Thesis (MEng) -- Stellenbosch University, 2014. / ENGLISH ABSTRACT: This project investigates aspects of a novel inherently safe nuclear power steam supply system as safety is of paramount importance. The system envisaged has unique features namely: a) a two-phase flow flash-tube type natural circulating primary loop (also the secondary radioactive particle containment); b) a twophase flow thermosyphon heat pipe type heat exchanger secondary loop is used to transfer heat from the primary loop to the steam generators, thereby physically separating the two flow streams from one another; c) a natural convection air cooled condenser for the removal of the reactor’s residual heat; d) a unique core using TRISO type fuel (acting as the primary radioactive particle containment) with life of at least 8.9 years; e) a steel containment vessel acting as a tertiary radioactive product containment; f) a concrete containing structure with air vents to allow air to pass over the main steel containment vessel for cooling purposes in the case of an emergency, and for the removal of parasitic heat during operation. In particular the primary and secondary loops of the proposed system are investigated. This is done by design, construction and testing of a small scale experimental set-up of the primary and secondary loops as well as the development of theoretical models for the two loops. A literature survey focusing on nuclear technology, thermosyphon loops, natural circulating loop instabilities, heat pipes, and two-phase flow modelling is presented to give a brief overview of the technologies as well as tools used in the work undertaken. Observations of the inside flow behaviour of the primary loop experimental set-up were made possible by windows providing many insights into the inner workings, such as plume formation and geysering. The transient response of the secondary heat pipe loop start-up is also investigated. A thermal resistance theoretical model was developed for the secondary loop using heat transfer formulae from theory as well as experimentally semiempirical correlated formula. Different states of operation of the secondary loop were observed during testing with the theoretical model of the condensing regime correlating well, two-phase regime correlating acceptably and liquid regime correlating poorly to experimental results and thus were modelled using an experimentally determined overall heat transfer coefficient. The secondary loop model of the liquid regime is coupled with the primary loop theoretical model to predict the system’s performance. A homogeneous, one-dimensional, simple theoretical model for the primary loop was derived and computer simulated. The results did not compare well with experimental results for single phase flow and failed to capture the onset of two-phase flow. The assumptions of one dimensional model with a unidirectional flow, a hydrostatic pressure problem, a constant volumetric flow rate and the inability of the implementation of the code to handle expansion are noted as some of the flaws in the theoretical model. The following recommendations are made: a more advanced design of the pressuriser should be incorporated into the experiment; the secondary loop’s theoretical model should be characterised under a broader set of operating conditions; the computer program can be used as the basis for further research and implementation of alternative solution algorithms and models. / AFRIKKANSE OPSOMMING: Hierdie projek ondersoek aspekte van ’n ongewone, essensieel veilige kernkrag stoomtoevoer-stelsel, omdat veiligheid van kardinale belang is. Die stelsel wat voorgestel is, het unieke eienskappe, naamlik: a) ’n twee-fasevloei flits-buistipe natuurlik sirkulerende primêre lus (wat ook die sekondêre inperking van radioaktiewe materiaal bevat); b) ’n twee-fasevloei termo-heweleffek sekondêre lus hitte-pyp hitte-uitruiler word gebruik om die hitte vanaf die primêre lus oor te dra na die stoomkragopwekkers en daardeur word die twee strome se vloei fisies geskei van mekaar; c) ’n natuurlike konveksie lugverkoelde kondensor word gebruik vir die verwydering van die reaktors se oortollige hitte; d) ’n unieke kern gebruik TRISO-tipe brandstof (wat as die primêre inperking van radioaktiewe materiaal optree) met ’n lewe van minstens 8.9 jaar; e) ’n inperkingshouer van staal wat optree as ’n tersiêre radioaktiewe produkhouer; f) ’n betonstruktuur met lugventilasie om toe te laat dat lug oor die hoof staalhouer vloei vir verkoeling in ’n noodgeval, en vir die verwydering van parasitiese hitte tydens werking. Hoofsaaklik word die primêre en sekondêre lusse van die voorgestelde stelsel ondersoek. Dit word gedoen deur die ontwerp, konstruksie en die toets van ’n eksperimentele opstelling van die primêre en sekondêre lusse op klein skaal, sowel as die ontwikkeling van teoretiese modelle vir die twee lusse. ’n Literatuurstudie wat fokus op kerntegnologie, termo-heweleffeklusse, natuurlik sirkulerende lus instabiliteit, hitte-pype, en twee-fase vloeimodellering word aangebied om ’n kort oorsig te gee van die tegnologie, sowel as gereedskap gebruik in die werk wat onderneem is. Om die interne vloeigedrag van die primêre lus se eksperimentele opstelling waar te neem, word daar gebruik gemaak van vensters wat dien as ’n manier om die innerlike werking van die proses soos pluimvorming en die kook van die water in die warmwaterkolom te toon. Die oorgangsreaksie van die sekondêre hittepyplus aanvangs is ook ondersoek. ’n Teoretiese termiese weerstandmodel is ontwikkel vir die sekondêre lus met behulp van hitte-oordragformules waarvoor hitte-oordragteorie gebruik is, wat met eksperimentele semi-empiriese formules gekorreleer is. Verskillende toestande van die sekondêre lus se werking is waargeneem gedurende die toetse. Die teoretiese model het goed met die kondensasiestaat gekorreleer, terwyl by die twee-fasewerkswyse aanvaarbare korrellasies aangetref is en die uiteindelike vloeitoestand swakker gekorrelleer het met eksperimentele resultate en dus gemodelleer is met behulp van die NTU-effektiwiteitsmetode. Die sekondêre lusmodel van die vloeistoftoestand is gekoppel met die primêre lus teoretiese model om die werking van die stelsels te voorspel. ’n Homogene een-dimensionele eenvoudige teoretiese model van die primêre lus is afgelei en ’n rekenaar simulasie is uitgevoer. Die resultate vergelyk nie goed met die eksperimentele resultate vir enkelfasevloei en kon nie die aanvang van twee-fasevloei beskryf nie. Die aannemings van ’n een-dimensionele model met eenrigting vloei, ’n hidrostatiese druk probleem, ’n konstant volumetries vloeitempo en die onvermoë van die implementering van die kode om uitbreiding te hanteer is bekend as ’n paar van die foute in die teoretiese model. Die volgende aanbevelings word gemaak: ’n meer gevorderde ontwerp van drukreëlaar moet in die eksperiment ingesluit word; die sekondêre lus se teoretiese model moet gekenmerk word onder ’n wyer stel bedryfsomstandighede, en die rekenaar program kan gebruik word as die basis vir verdere navorsing en die implementering van alternatiewe algoritmes en modelle.

Circuitos de convecção natural ou sistemas de circulação natural são empregados em diversas áreas da engenharia. Reatores nucleares refrigerados a água utilizam circuitos de circulação natural como método passivo de seguranca. Em situações críticas, sem qualquer controle externo, o sistema permanece em segurança por suas próprias características de funcionamento (intrinsecamente seguro). O trabalho proposto consiste em estudar numericamente o circuito de circulação natural de água, localizado no Instituto de Pesquisas Energéticas e Nucleares / Comissão Nacional de Energia Nuclear em São Paulo, por meio do uso de modelos matemáticos, objetivando determinar o padrão do escoamento em condições sem mudança de fase líquido-vapor. A comparação dos resultados de temperatura obtidos por cada um dos modelos de turbulência aos pontos instrumentados no circuito experimental, na condição transitória, revelou desvios significativos nas respostas do modelo de zero equação. Desvios intermediário foram observados nos modelos de transporte da viscosidade turbulenta (EVTE), k - ω, SST e SSG e resultados melhores foram vericados nos modelos k - ε e DES (com significativa superioridade do primeiro modelo). / Natural circulation loops apply to many engineering applications such as: water heating solar energy system (thermo-siphons), thermal management of electrical components (voltage converter), geothermal energy, nuclear reactors, etc. In pressurized water nuclear reactors, known as PWR\'s, the natural circulation loops are employed to ensure passive safety. In critical situations, the heat transfer will occur only by natural convection, without any external control or mechanical devices. This feature is desired and has been considered in modern nuclear reactor projects. This work consists of a numerical study of the natural circulation loop, located at the Instituto de Pesquisas Energeticas e Nucleares / Comissão Nacional de Energia Nuclear in São Paulo, Brazil, in order to establish the ow pattern in single phase conditions. The comparison of numerical results to experiments in transient condition revealed significant deviations for the Zero Equation turbulence model. Intermediate deviations for the Eddy Viscosity Turbulence Equation (EVTE), k - ω, SST e SSG models. And the best results are obtained by the k - ε e DES models (with better results for the k - ε model).

Circuitos de convecção natural ou sistemas de circulação natural são empregados em diversas áreas da engenharia. Reatores nucleares refrigerados a água utilizam circuitos de circulação natural como método passivo de seguranca. Em situações críticas, sem qualquer controle externo, o sistema permanece em segurança por suas próprias características de funcionamento (intrinsecamente seguro). O trabalho proposto consiste em estudar numericamente o circuito de circulação natural de água, localizado no Instituto de Pesquisas Energéticas e Nucleares / Comissão Nacional de Energia Nuclear em São Paulo, por meio do uso de modelos matemáticos, objetivando determinar o padrão do escoamento em condições sem mudança de fase líquido-vapor. A comparação dos resultados de temperatura obtidos por cada um dos modelos de turbulência aos pontos instrumentados no circuito experimental, na condição transitória, revelou desvios significativos nas respostas do modelo de zero equação. Desvios intermediário foram observados nos modelos de transporte da viscosidade turbulenta (EVTE), k - ω, SST e SSG e resultados melhores foram vericados nos modelos k - ε e DES (com significativa superioridade do primeiro modelo). / Natural circulation loops apply to many engineering applications such as: water heating solar energy system (thermo-siphons), thermal management of electrical components (voltage converter), geothermal energy, nuclear reactors, etc. In pressurized water nuclear reactors, known as PWR\'s, the natural circulation loops are employed to ensure passive safety. In critical situations, the heat transfer will occur only by natural convection, without any external control or mechanical devices. This feature is desired and has been considered in modern nuclear reactor projects. This work consists of a numerical study of the natural circulation loop, located at the Instituto de Pesquisas Energeticas e Nucleares / Comissão Nacional de Energia Nuclear in São Paulo, Brazil, in order to establish the ow pattern in single phase conditions. The comparison of numerical results to experiments in transient condition revealed significant deviations for the Zero Equation turbulence model. Intermediate deviations for the Eddy Viscosity Turbulence Equation (EVTE), k - ω, SST e SSG models. And the best results are obtained by the k - ε e DES models (with better results for the k - ε model).

A segurança de instalações nucleares é uma preocupação mundial que tem crescido, sobretudo, após o acidente nuclear de Fukushima. O estudo de acidentes em reatores nucleares de pesquisa tal como o Acidente de Perda de Refrigerante (APR), considerado por muitas vezes um acidente base de projeto, é importante para garantir a integridade da instalação. O APR pode levar ao descobrimento parcial ou total do núcleo do reator e, como condição de segurança, deve-se garantir que haja a remoção do calor de decaimento dos elementos combustíveis. Esse trabalho teve o objetivo de realizar experimentos de descobrimento parcial e total no Elemento Combustível Instrumentado (ECI), construído no Instituto de Pesquisas Energética e Nucleares (IPEN), a fim de estudar os possíveis APRs em reatores de pesquisa. Uma seção de testes, denominada STAR, foi projetada e construída para simular os APRs. O ECI foi irradiado no núcleo do reator IEA-R1 (IPEN) e inserido na STAR, que ficou totalmente imersa na piscina do reator. No ECI, foram instalados termopares para medição das temperaturas do revestimento e do fluido em várias posições axiais e radiais. Foram realizados experimentos para cinco níveis de descobrimento do ECI, um total e quatro parciais, em duas condições distintas de calor de decaimento. Na análise dos resultados, verificou-se que os casos de descobrimento total foram os mais críticos, ou seja, as temperaturas do revestimento foram as maiores quando comparadas com os casos de descobrimentos parciais. Adicionalmente, foi realizada a simulação numérica de dois experimentos com o código RELAP5, cujos resultados demonstraram ótima concordância com os dos níveis experimentais, e temperaturas maiores que as experimentais. As máximas temperaturas do revestimento alcançadas em todos os experimentos ficaram bem abaixo da temperatura de empolamento do combustível, que é de 500°C. Assim, a STAR provou ser um aparato experimental seguro e confiável para a realização de experimentos de perda de refrigerante. / The safety of nuclear facilities has been a growing global concern mainly after the Fukushima nuclear accident. Studies on nuclear research reactor accidents such as the Loss of Coolant Accident (LOCA), considered many times a design basis accident, are important for guaranteeing the integrity of the plant. A LOCA may lead to the partial or complete uncovering of the fuel assemblies and assured decay heat removal is a safety condition. This work aimed to perform partial and complete uncovering experiments in the Instrumented Fuel Assembly (IFA) designed at the Instituto de Pesquisas Energéticas e Nucleares (IPEN) in order to study possible LOCAs in research reactors. A test section for experimental simulation of Loss of Coolant Accident named STAR was designed and built. The IFA was irradiated in the IEA-R1 and installed in the STAR, which was totally immersed in the reactor pool. Thermocouples were installed in the IFA to measure the clad and fluid temperatures in several axial and radial positions. The experiments were carried out for five levels of uncovering of IFA, being one complete uncovering and four partial uncovering, in two different conditions of decay heat. In the results analysis was observed that the cases of complete uncovering of the IFA were the most critical ones, that is, those cases presented higher clad temperatures when compared with partial uncovering cases. Additionally, a numerical simulation of two experiments was carried out by using the RELAP 5 code. The numerical results showed an optimum agreement with the experimental levels results and greater than the experimental temperatures. The maximum clad temperatures reached in all experiments were quite below the fuel blister temperature, which is 500 °C. Therefore, the STAR has proven to be a safe and reliable experimental apparatus for conducting loss of coolant experiments.

A segurança de instalações nucleares é uma preocupação mundial que tem crescido, sobretudo, após o acidente nuclear de Fukushima. O estudo de acidentes em reatores nucleares de pesquisa tal como o Acidente de Perda de Refrigerante (APR), considerado por muitas vezes um acidente base de projeto, é importante para garantir a integridade da instalação. O APR pode levar ao descobrimento parcial ou total do núcleo do reator e, como condição de segurança, deve-se garantir que haja a remoção do calor de decaimento dos elementos combustíveis. Esse trabalho teve o objetivo de realizar experimentos de descobrimento parcial e total no Elemento Combustível Instrumentado (ECI), construído no Instituto de Pesquisas Energética e Nucleares (IPEN), a fim de estudar os possíveis APRs em reatores de pesquisa. Uma seção de testes, denominada STAR, foi projetada e construída para simular os APRs. O ECI foi irradiado no núcleo do reator IEA-R1 (IPEN) e inserido na STAR, que ficou totalmente imersa na piscina do reator. No ECI, foram instalados termopares para medição das temperaturas do revestimento e do fluido em várias posições axiais e radiais. Foram realizados experimentos para cinco níveis de descobrimento do ECI, um total e quatro parciais, em duas condições distintas de calor de decaimento. Na análise dos resultados, verificou-se que os casos de descobrimento total foram os mais críticos, ou seja, as temperaturas do revestimento foram as maiores quando comparadas com os casos de descobrimentos parciais. Adicionalmente, foi realizada a simulação numérica de dois experimentos com o código RELAP5, cujos resultados demonstraram ótima concordância com os dos níveis experimentais, e temperaturas maiores que as experimentais. As máximas temperaturas do revestimento alcançadas em todos os experimentos ficaram bem abaixo da temperatura de empolamento do combustível, que é de 500°C. Assim, a STAR provou ser um aparato experimental seguro e confiável para a realização de experimentos de perda de refrigerante. / The safety of nuclear facilities has been a growing global concern mainly after the Fukushima nuclear accident. Studies on nuclear research reactor accidents such as the Loss of Coolant Accident (LOCA), considered many times a design basis accident, are important for guaranteeing the integrity of the plant. A LOCA may lead to the partial or complete uncovering of the fuel assemblies and assured decay heat removal is a safety condition. This work aimed to perform partial and complete uncovering experiments in the Instrumented Fuel Assembly (IFA) designed at the Instituto de Pesquisas Energéticas e Nucleares (IPEN) in order to study possible LOCAs in research reactors. A test section for experimental simulation of Loss of Coolant Accident named STAR was designed and built. The IFA was irradiated in the IEA-R1 and installed in the STAR, which was totally immersed in the reactor pool. Thermocouples were installed in the IFA to measure the clad and fluid temperatures in several axial and radial positions. The experiments were carried out for five levels of uncovering of IFA, being one complete uncovering and four partial uncovering, in two different conditions of decay heat. In the results analysis was observed that the cases of complete uncovering of the IFA were the most critical ones, that is, those cases presented higher clad temperatures when compared with partial uncovering cases. Additionally, a numerical simulation of two experiments was carried out by using the RELAP 5 code. The numerical results showed an optimum agreement with the experimental levels results and greater than the experimental temperatures. The maximum clad temperatures reached in all experiments were quite below the fuel blister temperature, which is 500 °C. Therefore, the STAR has proven to be a safe and reliable experimental apparatus for conducting loss of coolant experiments.

Thesis (MScEng)--Stellenbosch University, 2012. / ENGLISH ABSTRACT: The focus of this project was on the potential application of waste heat recovery and utilisation (WHR&U) systems in pebble bed modular reactor (PBMR) technology. The background theory provided in the literature survey showed that WHR&U systems have attracted the attention of many researchers over the past two decades, as using waste heat improves the system overall efficiency, notwithstanding the cost of extra plant. PBMR waste heat streams were identified and investigated based on the amount of heat rejected to the environment. WHR&U systems require specially designed heat recovery equipment, and as such the used and/or spent PBMR fuel tanks were considered by the way of example. An appropriately scaled system was designed, built and tested, to demonstrate the functioning of such a cooling system. Two separate and independent cooling lines, using natural circulation flow in a particular form of heat pipes called thermosyphon loops were used to ensure that the fuel tank is cooled when the power conversion unit has to be switched off for maintenance, or if it fails. A theoretical model that simulates the heat transfer process in the as-designed WHR&U system was developed. It is a one-dimensional flow model assuming quasi-static and incompressible liquid and vapour flow. An experimental investigation of the WHR&U system was performed in order to validate the theoretical model results. The experimental results were then used to modify the theoretical heat transfer coefficients so that they simulate the experiments more accurately. Three energy conversion devices, the dual-function absorption cycle (DFAC), the organic Rankine cycle (ORC) and the Stirling engine (SE), were identified as suitable for transforming the recovered heat into a useful form, depending on the source temperatures from 60 ºC to 800 ºC. This project focuses on a free-piston SE with emphasis on the thermo-dynamic performance of a SE heat exchanger. It was found that a heat exchanger with a copper woven wire mesh configuration has a relatively large gas-to-metal and metal-to-liquid heat transfer area. Tube-in-shell heat exchanger configurations were tested, with the working fluid flowing in ten copper inner pipes, while a coolant flows through the shell tube. A lumped parameter model was used to describe the thermo-fluid dynamic behaviour of the SE heat exchanger. In order to validate the theoretical results, a uni-directional flow experimental investigation was performed. The theoretical model was adjusted so that it simulated the SE heat exchanger. It was found that after this correction the theoretical model accurately predicts the experiment. Finally, a dynamic analysis of the SE heat exchanger experimental set-up was undertaken to show that, although vibrating, the heat exchanger setup assembly was indeed acceptable from a vibrational and fatigue point of view. / AFRIKAANSE OPSOMMING: Die hoofoogmerk met hierdie projek was die moontlike aanwending van afvalhitteherwinningen- benutting-(WHR&U-) stelsels in modulêre-gruisbedreaktor-(PBMR-) tegnologie. Agtergrondteorie in die literatuurondersoek toon dat WHR&U-stelsels al menige navorser se belangstelling geprikkel het, hetsy vanweë die moontlike ekonomiese voordele wat dit inhou óf vir besoedelingsvoorkoming, bo-en-behalwe die koste van bykomende toerusting. Die PBMRafvalhittestrome is ondersoek en bepaal op grond van die hoeveelheid hitte wat dit na die omgewing vrystel. Om in die prosesbehoeftes van WHR&U-stelsels te voorsien, moet goed ontwerpte, doelgemaakte hitteherwinningstoerusting in ʼn verkoelings- en/of verhittingsproses gebruik word, dus is die PBMR as voorbeeld gebruik vir die konsep. ʼn Toepaslik geskaleerde WHR&U-stelsel is dus ontwerp, gebou en getoets om die geldigheid van die stelselontwerp te toon. Twee onafhanklike verkoelingslyne, wat van natuurlike konveksie gebruik maak, in die vorm van hitte-pype of termoheuwel lusse, was gebruik om te verseker dat verkoeling verskaf word wanneer die hoof lus breek of instandhouding nodig hê. ʼn Teoretiese model is ontwikkel wat die hitteoordragproses in die ontwerpte WHR&U-stelsel simuleer. Dié model was ʼn eendimensionele vloeimodel wat kwasistatiese en onsamedrukbare vloeistof- en dampvloei in die WHR&U-stelsel-lusse veronderstel. ʼn Eksperimentele ondersoek is op die WHR&U-stelsel uitgevoer ten einde die teoretiese model se resultate te bevestig. Die eksperimentele resultate was dus geneem om die teoretiese hitteoordragkoëffisiënte aan te pas sodat dit die eksperimente kon simuleer. Drie energieomsettingstoestelle, naamlik die dubbel funksie absorpsie siklus (DFAC), die organiese Rankine siklus (ORC) en die Stirling enjin (SE), is as geskikte toestelle uitgewys om die herwonne hitte op grond van brontemperature tussen 60 ºC en 800 ºC in ʼn bruikbare vorm om te sit. Hierdie tesis het op vryesuier-SE’s gekonsentreer, met klem op die hitteruiler. Meer bepaald is die termodinamiese werkverrigting van ʼn SE-hitteruiler ondersoek. Daar is bevind dat ʼn hitteruiler met ʼn geweefde koperdraadmaas-samestelling oor ʼn betreklik groot gas-totmetaal- en metaal-tot-vloeistof-oordragoppervlakte beskik. Die verhitter en verkoeler is in ʼn buis-in-mantel-vorm ontwerp, met die werksvloeistof wat deur tien koperbinnepype vloei en ʼn koelmiddel deur die mantelbuis. ʼn Saamgevoegde-parameter-model is gebruik om die termodinamiese gedrag van die SEhitteruiler te beskryf. Ten einde die teoretiese resultate te bevestig, is ʼn eenrigtingvloeiproefondersoek uitgevoer. Die teoretiese model is aangepas sodat dit die SE-hitteruiler kon simuleer. Ná die nodige verstellings is daar bevind dat die teoretiese model die proefneming akkuraat voorspel. Laastens was ʼn dinamiese ontleding van die SE-hitteruiler ook onderneem om te toon dat, hoewel dit vibreer, die hitteruiler proef samestel inderdaad veilig is.

Este trabalho desenvolveu um novo método para a detecção de contornos em imagens digitais que apresentam objetos de interesse muito próximos e que contêm complexidades associadas ao fundo da imagem como variação abrupta de intensidade e oscilação de iluminação. O método desenvolvido utiliza lógicafuzzy e desvio padrão da declividade (Desvio padrão da declividade fuzzy - FuzDec) para o processamento de imagens e detecção de contorno. A detecção de contornos é uma tarefa importante para estimar características de escoamento bifásico através da segmentação da imagem das bolhas para obtenção de parâmetros como a fração de vazio e diâmetro de bolhas. FuzDec foi aplicado em imagens de instabilidades de circulação natural adquiridas experimentalmente. A aquisição das imagens foi feita utilizando o Circuito de Circulação Natural (CCN) do Instituto de Pesquisas Energéticas e Nucleares (IPEN). Este circuito é completamente constituído de tubos de vidro, o que permite a visualização e imageamento do escoamento monofásico e bifásico nos ciclos de circulação natural sob baixa pressão.Os resultados mostraram que o detector proposto conseguiu melhorar a identificação do contorno eficientemente em comparação aos detectores de contorno clássicos, sem a necessidade de fazer uso de algoritmos de suavização e sem intervenção humana. / This work has developed a new method for digital image contour detection which can be successfully applied to images presenting objects of interest with high proximity and presenting complexities related with background abrupt intensity fluctuations. The developed method makes use of fuzzy logic and declivity standard deviation (Fuzzy Declivity Standard Deviation FuzDec) to image processing and contour detection. Contour detection is an important task to estimate two-phase flow features through bubble segmentation in order to obtain parameters as void fraction and bubble diameter. FuzDec was applied to natural circulation instability images which were experimentally acquired. Image acquisition was done at the Natural Circulation Circuit (CCN) of the Instituto de Pesquisas Energéticas e Nucleares (IPEN) in Brazil. This facility is all made up with glass tubes allowing easy visualization and imaging of one-phase and two-phase flow patterns during natural circulation cycles under low pressures. Results confirm that the proposed detector can improve contour identification when compared to classical contour detector algorithms, without using smoothing algorithms or human intervention.

A Agência Internacional de Energia Atômica (IAEA - \"International Atomic Energy Agency\") vem incentivando o desenvolvimento de sistemas passivos de refrigeração em plantas nucleares visando a simplificação e o incremento da confiabilidade em funções essenciais de segurança nos projetos de uma próxima geração de reatores nucleares refrigerados a água. O principal fundamento desses sistemas é o emprego da circulação natural como sistema de segurança aplicável em operações de desligamento do reator para manutenção ou na ocorrência de acidentes. A circulação natural é um fenômeno que surge em virtude do gradiente de temperatura em pontos diferentes do circuito de refrigeração. Em condições extremas de estabilidade têm-se o estabelecimento do escoamento bifásico gás/líquido podendo configurar-se segundo diferentes regimes. A fração de vazio é reconhecida como um dos parâmetros chave na predição da ocorrência de instabilidades do escoamento bifásico. Apresenta-se neste trabalho uma inovadora metodologia para estimativa da fração de vazio a partir de imagens digitais capturadas diretamente de circuitos experimentais que geram o escoamento bifásico. O método é baseado na aquisição de imagens, com controle da profundidade de campo, de uma seção do Circuito de Circulação Natural (CCN) presente no IPEN/CNEN-SP. A imagem é segmentada com base na inferência fuzzy de diferentes parâmetros de segmentação e ajustada ao foco utilizado na sua aquisição. Ela é varrida de um modo inédito e iterativo, utilizando máscaras de diferentes tamanhos integrando um conjunto de redes neurais com a Transformada Randomizada de Hough. Cada diferente tamanho de máscara é escolhido de acordo com os tamanhos das bolhas que são os objetos de interesse. O volume da bolha é estimado baseado em sua projeção plana capturada nas imagens digitais. O cálculo da fração de vazio considera o volume da seção geométrica do escoamento no tubo de vidro cilíndrico e a profundidade de campo utilizada e nos parâmetros geométricos inferidos para cada bolha detectada. Os resultados mostraram que a integração entre o conjunto de redes neurais e a Transformada Randomizada de Hough aumentaram a robustez das estimativas do sistema. / The International Atomic Energy Agency (IAEA) has been encouraging the use of passive cooling systems in new designs of nuclear power plants. Next nuclear reactor generations are intended to possess simpler and robust safety functions. Natural circulation based systems hold an undoubtedly prominent position among these. Natural circulation phenomenon occurrence depends only on the existence of refrigerant liquid temperature gradient in different sections of the plant refrigerator circuit. The study of limit conditions for these systems has led to instability behavior analysis where many different two-phase flow patterns are present. Void fraction is a key parameter in thermal transfer analysis of theses flow instability conditions. This works presents a new method to estimate void fraction from digital images captured at an experimental two-phase flow circuit. The method is primarily based on depth-of-field controlled image acquisition of a section of a closed loop of natural circulating water through cylindrical glass tubes. This loop is called Natural Circulation Facility (NCF) and is located at Nuclear and Engineering Research Institute in Brazil (IPEN/CNEN-SP). Image is segmented based on fuzzy inference of different segmentation parameters and adjusted to image acquisition focus. The image is then scanned in an inedited way using different-sized masks integrating a set of different artificial neural networks with a modified Randomized Hough Transform. Each different mask size is chosen in accordance to bubble sizes which are objects of interest. The bubble volume is estimated based on two-dimensional projection sizing based on digitally acquired images. Void fraction calculation takes into account the volume of the geometrical section of flow inside cylindrical glass tube considering used depth-of-field. It is also based on the summed bubble geometrical parameters inferred for each detected bubble. The results have shown that integration between artificial-neural-net sets and Randomized Hough Transforms increase system estimations robustness.

Este trabalho desenvolveu um novo método para a detecção de contornos em imagens digitais que apresentam objetos de interesse muito próximos e que contêm complexidades associadas ao fundo da imagem como variação abrupta de intensidade e oscilação de iluminação. O método desenvolvido utiliza lógicafuzzy e desvio padrão da declividade (Desvio padrão da declividade fuzzy - FuzDec) para o processamento de imagens e detecção de contorno. A detecção de contornos é uma tarefa importante para estimar características de escoamento bifásico através da segmentação da imagem das bolhas para obtenção de parâmetros como a fração de vazio e diâmetro de bolhas. FuzDec foi aplicado em imagens de instabilidades de circulação natural adquiridas experimentalmente. A aquisição das imagens foi feita utilizando o Circuito de Circulação Natural (CCN) do Instituto de Pesquisas Energéticas e Nucleares (IPEN). Este circuito é completamente constituído de tubos de vidro, o que permite a visualização e imageamento do escoamento monofásico e bifásico nos ciclos de circulação natural sob baixa pressão.Os resultados mostraram que o detector proposto conseguiu melhorar a identificação do contorno eficientemente em comparação aos detectores de contorno clássicos, sem a necessidade de fazer uso de algoritmos de suavização e sem intervenção humana. / This work has developed a new method for digital image contour detection which can be successfully applied to images presenting objects of interest with high proximity and presenting complexities related with background abrupt intensity fluctuations. The developed method makes use of fuzzy logic and declivity standard deviation (Fuzzy Declivity Standard Deviation FuzDec) to image processing and contour detection. Contour detection is an important task to estimate two-phase flow features through bubble segmentation in order to obtain parameters as void fraction and bubble diameter. FuzDec was applied to natural circulation instability images which were experimentally acquired. Image acquisition was done at the Natural Circulation Circuit (CCN) of the Instituto de Pesquisas Energéticas e Nucleares (IPEN) in Brazil. This facility is all made up with glass tubes allowing easy visualization and imaging of one-phase and two-phase flow patterns during natural circulation cycles under low pressures. Results confirm that the proposed detector can improve contour identification when compared to classical contour detector algorithms, without using smoothing algorithms or human intervention.

Made available in DSpace on 2017-07-10T19:24:30Z (GMT). No. of bitstreams: 1 LUIZ HENRIQUE BASSO.pdf: 2154844 bytes, checksum: 4e4e8b56f9c25a2ef13e0c7368a8197b (MD5) Previous issue date: 2008-06-27 / The awareness of the importance of the environment has stimulated the study of new energy sources renewed and less pollutant. Amongst these sources, solar energy stands alone for being perennial and clean. The use of solar energy in systems of residential water heating, instead of the electric shower, can compliment the economy of electric energy, based of the Brazilian energy matrix. To know all the factors that influence the operation of a system of water heating by solar energy is important in the determination of its economic viabilities, techniques and, distribution targeting in urban and agricultural residences. To evaluate equipment of water heating for solar energy in the region west of the Paraná, an archetype with similar characteristics to equipment used in residences for two inhabitants was built, to function with natural circulation or thermosiphon and without help of a complementary heating system. The room temperature and the speed of the wind were also evaluated, verifying its influence in the heating system. The equipment revealed technical viability, reaching the minimum temperature of 35°C for shower, whenever the solar radiation was above the 3500 W.m-2, for the majority of the studied days. The system operated without interruptions and it did not need maintenance, except for the monthly glass cleaning. Economic viability was clearly demonstrated since the useful life of the equipment exceeded the period of use to gain its investment. / A conscientização da importância do meio ambiente tem incentivado o estudo de novas fontes energéticas renováveis e menos poluentes. Dentre essas fontes, a energia solar se destaca por ser perene e limpa. A utilização da energia solar em sistemas de aquecimento de água residenciais, pela substituição do chuveiro elétrico, pode colaborar com a economia de energia elétrica, base da matriz energética brasileira. Conhecer todos os fatores que influenciam a operação de um sistema de aquecimento de água por energia solar é importante na determinação de suas viabilidades técnica e econômica, visando sua difusão em residências urbanas e rurais. Para avaliar um equipamento de aquecimento de água por energia solar na região oeste do Paraná, construiu-se um protótipo com características similares a um equipamento utilizado em residências para dois habitantes, para funcionar com circulação natural ou termossifão e sem auxílio de sistema de aquecimento complementar. A temperatura ambiente e a velocidade do vento também foram avaliadas, verificando-se sua influência no sistema de aquecimento. O equipamento mostrou-se viável tecnicamente, alcançando a temperatura mínima de 35°C para banho, sempre que a radiação solar foi superior a 3500 W.m-2, o que aconteceu para a maioria dos dias estudados. O sistema operou sem interrupções e não necessitou de manutenção, exceto pela limpeza mensal do vidro. Constatou-se a viabilidade econômica, já que a vida útil do equipamento é superior ao período de retorno do investimento.