Orientador: Roger Josef Zemp / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Química / Made available in DSpace on 2018-08-21T01:23:18Z (GMT). No. of bitstreams: 1 Jasiulionis_JaquelineAndreaEsposito_M.pdf: 15957742 bytes, checksum: f23f7bfae46e12833b047fae94479804 (MD5) Previous issue date: 2012 / Resumo: Em muitos processos há necessidade de remover a carga térmica de um dado sistema e utiliza-se, na maioria dos casos, a água como o fluido de resfriamento. Devido à sua crescente escassez e preocupação com o meio ambiente, além de motivos econômicos, a água "quente" que sai desses processos, deve ser aproveitada. Para tanto, ela passa por uma torre de resfriamento e retorna ao processo. Este trabalho descreve um procedimento para avaliar o desempenho térmico de torres de resfriamento, em duas configurações distintas (escoamento contracorrente e escoamento cruzado), utilizando redes neurais artificiais. A vantagem do procedimento proposto é a possibilidade da avaliação direta do desempenho de uma torre sem a complexidade do uso de procedimentos iterativos para convergência nem a necessidade de rotinas de propriedades físicas e psicrométricas. A avaliação do desempenho é feita pela determinação da temperatura de saída da água para um conjunto de parâmetros de entrada (propriedades de corrente da água e do ar na entrada da torre, dimensões e propriedades do recheio), ou determinação da característica do recheio para uma torre existente, em função das condições operacionais. Para a situação de projeto o procedimento permite estimar a vazão de ar ou altura necessária para a torre satisfazer uma condição operacional exigida. O procedimento proposto se mostrou particularmente eficiente para torres com escoamento cruzado, onde o método tradicional de simulação exige a decomposição da torre em um número elevado de células, cada um como um procedimento iterativo para cálculo do balanço de massa e energia. A rede rendeu ótimos resultados quando usada para predizer a temperatura de saída da água e o coeficiente de transferência de massa. Os resultados mostram que a RNA pode fornecer com precisão o desempenho térmico da torre de resfriamento / Abstract: In many industrial environments it is necessary to remove the heat load from a given system and in most cases water is used as the coolant. Due to its increasing scarcity and concerns for the environment, and economic reasons, the "hot" water coming out of these processes must be reused. To do so, it passes through a cooling tower and returns to the process. This paper describes a procedure for evaluating the thermal performance of cooling towers in two different configurations (counter flow and cross flow), using artificial neural networks. The advantage of the proposed procedure is the possibility of direct assessment of the performance of a tower without the complexity due to the required convergence of the iterative procedure or the need for physical properties and psychrometric routines. The performance evaluation is made by computing the temperature of the water outlet for a set of input parameters (flow properties of water and air near the tower, dimensions and properties of the filling), or computing the characteristic of the filling for a existing tower, depending on operating conditions. For the project situation, the procedure allows for the estimate of the air flow or the tower height needed to meet a required operating condition. The proposed procedure proved particularly effective in cross-flow towers, where the traditional method of simulation requires the decomposition of the tower in a large number of cells, each as an iterative procedure for calculating the mass balance and energy. The network yielded excellent results when used to predict the exit temperature of the water and the coefficient of mass transfer. The results show that the RNA can accurately provide the thermal performance of the cooling tower / Mestrado / Sistemas de Processos Quimicos e Informatica / Mestra em Engenharia Química

Although Anthony Trollope has traditionally been considered an anti-feminist author, studies within the past decade have shown that Trollope's later novels show support for female power and sympathy for Victorian women who were dissatisfied with their narrow roles in society. A feminist reading of two of his earliest novels, The Warden and Barchester Towers, shows that Trollope's feminism is not limited to his later works. In The Warden, Trollope acclaims female power and "woman's logic" through female characters and the womanly warden, Septimus Harding. In Barchester Towers, Trollope continues to support feminism through his positive portrayals of strong, independent women and the androgynous Harding. In Barchester Towers, the battle of the sexes ends in a balance of power.

Orientadores: José Pissolato Filho, Eduardo Coelho Marques da Costa / Tese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia Elétrica e de Computação / Made available in DSpace on 2018-08-24T10:02:40Z (GMT). No. of bitstreams: 1 Pinto_AndreJinnoGomes_D.pdf: 9708757 bytes, checksum: 84772389fed6b8c0c68adcdd4db7cd9b (MD5) Previous issue date: 2014 / Resumo: A análise do comportamento dinâmico da torre de transmissão de energia elétrica e torres de telecomunicações é de interesse nos estudos de proteção relacionados com descargas atmosféricas. Normalmente, a impedância de surto da torre no domínio do tempo é usada para caracterizar o comportamento dinâmico da torre. A principal desvantagem na definição de tais impedâncias de surto é a dependência da forma de onda de excitação, e não há consenso sobre a forma de onda de corrente a ser usada. Além disso, não há concordância sobre uma definição única da tensão envolvida. A fim de contornar tais limitações e problemas, o modelo aplicado ao estudo faz uso das análises no dominio da frequência, onde a impedância de surto da torre depende somente da geometria da estrutura e das características eletromagnéticas do meio. Ademais, as limitações associadas com as abordagens simplificadas são enfatizadas no decorrer do presente trabalho. Os resultados apresentados fazem uso de ferramentas computacionais como o código NEC-2 (Numerical Electromagnetic Code) que se baseia na análise numérica da dinâmica do campo eletromagnético. Com a utilização desse código, correntes são geradas e posteriormente utilizadas para o cálculo da impedância de surto da torre. Posteriormente, é gerado um circuito RLC representativo das características da estrutura metálica, obtidas pelo método de vector fitting que aproxima a função impedância de surto da torre por funções racionais. Por fim, o circuito RLC gerado pode ser aplicado nas análises diretamente no domínio do tempo com o uso de programas computacionais como o EMTP (Electromagnetic Transients Program), sem a necessidade do uso de transformadas para alterar o domínio de análise / Abstract: The dynamic analysis of the behavior in power transmission towers and telecommunications towers is of interest in studies related to lightning protection. Normally, the surge impedance of the tower in the time domain is used to characterize the dynamic behavior of the tower. The main disadvantage of these definition of surge impedances is the dependence on the waveform of excitation, and there is no consensus on which current wave to be used. Furthermore, there is no agreement on a single definition of the voltage involved. In order to overcome such limitations and problems, the model applied to the study makes use of the analysis in the frequency domain, where tower¿s surge impedance depends only on the geometry of the structure and electromagnetic characteristics of the medium. Moreover, the limitations associated with the simplified approaches are emphasized in the course of this work. The results presented make the use of computer code as NEC-2 (Numerical Electromagnetic Code) based on the numerical analysis of the electromagnetic field dynamics. Using this code, currents are generated and then used to calculate the surge impedance of the tower. Subsequently, an RLC circuit is generated representating the characteristics of the metal structure, obtained by vector fitting method, that approximates the surge impedance function of the tower by means of rational functions. Finally, the generated RLC circuit can be applied directly in analyzes in the time domain using computer programs such as EMTP (Electromagnetic Transients Program) without the need of using transforms to change domain analysis / Doutorado / Energia Eletrica / Doutor em Engenharia Elétrica

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Thesis (MScEng)--Stellenbosch University, 2012. / ENGLISH ABSTRACT: A wet-cooling tower fill performance evaluation model developed by Reuter is derived in Cartesian coordinates for a rectangular cooling tower and compared to cross- and counterflow Merkel, e-NTU and Poppe models. The models are compared by applying them to a range of experimental data measured in the cross- and counterflow wet-cooling tower test facility at Stellenbosch University. The Reuter model is found to effectively give the same results as the Poppe method for cross- and counterflow fill configuration as well as the Merkel and e-NTU method if the assumptions as made by Merkel are implemented. A second order upwind discretization method is applied to the Reuter model for increased accuracy and compared to solution methods generally used to solve cross- and counterflow Merkel and Poppe models. First order methods used to solve the Reuter model and crossflow Merkel and Poppe models are found to need cell sizes four times smaller than the second order method to obtain the same results. The Reuter model is successfully implemented in two- and three-dimensional ANSYS-Fluent® CFD models for under- and supersaturated air. Heat and mass transfer in the fill area is simulated with a user defined function that employs a second order upwind method. The two dimensional ANSYS-Fluent® model is verified by means of a programmed numerical model for crossflow, counterflow and cross-counterflow. / AFRIKAANSE OPSOMMING: ‘n Natkoeltoring model vir die evaluering van pakkings werkverrigting, wat deur Reuter ontwikkel is, word in Kartesiese koördinate afgelei vir ‘n reghoekige koeltoring en word vergelyk met kruis- en teenvloei Merkel, e-NTU en Poppe modelle. Die verskillende modelle word vergelyk deur hulle op ‘n reeks eksperimentele data toe te pas wat in die kruis- en teenvloei natkoeltoring toetsfasiliteit by die Universiteit van Stellenbosch gemeet is. Dit is bevind dat die Reuter model effektief dieselfde resultate gee as die Poppe model vir kruis- en teenvloei pakkingskonfigurasies sowel as die Merkel en e-NTU metode, indien dieselfde aannames wat deur Merkel gemaak is geїmplementeer word. ‘n Tweede orde “upwind” metode word op die Reuter model toegepas vir hoër akkuraatheid en word vergelyk met oplossingsmetodes wat gewoonlik gebruik word om kruis- en teenvloei Merkel en Poppe modelle op te los. Eerste orde metodes wat gebruik is om die Reuter model en kruisvloei Merkel en Poppe modelle op te los benodig rooster selle wat vier keer kleiner is as vir tweede orde metodes om dieselfde resultaat te verkry. Die Reuter model is suksesvol in twee- en driedimensionele ANSYS-Fluent® BVD (“CFD”) modelle geїmplementeer vir on- en oorversadigde lug. Warmte- en massaoordrag in die pakkingsgebied word gesimuleer mbv ‘n gebruiker gedefinieerde funksie (“user defined function”) wat van ‘n tweede orde numeriese metode gebruik maak. Die tweedimensionele ANSYS-Fluent® model word m.b.v. ‘n geprogrameerde numeriese model bevestig vir kruis-, teen- en kruis-teenvloei.

Thesis (MScEng (Mechanical and Mechatronic Engineering))--University of Stellenbosch, 2006. / Cooling tower spray nozzle performance characteristics such as the water distribution onto the fill material, air side pressure drop, pump head, drop size distribution and heat transfer in the spray zone were investigated experimentally and theoretically. The aim was to evaluate and simulate the performance characteristics of new and existing types of cooling tower spray nozzles with emphasis on the spray zone. Two medium and two low pressure type spray nozzles were tested and the results analysed. Single nozzle water distribution data obtained from tests was used to predict the water distribution obtained from four evenly spaced nozzles by superposition. The results were compared to data obtained from corresponding four nozzle tests. Computer codes and CFD models were developed to predict the drop trajectories, water distribution, total heat transfer and pressure drop for single nozzles and four nozzle grids. This was compared to correlated data found in literature. The performance characteristics expected from an ideal nozzle was discussed and compared to actual nozzle performance characteristics.

M. Tech. Business Administration / The research reviews how the implementation of total productive maintenance (TPM), as a maintenance strategy, can be adopted at DCD Wind Towers (Pty) Ltd., a wind tower manufacturing company in South Africa. It also focuses on maintenance management programmes, identifies obstacles, barriers and challenges to the implementation of maintenance management programmes.

Thesis (MEng) -- Stellenbosch University, 2014. / ENGLISH ABSTRACT: Water collection systems are used in wet-cooling towers (WCTs) with fill over which water to be cooled flows and in evaporative air-cooled heat exchangers (EACHEs) having deluged tube bundles over which water flows to transfer heat from the tubes. They collect and remove water falling from the bottom of the fill or heat exchanger tube bundle while allowing air to pass with limited flow resistance. There are basically two types of collection systems, categorized as trough and basin systems. Trough systems comprise of multiple, evenly spaced parallel troughs extended in one direction with inclined capture plates to direct water into the troughs. The water collects in the troughs and drains under gravity to a collecting tank or manifold from where it is pumped to the sprayers. In basin systems water falls directly into an open basin under gravity where it is collected and can be pumped to the sprayers. The hybrid (dry/wet) dephlegmator (HDWD) for air-cooled steam condensers, which is being developed at Stellenbosch University as discussed by Heyns (2008), Owen (2013) and Anderson (2014), requires a more effective water collection system with a lower pressure drop than what current designs have to offer. In this thesis, an existing trough system is systematically evaluated by means of various high speed camera and flow experiments to determine its performance characteristics and to find ways to improve its catchment effectiveness. A modification is proposed which increases the effectiveness from approximately 92% to 100 % with a relatively small increase in pressure drop, by adding a small deflector plate and reducing the spacing between adjacent troughs. Experimental data and CFD models are used to determine the performance characteristics of the modified trough system for design purposes. For comparison, various basin system designs are proposed and investigated using CFD, where the baseline model is validated by means of experimental data of rectangular cooling tower inlets by Kröger (2004). Rectangular cooling tower inlets are relevant as they have a similar re-circulating flow pattern to what is seen with the water basin inlets at the vicinity of the inlet wall. The numerical data is correlated to determine empirical relations for the flow performance characteristics. The comparison between the modified trough and the different basin systems yields that the trough system requires significantly less fan and pumping power than basin systems and the costs are also expected to be less. / AFRIKAANSE OPSOMMING: Wateropvangstelsels word gebruik in nat koeltorings en verdamping verkoelers, waar waterdruppels in teen-vloei is met n lugstroom. Die stelsel vang die water wat val op en verwyder dit uit die lugstroom met 'n minimale lugweerstand. Daar is twee wateropvangstelsels wat as volg gekategoriseer word: trog stelsel en wateropvangbak stelsel. 'n Trog stelsel bestaan uit eweredige gespasieerde trôe parallel aan mekaar met 'n skuinsvlak om water in die kanaal op te vang. Water dreineer as gevolg van swaartekrag na 'n opvangs tenk waarvan dit terug gepomp word na die sproeiers. In 'n wateropvangbak stelsel val water direk in die bak en word terug gepomp na die sproeiers. 'n Lugverkoelde kondenserstelsels met 'n hibriede (droog/nat) deflegmator wat huidiglik by die Stellenbosch Universiteit ontwikkel word benodig 'n meer effektiewe wateropvangstelsel met 'n lae drukval. In hierdie tesis word bestaande trog stelsels sistematies geëvalueer deur middel van verskeie toetse met 'n hoë spoed kamera en lugvloei eksperimente om die werkverrigtingskarakteristieke te bepaal en om die opvangsvermoë te verbeter. 'n Verbetering word voorgestel wat die opvangsvermoë verbeter van ongeveer 92 % na 100 % met 'n relatiewe klein verhoging in die drukval deur 'n klein leilem by te voeg en die spasiëring tussen trôe te verminder. Eksperimentele data en BVD (berekeningsvloeidinamika) modelle word gebruik om die werkverrigtingskarakteristieke te bepaal van die nuwe trog stelsel vir ontwerps doeleindes. Die modelle is bekragtig deur gebruik te maak van literatuur van inlaatverlies korrelasies vir reghoekige koeltorings, soos gedoen deur Kröger (2004). Die inlaat van reghoekige koeltorings het soortgelyke vloeipatrone en vloeiwegbreking soos wat by die inlaat van die wateropvangbak stelsel gesien word. Die numeriese data word gebruik om 'n vergelyking vir die vloei karakteristieke te bepaal. 'n Vergelykende studie tussen die nuwe trog stelsel en die wateropvangbak stelsel het bewys dat die trog stelsel noemenswaardig minder waaier drywing en pomp drywing benodig.