permissividade elétrica das fases para diferenciá-las. Além disso, uma eletrônica anteriormente desenvolvida foi aprimorada para tornar possível a medição de dois canais simultaneamente e o firmware modificado para realização do cálculo de fração de vazio e velocidades de forma embarcada. A resposta da sonda capacitiva desenvolvida não depende apenas da proporção volumétrica das fases, mas também da forma que estão distribuídas em seu interior, portanto simulações de campo elétrico pelo método de elementos finitos foram realizadas para o levantamento da resposta do mesmo. A resposta do sensor foi validada através de testes estáticos e em escoamentos em plantas controladas, onde os resultados foram comparados com os obtidos, em medidas simultâneas com o sensor wire-mesh, adotado como referência neste trabalho. Os resultados obtidos mostram que o sensor capacitivo é capaz de medir os parâmetros de forma satisfatória. Assim, este sensor pode ser empregado em trabalhos futuros como ferramenta simples para monitoração de escoamentos bifásicos.
Two-phase flow is frequently found in industrial activities, for instance in chemical reactors or during oil production and transport, where gas-liquid flow type is the most common. Such flow is characterized by the simultaneous passage of two immiscible fluids in a pipe. The fluids may assume various spatial distributions in a pipe, which are classified into flow regimes. In many cases, the type of flow determines the efficiency and safety of the processes or plants in which they occur. The objective of this work is to develop a smart sensor for real-time monitoring of two-phase flows. Here two important monitoring parameters were selected; the first is the gas void fraction and the second translational bubble velocities. To this aim, a capacitive probe was developed that exploits the difference in electrical permittivity of the phases. In addition, a previously developed electronics have been further developed to make it possible to measure two channels simultaneously and the firmware has been modified for performing the calculation of the two parameters directly in the embedded microcontroller. The response of the capacitive probe depends not only on the volume fraction of the phases, but it also depends on the way they are distributed inside the pipe. In order to account for this, electric field simulations by finite element method were performed to survey the sensor responses. The overall sensor response was validated by static tests and controlled flow experiments in a pilot plant. The measurement results were compared with those obtained by simultaneous measurements with a wire-mesh sensor which was adopted as reference in this study. The results show that the capacitive sensor is able of measuring the parameters satisfactorily. Hence, the sensor can be applied in future work as a simple tool for two-phase flows monitoring.

The aim of the thesis is to elaborate the technological project for non-rotary (plate) parts production based on requirements of TOS KUŘIM – OS, a.s. The literary studies from the area of machining technology and technological designing are in the first part of the thesis. The evaluation of the contemporary state of production and dividing of products into groups is made in the next part. The following part of the thesis is dealing with the design and analysis of designed variants of disposition, choosing the most suitable variant, its optimalization and evaluation by the help of capacitive calculation. The drawing documentation (material flow included) and technoeconomic evaluation is elaborated in the final part of the thesis.

ANP; FINEP; MCT
Os escoamentos bifásicos são encontrados em diversas aplicações industriais, dentre elas na indústria do petróleo como escoamentos gás-líquido em tubulações. O conhecimento da distribuição das fases no escoamento é importante para garantir a operação eficiente e segura de plantas e equipamentos. Na área acadêmica o conhecimento dessa distribuição de fases permite o estudo de fenômenos físicos, além de permitir o desenvolvimento, refinamento e validação de modelos de escoamento. Neste trabalho, foi desenvolvido e investigado o uso de um novo sensor de múltiplas medidas de capacitância para o imageamento direto de escoamentos bifásicos. As medidas são baseadas na diferença na permissividade elétrica entre as fases, ou seja, o sensor pode ser aplicado para investigação de substâncias não-condutivas como óleos e líquidos orgânicos. Com o intuito de aprimorar a geometria do sensor e prever seu comportamento foram realizadas simulações do comportamento elétrico do sensor pelo método dos elementos finitos. O sensor é composto por dois anéis de eletrodos, um anel é o transmissor e o outro anel é o receptor, o qual é segmentado onde cada segmento é individualmente interrogado por uma eletrônica de forma rápida e multiplexada. Desta forma as imagens são geradas e formadas pelos sinais dos eletrodos distribuídos de uma maneira a representar a geometria investigada, o que elimina a necessidade do uso de técnicas de reconstrução de imagens. O sensor é construído em uma placa de circuito impresso flexível que é acoplada na parede interna de uma seção do duto. Uma eletrônica associada é responsável por detectar as variações de capacitância. O sensor desenvolvido, em conjunto com a eletrônica utilizada, foi testado em escoamentos bifásicos estáticos e dinâmicos, horizontais e verticais. As imagens diretas foram geradas para estas diferentes situações, apresentando resultados satisfatórios quando comparado com um sensor de referência. A principal contribuição deste trabalho é a apresentação de uma nova ferramenta capaz de gerar imagens diretas de escoamentos compostos por líquidos não-condutivos sem a necessidade do uso de técnicas de reconstrução de imagens.
Two-phase flow is present in many industrial applications, among them in petroleum industry as gas-liquid flow in pipelines. The knowledge of the phase distribution in the pipe flow is important for the efficiency and safety of the plants. In the academia, the knowledge of this phase distribution allows the understanding of physical phenomena, as well as gives support for the development, refinement and validation of physical models. In this work, a novel capacitive array sensor has been developed and its use was investigated to image two-phase flow. The measuring principle is based on the difference between electrical permittivity of the phases. Therefore the sensor can be applied to electrically non-conductive substances such as oil and organic liquids. Several simulations based on Finite Element Method have been performed to improve the sensor geometry and predict its electrical behavior. The sensor consists of two copper rings being one emitter and one receiver ring. Receiver ring is divided into segments which are individually interrogated by the measuring electronics in a fast and multiplexed manner. In this way, images are directly generated from acquired signals of electrodes, in a way that visually represents the investigated geometry avoiding the use of some image reconstruction technique. The sensor is fabricated in a flexible printed-circuit board which is flush- mounted inside the pipe wall. A measuring electronics is responsible to detect the capacitance changes in the electrodes. The introduced sensor along with the associated electronics has been tested in static and dynamic two-phase flow, both horizontally and vertically. Direct images were generated in these different situations showing satisfactory results when compared to a reference sensor. Main contribution of this work is the introduction of a new measuring tool which is able to image flow (also containing electrically non-conducting fluids) with no need to apply image reconstruction techniques.

Cette thèse porte sur l’optimisation des stratégies de reroutage dans les réseaux de télécommunications. Plus précisément, l’objectif est de proposer ou d’adapter des mécanismes permettant de router le trafic du réseau après une panne partielle, c’est-à-dire, après une baisse de la bande passante d’un ou plusieurs liens du réseau, tout en minimisant le coût de dimensionnement du réseau. Nos contributions principales sont la proposition de deux stratégies de protection/routage nommée Flow Thinning et Elastic Flow Rerouting. La thèse est organisée en trois parties. Dans la première partie, nous présentons la problématique de la thèse avant de passer en revue les stratégies de protection et reroutage de la littérature, leur modélisation et méthode de résolution. La deuxième partie présente en détails la première stratégie de protection appelée Flow-Thinning. Cette stratégie gère les pannes partielles en diminuant la bande passante de certain flots qui passent par le ou les arc(s) perturbés. Cela implique un surdimensionnement du routage nominal permettant d’assurer le trafic en cas de perturbations. La troisième et dernière partie concerne la deuxième stratégie de routage dénommée Elastic Flow Rerouting. Cette stratégie est un peu plus complexe que la première dans le sens où, en cas de panne, une distinction est faite entre les demandes perturbées ou non. Si une demande est perturbée, elle peu augmenter le trafic sur ces chemins. Si elle ne l’est pas, elle peut libérer de la bande passante sous la condition qu’elle ne devienne pas perturbée à son tour. Notons que ces deux stratégies sont assez difficiles du point de vue de leur complexité. Cette thèse a fait l’objet de divers travaux écrits : trois articles (acceptés ou en révision) dans des journaux (Fouquet et al. (2015b), Pióro et al. (2015), Shinko et al. (2015)), deux articles invités (Fouquet and Nace (2015), Fouquet et al. (2014c)) et huit articles dans des conférences internationales (Fouquet et al. (2015a; 2014d;a;b;e), Pióro et al. (2013b;a), Shinko et al. (2013)). Notons que Pióro et al. (2013b) a reçu le "Best Paper Award" de la conférence RNDM 2013. Pour finir, notons que cette thèse a été réalisée au laboratoire Heudiasyc de l’Université de Technologie de Compiègne (UTC). Elle a été financée par le Ministère de l’enseignement et de la recherche français3 avec le soutien du labex MS2T4 de l’UTC
This thesis summaries the work we have done in optimization of resilient communication networks. More specifically, the main goal is to propose appropriated recovery mechanisms for managing the demand traffic in a network under partial failures, i.e. when some part of the network (one or some links and/or nodes) is operational with reduced capacity. The main criterion in deciding the efficiency of the proposed recovery scheme is the dimensioning cost of the network while keeping the management cost at reasonable levels. Our main contribution is the design of two restoration strategies named Flow Thinning and Elastic Flow Rerouting. This document is organized in three main parts. In the first part, we present the problematic of the thesis. It includes an introduction on the protection and rerouting state-of-art strategies, together with their mathematical models and resolution methods. The second part presents in depth the first protection strategy named Flow Thinning. This strategy manages partial failures by decreasing appropriately the bandwidth on some flows routed through one of perturbed links. This implies overdimensionning of the network in the nominal state to ensure demand traffic in all failure states. The third and last part deals with the second rerouting strategy called Elastic Flow Rerouting. This strategy is a bit more complex than the first one because, in a failure state, we need to distinguish demands which are disturbed and the one which are not. If a demand is disturbed, it can increase the traffic on some of its paths. If it is not disturbed, it can release bandwidth on paths at the condition it remains non-disturbed. All this allows for further reducing the dimensioning cost but at a higher cost in terms of recovery process management. Note that the dimensioning problems for each strategy are shown to be NP-hard in their general form. The work of the thesis has been published in: three journal articles (Fouquet et al. (2015b), Pióro et al. (2015), Shinko et al. (2015)), two invited articles (Fouquet and Nace (2015), Fouquet et al. (2014c)) and height articles in international conferences (Fouquet et al. (2015a; 2014d;a;b;e), Pióro et al. (2013b;a), Shinko et al. (2013)). Note that Pióro et al. (2013b) has been rewarded by a "Best Paper Award" from the RNDM conference. To conclude, note that this thesis was realized in the Heudiasyc laboratory, from the Université de Technologie de Compiègne (UTC). It was financed by the French Ministry of Higher Education and Research1 with the support of the Labex MS2T2 of the UTC

Dernièrement une technique de désalinisation à base de carbone poreux, qui constitue une avancée importante parmi les nombreuses technologies de désalinisation de l'eau, a été rapportée. Le principe repose sur le fait que les ions Na+ et Cl- sont adsorbés dans les pores des carbones sous l'effet d'une polarisation externe : les ions sodium sont adsorbés à l'électrode négative et les chlorures à la positive. Notre travail porte sur le développement des matériaux et sur le design des cellules optimisées, l'objectif étant d'améliorer le rendement énergétique du procédé de désalinisation. Dans ce contexte nous étudions aussi le concept de EFC (Electrochemical Flow Capacitor) qui consiste à faire circuler une suspension de carbone dans l'eau salée à l'intérieur d'une cellule électrochimique. Nous avons étudié dans un premier temps les différents composants de la cellule électrochimique, des interactions solvant/soluté jusqu'à la structure des carbones utilisés comme matériaux d'électrode. Ces études se sont faites en utilisant un montage classique de supercondensateur, c'est-à-dire une cellule dans laquelle les deux électrodes de carbone poreux (anode et cathode) sont mise en œuvre sous forme de film qui recouvre un colleteur de courant. Nous avons caractérisé une cellule de désalinisation en utilisant différents types d'électrodes et le couple redox [FeIII(CN)6]3- / [FeII(CN)6]4- comme sonde électrochimique. Notre approche a permis de définir un nombre sans dimension teta, qui est proportionnel au débit et inversement proportionnel à la vitesse de balayage du potentiel, donnant une ligne directrice pour définir les différents régimes de fonctionnement pour la cellule en mode flow. Deux régimes de fonctionnement ont été mis en évidence : un régime permanent pour teta> 45, permettant une adsorption de charge plus élevée et efficace, et un domaine non permanent pour teta <45. Enfin nous avons procédé à la formulation des suspensions de carbone. Nous avons étudié dans ce sens la rhéologie et les propriétés électrochimiques des suspensions en fonction de la composition, pour afin déterminer la meilleure composition de suspension à utiliser pour notre cellule fonctionnant en mode EFC
Recently, a desalination technique based on porous carbon has been reported, merging together desalination process with electrochemical energy storage. Thanks to this new strategy, an important step forward, respect to other water desalination technologies, has been achieved. The principle is based on the capacitive adsorption of Na+ and Cl- ions in the pores of a porous activated carbon, constituting the active material of an electrochemical double layer capacitor electrode. Differently from conventional EDLC, the active material is made in the present case as slurries flowed through an electrochemical cell to achieve a continuous desalination of seat water; such system has been named Electrochemical Flow Capacitor (ELC). We first studied the different components of the electrochemical cell, from solvent / solute interactions to the structure of the carbons used as electrode materials. These studies were done using a conventional supercapacitor assembly, i.e. a cell in which the two porous carbon electrodes (anode and cathode) are implemented as a film. We characterized a desalinization cell using different type of electrodes using the [FeIII(CN)6]3- / [FeII(CN)6]4- redox couple as an electrochemical probe. Our approach allowed to define a dimensionless number teta, which is proportional to the flow rate and inversely proportional to the potential scan rate, giving a guideline to sort out different operating regimes in the flow cell. Two operating regimes have been evidenced: a permanent regime for teta > 45, allowing for higher and efficient charge adsorption, and a non-permanent domain for teta < 45. Finally, we proceeded to the formulation of carbon suspensions. We studied the rheology and the electrochemical properties of the suspensions according to the composition in order to determine the best suspension composition to use for our cell operating in EFC mode

Orientador: Luiz Felipe Mendes de Moura
Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Mecânica
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Resumo: Este trabalho tem como objetivo a simulação numérica de um sensor de tomografia capacitiva elétrica, em função da permissividade elétrica relativa das fases presentes dentro da tubulação, com a finalidade de determinar a melhor geometria do sensor para a geração de imagem de escoamentos numa mistura bifásica ar-água, levando em consideração fluidos com efeito da condutividade nula. A simulação numérica do sensor de tomografia capacitiva é de crucial importância para o desenvolvimento de um tomógrafo capacitivo usado em aplicações específicas, como é o caso do monitoramento de escoamentos bifásicos. A tomografia capacitiva elétrica é uma tecnologia recente que vem se desenvolvendo desde o início de 1980, quando começou a ser utilizada para análise de processos industriais, principalmente em escoamentos multifásicos. Ela é utilizada para gerar uma imagem do interior da tubulação de acordo com a permissividade relativa das fases ali presentes, sendo atualmente o tipo de tomografia de processos mais utilizada. Após a determinação de algumas premissas do projeto como, o diâmetro da tubulação que foi simulada na horizontal, o comprimento dos eletrodos que seriam montados do lado externo da tubulação, as simulações bidimensionais foram realizadas para se obter o melhor espaçamento entre os doze eletrodos do sensor e a distância ideal da blindagem externa. Com as simulações tridimensionais, foi investigada a necessidade de utilização dos eletrodos de guarda, assim como, foi realizada a simulação da geometria final do sensor numa mudança dos componentes de ar para água no interior da tubulação. Os resultados obtidos neste trabalho permitiram determinar a geometria mais adequada do sensor para a situação proposta, assim como, obter o valor das capacitâncias para diferentes condições de escoamento. Os resultados das simulações tridimensionais apontaram as principais limitações de uma análise bidimensional
Abstract: This study was aimed to realize numerical simulations of a capacitive electrical tomography sensor, depending on the relative permittivity of the phases inside the pipe, in order to determine the best geometry of the sensor to generate the image of the flow in the air-water two-phase flow, taking into account the effect of conductivity zero in the fluids. Numerical simulation of the ECT sensor is of crucial importance to develop a capacitive tomograph used in specific applications such as monitoring biphasic flow. Electrical capacitance tomography is a new technology that has been developed since early 1980, when it began to be used in industrial processes, mainly in multiphase flows. It is used to generate an image from inside the pipe according to the relative permittivity of the phases present there, and is currently the type of process tomography procedures most commonly used. After the determination of some assumptions of the project as the diameter of the pipe that was simulated in the horizontal, the length of the electrodes that must be assembled outside the pipe, the two-dimensional simulations were performed to obtain the best spacing between the twelve electrodes of the sensor and the ideal distance of the outer shield. With the three-dimensional simulations, we investigated the necessity of use guard electrodes, as well as, it was realized the simulation of the final geometry of the sensor components in a change of air to water inside the pipe. The results of this study allow us to determine the most suitable sensor geometry for the proposed situation, as well as obtaining the value of capacitance for different flow conditions. The results of three-dimensional simulations showed the main limitations of a two dimensional analysis
Mestrado
Termica e Fluidos
Mestre em Engenharia Mecânica

CAPES
Além de estarem presentes na natureza, os escoamentos bifásicos possuem ampla aplicação industrial, sendo encontrados nas áreas química, nuclear, de geração de energia, petrolífera e espacial, onde escoamentos do tipo gás-líquido são os mais comuns. Eles são caracterizados pelo fluxo de duas substâncias imiscíveis, denominadas fases, em um sistema. A caracterização e o estudo destes escoamentos são importantes tanto na realização de projetos, quanto no monitoramento e controle de plantas aonde eles ocorrem. Um dos parâmetros utilizados na caracterização é a fração de vazio, que indica a proporção de gás em escoamentos gás liquido. As fases de um escoamento possuem diferentes propriedades elétricas, como condutividade e permissividade. Dessa forma, caso placas condutoras sejam dispostas ao redor de uma tubulação, pode ser formado um capacitor cuja capacitância dependa das características da mistura que escoa. O objetivo desta dissertação é o desenvolvimento de um sensor capacitivo não invasivo para determinação de fração de vazio em escoamentos bifásicos. Este trabalho apresenta a montagem dos eletrodos, o desenvolvimento de um hardware para detecção de variações na capacitância dos eletrodos e o desenvolvimento de um software para leitura das medições do hardware. A resposta do sensor desenvolvido não depende apenas da proporção volumétrica das fases em seu interior, mas também do padrão de escoamento, ou seja, da forma como elas estão distribuídas. Devido a isso, a resposta do sensor foi avaliada para diversos padrões de escoamento através de simulações do campo elétrico pelo método dos elementos finitos. Com base nos resultados das simulações e nas medidas da eletrônica desenvolvida, valores de fração de vazio foram obtidos para escoamentos ar água em bancadas de teste. Resultados obtidos mostram o bom desempenho do sistema capacitivo desenvolvido, o qual pode ser aplicado em estudos aprofundados do escoamento bifásico.
Two-phase flows are not only present in environmental phenomena such as clouds, but are found widespread in industrial applications. Such flows may be described as the stream of two immiscible substances, called phases, in a pipe or vessel. Most usual type of flow is gas-liquid flow and it can be found in chemical, nuclear, power generation, petroleum, and space industry. The study and characterization of such flows are important both in the realization of projects as in the monitoring and control of the facilities in which they occur. An important parameter in flow characterization is the void fraction, which indicates the volumetric amount of gas in gas-liquid flows. The gaseous and liquid phases in a flow usually present different electric properties, such as conductivity and permittivity. If electrodes are arranged around a pipe, they may form a capacitor whose capacitance depend upon the flowing mixture properties and their spatial distribution. The main goal of this work is to develop a non-invasive capacitive probe for void fraction determination in two-phase flow. It describes the assembly of the electrodes, the development of hardware for capacitance measurement, and the development of software that provides access to the measurement data obtained by the hardware. The response of capacitive sensors depends not only on void fraction values, but also on the flow pattern, that is, on the way that phases are distributed inside the pipe. Due to this fact, electric field simulations of the sensor’s response at different flow patterns were performed. Based on the results of the simulations and on the measurement results, void fraction values for air-water flow at controlled conditions was calculated and comparatively evaluated. The results obtained show the good performance of developed capacitive probe which may now be deployed in two-phase flow studies.

My diploma thesis deals with the issue revitalization of a small stream. Assessment and design of revitalization is done on Kuřimka stream which flows through the cadastral territory of the Moravian Knínice - Chudčice - Kníničky. In the diploma thesis were designed several of revitalization measures: stabilization of longitudinal tilt with the use of stone steps in the bottom and wooden thresholds, sedimentation reservoir for capturing sediment and slope stabilization using willow fences and gabions. Proposal of revitalization measures does not deteriorate runoff conditions.

The global photovoltaic (PV) market is growing, contributing to reduced climate emissions from electricity production. Historically, PV deployment mainly occurred in developed and electrified countries with a high level of certainty over their electrical system. Recently, this trend has started to change, contributing to a more globally distributed PV market. In primarily two of the emerging markets, Africa and the Middle East, the statistical situation is weak or non-existent, making it hard to monitor and track the PV development. PV devices can be grid-connected or off-grid, installed in PV parks or in smaller household applications, which further complicates the monitoring. As a result, the best available statistics on these markets, provided by the International Renewable Energy Agency (IRENA), are to a major part based on estimations not built on any official data.  In a pilot study a instrument prototype, Njord, for converting monetary trade data of PV devices into installed PV capacities was initiated, with the aim to provide more accurate estimates for these markets. Njord is in this study further developed, by increasing its resolution and adjusting assumptions. Further, an additional conversion factor, namely PV module weight, is implemented to improve the accuracy of the predictions. The time frame of Njord is enlarged enabling estimates of accumulated capacities, in contrast to previously only annual installations. The instrument methodology is based on a bottom-up approach of processing import and export customs data, and converting the data to installed capacities using the price and weight of a PV module per wattage. In addition to the further development of Njord, the trade data is used to map and analyse monetary trade flows and thereby market values. Identified improvements concerned, among others, to adjust the percentage of PV modules in the customs code for countries without specific codes, and to fill data gaps with additional mirror data. The weight conversion factor was initially implemented as a parallel instrument to the price based. The two conversion factors were then combined into an instrument choosing the most suitable conversion factor with regards to a number of constraints. The instrument performance was validated against reference countries with well documented PV markets, qualitatively customs data, and small domestic PV manufacturing. For the reference countries and the comparative period of 2016 – 2018, the total deviations were improved from spanning 11.1 % – 17.0 % to 0.5 – 22.6 %. The best performance is seen for the most recent years of 2018 and 2019, with total deviations of 0.5 % and 4.1 % respectively. Njord shows high performance for estimating accumulated capacity, with a deviation of 4.3 % in the end of 2019. When applying Njord to the markets of interest, Africa and the Middle East, the results are significantly higher than the IRENA estimates, with a result of 118 % higher for Africa and 127 % higher for the Middle East. This indicates that the PV deployment in these emerging markets could be underestimated in today's statistical situation.  In combination with the instrument results, mapping trade flows has shown to give comprehensive information about the PV markets of interest and shows the potential of using trade data for this type of analysis. China distinguishes as the dominant trade partner for both Africa and the Middle East, in line with the global PV market. Although these markets are small relative the global PV context, there was in 2019 still a net import of PV modules of in total 879 million US$ for Africa and 728 million US$ for the Middle East, and the markets are growing fast. Further, mapping trade flows has shown to identify manufacturing countries on the markets of interest, which there also is a lack of information on. The trade patterns and its inherent monetary values could be used to for example identify market development and business opportunities.

Em eletroforese capilar, a reprodutibilidade depende essencialmente da manutenção do sinal e no tempo de migração das espécies. A alteração do fluxo eletrosmótico (EOF) entre corridas é um dos principais fatores que afetam esses parâmetros. Nesse trabalho, é proposto um sistema de monitoramento do EOF baseado em marcas térmicas (TMs), que consistem em sinais presentes em um eletroferograma devido a uma perturbação do eletrólito de corrida ocasionada por um breve aquecimento (da ordem de 100 ms) de uma pequena porção do capilar (aproximadamente 1 mm), sob ação do campo elétrico. O dispositivo responsável pelo aquecimento que se mostrou mais eficiente consistiu em um resistor SMD de 15 Ω sobre o qual 5 V eram aplicados para gerar aquecimento. Estudos sobre a origem das TMs sugerem que o fenômeno está relacionado às mudanças do número de transporte das espécies devido à variação de temperatura. Essas conclusões foram baseadas na comparação do perfil dos sinais de TM com valores de número de transporte, além de estudos envolvendo simulação computacional. Diversas aplicações para as marcas térmicas foram propostas: correção de variação de tempo de migração devido a alterações do EOF, medida direta do EOF e para otimização de parâmetros do detector condutométrico sem contato. As TMs revelaram-se, então, um sistema prático e de fácil implementação, que pode ser utilizado como uma espécie de padrão interno. Adicionalmente, o emprego das TMs em um novo sistema de injeção de amostra, chamado de injeção térmica, foi também proposto. A vantagem desse tipo de injeção consiste na minimização de problemas de contínua introdução de amostra no canal de separação em microchip-CE. Para realizar essa injeção, o capilar é preenchido com a amostra diluída em um eletrólito de corrida e a injeção ocorre quando uma TM é gerada. Estudos com soluções de NaCl apresentaram faixa de resposta linear entre 10 µmol L-1 e 1 mmol L-1 para sódio. Entretanto, problemas de interferência sobre a sensibilidade e a mobilidade dos analitos foram obstáculos enfrentados. Também foi alvo de estudo o emprego da injeção térmica em uma técnica de multiplexação para aumento de relação sinal/ruído, baseado em um novo algoritmo. Embora o modelamento matemático tenha sido eficiente para decodificação de sinais, não foi possível obter o aumento na relação sinal/ruído almejado, pois o tempo de análise seria excessivamente longo. No entanto, a utilização da injeção térmica nesse tipo de estratégia mostrou-se bastante adequada, pois ela requer que diversas injeções sejam realizadas sequencialmente sem a interrupção do potencial de corrida, característica que esse sistema de injeção permite. Posteriormente, a implementação de estratégias que gerassem TMs em tempos mais curtos poderiam viabilizar a técnica. Finalmente, a utilização de TMs como ferramenta para obtenção de constantes físico-químicas, como pKa e mobilidade por exemplo, utilizando a eletroforese capilar mostra-se como uma grande perspectiva para a técnica
In capillary electrophoresis, reproducibility depends essentially on the maintenance of the signal and the migration time when the analysis of the same sample is repeated. Variations in the electroosmotic flow (EOF) between runs are one of the major factors affecting these parameters. In this work, a new approach to monitor the EOF based on thermal marks (TMs) is proposed. TM consists in a signal present in the electropherogram caused by heating (typically 100 ms) a small portion of the capillary (approximately 1 mm), while the electric field is applied. The most effective device to promote the heating was a 15-Ω SMD resistor, powered at 5 V. Studies about the origin of TMs suggest that the phenomenon is related to variations in the transport number of the species due to alterations in the temperature. This conclusion was based on comparison between the TM profile and the transport numbers values, as well as results from computer simulation. The proposed applications for TM include: correction in variations of migration times with alterations on EOF, EOF measurement and optimization of the parameters of contactless conductivity detection. Additionally, a new sample injection procedure, called thermal injection, was also proposed. The advantage of this injection consists in minimization of leakage problems related to the continuous introduction of the sample in the separation channel in microchip-CE. To perform the thermal injection, the capillary is completely filled with the sample diluted in a BGE and the injection occurs with the generation of a TM. Studies with NaCl solutions presented extensive linear response range from 10 µmol L-1 to 1 mmol L-1. However, interference problems on sensibility and analytes mobilities appeared. The use of low-concentration solutions diminishes these problems. However, the analytical signal is also diminished, needing a strategy to raise the sensitivity. Thus, a multiplexing technique based on a new algorithm was also introduced in order to improve signal-to-noise ratio. Although the efficiency of the mathematic modeling on the signals decoding, the desired improvement of signal/noise ratio was not obtained, because the analysis time would be excessively high. However, the employment of the thermal injection seems to be very suitable for multiplexing, due to the possibility of performing several sequential injections with no interruption of the electric field. Afterwards, the implementation of fast velocity devices to generate TMs would enable the technique. Finally, the great perspective to applications of TM concerns in the use of TMs to obtain physical chemical constants, such as pKa and ionic mobilities. The present work describes values of ionic mobilities calculated to monopropyl carbonate, monoisopropyl carbonate, and hydronium.

Cette thèse étudie d'abord l'interaction entre un lit de grains et un écoulement de Couette visqueux oscillant. Le nombre de Shields est d'ordre 1 et le Reynolds de grain petit devant 1. L'injection d'un colorant met en évidence un écoulement moyen uniforme orienté des creux vers les crêtes des rides. Le calcul théorique incluant la déformation lagrangienne du colorant retrouve ces résultats. La croissance des rides est étudiée. La longueur d'onde initiale est indépendante du nombre de Shields. Un temps de latence existe avant croissance et correspond à une compaction du lit. La croissance s'accompagne elle d'une décompaction qui semble localisée aux crêtes. L'étude du mouvement des grains montre un lien étroit avec l'évolution microscopique: vitesses, densité des grains mobiles. Une partie indépendante traite de l'effondrement d'une colonne de grains secs. Un modèle Saint-Venant avec ajout de masse permet de reproduire numériquement les lois d'échelle expérimentales (distance et hauteur)
The interaction between a granular bed and a viscous oscillating Couette flow is studied. The Shields number is close to 1 and the particle Reynolds number small relative to 1. The injection an ink streak above the ripples shows the existence of a steady streaming directed from troughs to crests. Theoretical calculations including lagrangian deformation of the streak recover the experimental results. Growth of the ripples is then studied. The initial wavelength seems independent of Shields number and is quite scattered. A latency period exists before the onset of instability, during which bed compaction is observed, whereas decompaction occurs during ripple growth. Macroscopic and grain-size behaviours are strongly related. Decompaction seems localised on ripples'crests. An independant part deals with the collapse of a dry granular column. A shallow-water model combined with progressive mass addition enables to reproduce numerically experimental scaling laws for runout distance and height

碩士
國立清華大學
電子工程研究所
102
The research studies a capacitive micro-sensor used for long-term respiratory monitoring of patients with breathing difficulties. By using CMOS-MEMS technology, we can integrate sensing structures and circuits into one chip. Parasitic effect is therefore reduced to enhance the signal-to-noise ratio. The chip size and fabrication cost are reduced as well. The capacitive flow sensor is fabricated by using the TSMC 0.35-μm 2P4M (two-polysilicon-four-metal) CMOS process. The differential sensing capacitances are formed by the metallization and polysilicon layers. Capacitance change is produced by momentum change of the air flow on the microstructure, which is released by wet-etching of metal-1 and metal-3. The sensor area is 320μm × 230μm. The sensing capacitances are about 124 fF. The total chip area is 2.46 × 2.46 mm^2. The sensing circuit is operated at 5 V with a total current consumption of 5 mA. The measured data shows the sensor has a sensitivity of 3.33 mV/(L⁄min) and a detection limit of 34.4 (mL/min) within a 1-Hz bandwidth. We have successfully measured the waveform from a subject’s nasal respiration.

碩士
國立臺灣大學
電子工程學研究所
100
In this research, we try to develop a capacitive tactile sensor for non-invasive blood flow monitoring. The capacitance variation of the capacitive tactile sensor was measured with the membrane deflection by an external pressure. This capacitive sensor is realized by using the CMOS-MEMS fabrication process which is based on TSMC 0.35μm 2P4M (2 polycrystalline silicon and 4 metal) process and self-developed post process. Two metal sacrificial layers of M1 and M3 are etched so the sensing electrodes of other two metal layers of M2, M4, and one polycrystalline silicon layer were formed. Two sensing capacitors consisting of three parallel sensing electrodes were connected vertically. The sensitivity of the sensor can be enhanced by a specific configuration of two sensing capacitors. Two different structure designs were proposed to cope with different sensing ranges. The detection range of L-type design is from 0 to 50 mmHg while the Square-type design is from 0 to 200 mmHg. The capacitance variation was recorded via an oscillator circuit converting a capacitance change into a frequency change. The maximum sensitivity of two designs are 0.1723 Hz/mmHg and 0.588 Hz/mmHg.

In this thesis, two different experimental approaches to capacitive deionization (CDI) process are presented. In the first approach, transient system characteristics were analyzed to find three different operating points, first based on minimum outlet concentration, second based on maximum average adsorption rate and third based on maximum adsorption efficiency. These three operating points were compared in long term desalination tests. In addition, the effects of inlet stream salinity and CDI system size have been characterized to assess the feasibility of a commercial CDI system operating at brackish water salinity levels. In the second approach, the physical phenomena occurring inside a capacitive deionization system were studied by laser-induced fluorescence visualization of a “pseudo-porous” CDI microstructure. A model CDI cell was fabricated on a silicon-on-insulator (SOI) substrate and charged fluorophores were used to visualize the simultaneous electro migration of oppositely charged ions and to obtain in situ concentration measurements.
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碩士
國立交通大學
環境工程系所
105
Capacitive deionization (CDI) technology is the use of an external voltage for generation of electrode capacitance, thereby removing ions from the aqueous solution. Carbon material applied in the CDI technology include activated carbon, mesoporous carbon material and carbon nanotubes, which store charge with the mechanism of electrical double layer capacitance. Activated carbon processes a very high specific surface area, however, due to poor conductivity of activated carbon, carbon black can be then incorporated therein to improve the overall specific capacitance. Therefore, incorporate different proportions of carbon black in the activated carbon was conducted to prepare capacitive deionization electrode. With those electrodes, the specific capacitance and electrosorption capacity for the activated carbon with different proportions of carbon black could be compared, and screened out a best performance electrode. A Flow-through modular with this preferred electrode was then applied to evaluate its performance on the desalination of NaCl solution. This study can be divided into two parts, the first part is to realize the relationship between the specific capacitance and the desalting amount. Activated carbon (AC) were mixed with carbon black (CB) by using a polymer binder (PVdF), and then landed on the titanium mesh via dip coating method. The mesh AC electrodes with different the ratio of CB were prepared and their changes in the specific capacitance as well as electrically adsorption capacity were investigated. The second part is flow-through modules were operated at different voltages and flow rates for the evaluation of their performances. The results showed that 10% PVdF performed the best coating. With the increase of carbon black, the specific capacitance of CDI electrode has indeed improved due to pseudocapacitance contributed by oxygen-containg functional groups (C=O). The results also showed that flow-through type of CDI modules assembly with 10% of CB laden AC mesh electrode performs the best desalination capacity, especially at the operating voltage of 1.2 V and the flow rate of 20 ml/min.

Dimitris Bertsimas, Sarah Stock.
Includes bibliographical references (p. 41-42).
Research supported by grants from Draper Laboratory and the FAA. Research supported by a Presidential Young Investigator Award. DDM-9158118