Amebas de vida livre (AVL) são protozoários amplamente distribuídos na natureza e em ambientes artificiais. Alguns gêneros são oportunistas ou patogênicos, com característica anfizóica, são esses: Acanthamoeba spp., Naegleria spp., Balamuthia spp., Sappinia spp., e recentemente Vermamoeba spp. AVL podem servirem de reservatórios de várias bactérias patogênicas, uma vez que se alimentam dessas no ambiente por fagocitose, algumas espécies de bactérias após internalizadas escapam da via de degradação sobrevivem e multiplicam-se no interior das amebas. Face ao exposto, o presente trabalho objetivou isolar e identificar AVL e as bactérias associadas presentes em águas de torres de resfriamento, cuja temperatura da água varia entre 25 a 30°C (ideal para o desenvolvimento de diversos microrganismos). Amebas foram isoladas em cultivo monoxênico com Escherichia coli inativadas pelo calor. Das amostras positivas, foram realizadas Reações em Cadeia de Polimerase (PCR), utilizando oligonucleotídeos específicos para cada gênero. Os produtos das PCR foram sequenciados e as sequências geradas foram comparadas com sequências parciais de cada gene alvo depositadas no GenBank. Das 36 amostras, 33 (91,66%) foram positivas para presença de AVL, destas 15 (45,4%) foram positivas para Acanthamoeba spp., 12 (36,3%) para Naegleria spp., 6 (18,2%) para Vermamoeba spp. Dos endossimbiontes pesquisados, somente Pseudomonas spp. foram identificadas em 13 (39,3%) isolados de AVL. Os resultados obtidos no presente estudo confirmam a presença de amebas de vida livre potencialmente patogênicas e carreadoras de bactérias patogênicas oportunistas que podem representar um risco à saúde humana. / Free-living amoebae (FLA) are protozoa widely distributed in natural and artificial environments. Some genus are opportunistic or pathogenic, with anfizoic feature : Acanthamoeba spp., Naegleria spp., Balamuthia spp., Sappinia spp., and recently Vermamoeba spp. AVL may serve as reservoirs for various pathogenic bacteria, since they feed by phagocytosis in the environment, some species of bacteria after internalized escape to the pathway of degradation surviving and multiplying within the amoebae. The aim of this study was to isolate and identify FLA and their associated bacteria present in water from cooling tower, whose temperature water varies between 25 to 30 °C (ideal for the development of different organisms). Amoebae were isolated in monoxenic cultivation with Escherichia coli inactivated by heat. Of the positive samples Polymerase Chain Reactions (PCR) were performed using specific primers for each genus. The PCR products were sequenced and the sequences were generated compared with partial sequences of each gene target deposited in GenBank. From the 36 samples, 33 (91.66%) were positive for the presence of FLA. Of these, 15 (45.4%) were positive for Acanthamoeba spp., 12 (36.3%) for Naegleria spp. and 6 (18.2 %) for Vermamoeba spp. Of the amoeba isolated, 13 (39.3%) were associated to bacteria wich belong to Pseudomonas genus (100%). Another bacteria investigated were absent. The results of this study confirm the presence of potentially pathogenic free-living amoebae as vehicles of opportunistic/pathogenic bacteria that can pose a risk to the human health.

[pt] O objetivo deste estudo foi avaliar o efeito biocida do ácido peracético (APA) em águas de sistemas de resfriamento, de forma a buscar alternativas ao uso do cloro, que é corrosivo e reage com a matéria orgânica natural ou sintética presentes na água, formando subprodutos tóxicos. Para atingir este objetivo, experimentos utilizando amostras de água retiradas da bacia de uma torre de resfriamento de uma indústria química foram realizados. Ensaios foram executados utilizando-se uma solução comercial de APA, mantendo-se concentrações do biocida em 1,0 mgL-1 e 2,0 mgL-1 em pH 8,0 e 8,8. Cada condição de estudo foi monitorada ao longo de 5 dias, e contagens de bactérias heterotróficas mesófilas totais foram realizadas tanto antes da aplicação do biocida como em diferentes tempos de contato do biocida com a microbiota natural da água. Os tempos de contato monitorados foram de 5 min, além de 1, 2 e 4 h por dia considerando a aplicação do biocida em períodos totais de 4 h por dia. Com esta metodologia foi possível concluir que as duas dosagens aplicadas foram eficientes no combate aos microrganismos presentes naturalmente nas amostras de água, nos dois valores de pH estudados. A partir de uma carga microbiana natural da água de 106 a 107 UFC/mL, após o tratamento houve uma redução para contagens de no máximo de 104 UFC/mL em todos os experimentos, limite máximo esse adotado pelas indústrias para carga microbiana em águas de sistemas de resfriamento, entretanto, houve maior eficiência, cerca de 10 vezes maior, quando 2,0 mgL-1 de APA foi aplicado. Além disso, em pH 8,0 a ação do biocida também foi superior em 10 vezes em detrimento ao pH 8,8 para a mesma concentração de APA. / [en] The purpose of this study was to evaluate the biocidal effect of peracetic acid (PAA) in cooling water, in order to find alternatives to the use of chlorine, which is corrosive and reacts with natural and synthetic organic matter present in water, forming toxic byproducts. To achieve this goal, experiments using water samples taken from a basin of a chemical industry cooling tower were conducted. Experiments were performed using a commercial PAA solution, with concentrations of 1,0 mgL-1 and 2,0 mgL-1 and pH 8,0 and 8,8. Each study condition was monitored for 5 days and total mesophilic heterotrophic bacteria counts were made without biocide and after different contact times of the biocide and microorganisms present in water. The contact times were 5 min, and 1, 2 and 4 h per day, considering the application of the biocide in total periods of 4 h per day. This methodology has allowed concluding that two dosages applied were efficient in controlling microorganisms at the two pH values. From a water natural microbial count of 106 to 107 UFC/mL, after treatment there was a reduction to maximum counts to 104 UFC/mL in all experiments, that being the upper limit adopted by industries for microorganisms in cooling water systems. However, the results were 10 times more efficient when 2,0 mgL-1 of PAA were applied. In addition, at pH 8,0 the biocidal action was 10 times higher in comparison to pH 8,8 for the same PAA concentration.

Amebas de vida livre (AVL) são protozoários amplamente distribuídos na natureza e em ambientes artificiais. Alguns gêneros são oportunistas ou patogênicos, com característica anfizóica, são esses: Acanthamoeba spp., Naegleria spp., Balamuthia spp., Sappinia spp., e recentemente Vermamoeba spp. AVL podem servirem de reservatórios de várias bactérias patogênicas, uma vez que se alimentam dessas no ambiente por fagocitose, algumas espécies de bactérias após internalizadas escapam da via de degradação sobrevivem e multiplicam-se no interior das amebas. Face ao exposto, o presente trabalho objetivou isolar e identificar AVL e as bactérias associadas presentes em águas de torres de resfriamento, cuja temperatura da água varia entre 25 a 30°C (ideal para o desenvolvimento de diversos microrganismos). Amebas foram isoladas em cultivo monoxênico com Escherichia coli inativadas pelo calor. Das amostras positivas, foram realizadas Reações em Cadeia de Polimerase (PCR), utilizando oligonucleotídeos específicos para cada gênero. Os produtos das PCR foram sequenciados e as sequências geradas foram comparadas com sequências parciais de cada gene alvo depositadas no GenBank. Das 36 amostras, 33 (91,66%) foram positivas para presença de AVL, destas 15 (45,4%) foram positivas para Acanthamoeba spp., 12 (36,3%) para Naegleria spp., 6 (18,2%) para Vermamoeba spp. Dos endossimbiontes pesquisados, somente Pseudomonas spp. foram identificadas em 13 (39,3%) isolados de AVL. Os resultados obtidos no presente estudo confirmam a presença de amebas de vida livre potencialmente patogênicas e carreadoras de bactérias patogênicas oportunistas que podem representar um risco à saúde humana. / Free-living amoebae (FLA) are protozoa widely distributed in natural and artificial environments. Some genus are opportunistic or pathogenic, with anfizoic feature : Acanthamoeba spp., Naegleria spp., Balamuthia spp., Sappinia spp., and recently Vermamoeba spp. AVL may serve as reservoirs for various pathogenic bacteria, since they feed by phagocytosis in the environment, some species of bacteria after internalized escape to the pathway of degradation surviving and multiplying within the amoebae. The aim of this study was to isolate and identify FLA and their associated bacteria present in water from cooling tower, whose temperature water varies between 25 to 30 °C (ideal for the development of different organisms). Amoebae were isolated in monoxenic cultivation with Escherichia coli inactivated by heat. Of the positive samples Polymerase Chain Reactions (PCR) were performed using specific primers for each genus. The PCR products were sequenced and the sequences were generated compared with partial sequences of each gene target deposited in GenBank. From the 36 samples, 33 (91.66%) were positive for the presence of FLA. Of these, 15 (45.4%) were positive for Acanthamoeba spp., 12 (36.3%) for Naegleria spp. and 6 (18.2 %) for Vermamoeba spp. Of the amoeba isolated, 13 (39.3%) were associated to bacteria wich belong to Pseudomonas genus (100%). Another bacteria investigated were absent. The results of this study confirm the presence of potentially pathogenic free-living amoebae as vehicles of opportunistic/pathogenic bacteria that can pose a risk to the human health.

L'implication des tours aéro-réfrigérantes dites « ouvertes », dans les cas de légionellose, demeure à l'heure actuel un problème de santé public malgré la multitude de composés biocides disponibles qui, parfois, sont écotoxiques et appliqués à de forte concentrations. L'efficacité de la majorité de ces biocides est étudiée vis-à-vis des formes planctoniques des microorganismes. Cette étude s'intéresse à la mise au point de deux procédés de traitement du risque Legionella pneumophila : H2O2/UV et ClO2, avec la prise en compte particulière des communautés microbiennes fixées et notamment des protozoaires qui constituent l'hôte naturel de cette bactérie. La démarche expérimentale adoptée pour l'étude de l'efficacité de ces traitements, s'est appuyée sur des biofilms environnementaux naturellement contaminés par des légionelles et issus d'une source thermale. La caractérisation des légionelles isolées des biofilms de cette source montre le maintien du sérogroupe 1 de L. pneumophila et l'apparition de deux autres sérogroupes non reportés dans des études précédentes (sg10 et sg12), avec toutefois une prédominance du sérogroupe 12. Quel que soit le sérogroupe, ces souches environnementales se sont avérées plus virulentes vis-à-vis de l'amibe Acantamoeba castellanii, que les souches cliniques de Lp1 répertoriées. A l'état planctonique elles se sont également avérées très sensibles aux traitements H2O2/UV et UV seul. A l'échelle expérimentale, les deux traitements, H2O2/UV et ClO2, montrent une performance élevée vis-à-vis des biofilms. L'étude a particulièrement mis en évidence le rôle du facteur trophique et de l'adaptation des bactéries au stress oxydatif dans la performance des traitements mais aussi dans l'apparition de la reviviscence. L'application des traitements à des installations en vraie grandeur a permis de conforter les résultats expérimentaux et de mettre l'accent, dans le contexte des sites étudiés, sur les limites de leur efficacité et sur la nécessité d'ajustements des doses appliquées (concentrations des biocides, flux d'irradiation UV, mode d'application) aux particularités des contextes industriels. / Cooling towers are considered as one of the major sources of Legionella pneumophila, the causal agent of Legionnaires' disease. Despite the high number of commercial disinfectants dedicated to it, the Legionella threat is still rising especially in connection with cooling towers. The efficacy of most disinfectants is demonstrated on planktonic bacteria while very few studies have been devoted to their effects on biofilms. The main objective of the study was to optimize two treatments dedicated to the control of biofilms in cooling towers, H2O2/UV and ClO2, so as to reduce the risk associated to Legionella pneumophila while minimizing environmental damages. Their efficacy was studied against environmental biofilms developed in a hot sulphur spring where presence of L. pneumophila is permanent. Their analysis revealed the occurrence of Lp serogroups 1 (Lp1) and of two serogroups not reported in previous studies that were oriented toward water samples, though (Lp10 and Lp12). The environmental strains we isolated display a higher cytotoxicity and virulence towards the amoeba Acantamoeba castellanii than those of known Lp1 epidemic strains and a higher sensitivity to UV and H2O2/UV. In the experimental part of the study, ClO2 and H2O2/UV display a high efficacy against biofilms. Furthermore the study showed the role of trophic parameters and of bacterial adaptation to oxidative stress on the performance of the treatments but also on biofilms regrowth. The experiments performed at the industrial scale corroborate the results gained at the pilot scale and focus on the relationships between the dose and the effectiveness of each treatment. Our results suggest the possibility to apply the process to an industrial scale with necessary adjustments about doses and injection modalities to the context of the considered sites.

Amebas de vida livre (AVL) são protozoários amplamente distribuídos na natureza e em ambientes artificiais. Alguns gêneros são oportunistas ou patogênicos, com característica anfizóica, são esses: Acanthamoeba spp., Naegleria spp., Balamuthia spp., Sappinia spp., e recentemente Vermamoeba spp. AVL podem servirem de reservatórios de várias bactérias patogênicas, uma vez que se alimentam dessas no ambiente por fagocitose, algumas espécies de bactérias após internalizadas escapam da via de degradação sobrevivem e multiplicam-se no interior das amebas. Face ao exposto, o presente trabalho objetivou isolar e identificar AVL e as bactérias associadas presentes em águas de torres de resfriamento, cuja temperatura da água varia entre 25 a 30°C (ideal para o desenvolvimento de diversos microrganismos). Amebas foram isoladas em cultivo monoxênico com Escherichia coli inativadas pelo calor. Das amostras positivas, foram realizadas Reações em Cadeia de Polimerase (PCR), utilizando oligonucleotídeos específicos para cada gênero. Os produtos das PCR foram sequenciados e as sequências geradas foram comparadas com sequências parciais de cada gene alvo depositadas no GenBank. Das 36 amostras, 33 (91,66%) foram positivas para presença de AVL, destas 15 (45,4%) foram positivas para Acanthamoeba spp., 12 (36,3%) para Naegleria spp., 6 (18,2%) para Vermamoeba spp. Dos endossimbiontes pesquisados, somente Pseudomonas spp. foram identificadas em 13 (39,3%) isolados de AVL. Os resultados obtidos no presente estudo confirmam a presença de amebas de vida livre potencialmente patogênicas e carreadoras de bactérias patogênicas oportunistas que podem representar um risco à saúde humana. / Free-living amoebae (FLA) are protozoa widely distributed in natural and artificial environments. Some genus are opportunistic or pathogenic, with anfizoic feature : Acanthamoeba spp., Naegleria spp., Balamuthia spp., Sappinia spp., and recently Vermamoeba spp. AVL may serve as reservoirs for various pathogenic bacteria, since they feed by phagocytosis in the environment, some species of bacteria after internalized escape to the pathway of degradation surviving and multiplying within the amoebae. The aim of this study was to isolate and identify FLA and their associated bacteria present in water from cooling tower, whose temperature water varies between 25 to 30 °C (ideal for the development of different organisms). Amoebae were isolated in monoxenic cultivation with Escherichia coli inactivated by heat. Of the positive samples Polymerase Chain Reactions (PCR) were performed using specific primers for each genus. The PCR products were sequenced and the sequences were generated compared with partial sequences of each gene target deposited in GenBank. From the 36 samples, 33 (91.66%) were positive for the presence of FLA. Of these, 15 (45.4%) were positive for Acanthamoeba spp., 12 (36.3%) for Naegleria spp. and 6 (18.2 %) for Vermamoeba spp. Of the amoeba isolated, 13 (39.3%) were associated to bacteria wich belong to Pseudomonas genus (100%). Another bacteria investigated were absent. The results of this study confirm the presence of potentially pathogenic free-living amoebae as vehicles of opportunistic/pathogenic bacteria that can pose a risk to the human health.

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

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.

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.

Thesis (PhD (Mechanical and Mechatronic Engineering))--University of Stellenbosch, 1995. / Computer simulation programs were developed for the analysis of dry-cooling systems for power plant applications. Both forced draft direct condensing air"cooled condensers and hyperbolic natural draft indirect dry-cooling towers are considered. The results of a considerable amount of theoretical and experimental work are taken into account to model all the physical phenomena ofthese systems, to formu1ate the problems in formal mathematical terms and to design and apply suitable computational algorithms to solve these problems effectively and reliably. The dry-cooling systems are characterized by equation-based models. These equations are simultaneously solved by a specially designed constrained nonlinear least squares algorithm to determine the performance characteristics of the dry-cooling systems under fixed prescnoed operating conditions, or under varying operating conditions when coupled to a turbo-generator set. The solution procedure is very fast and effective. A capital and operating cost estimation procedure, based on information obtained from dry-cooling system component manufacturers and the literature, is proposed. Analytical functions express the annual cost in terms ofthe various geometrical and operating parameters ofthe dry-cooling systems. The simu1ation and the cost estimation procedures were coupled to a constrained nonlinear programming code which enable the design of minimum cost dry-cooling systems at fixed prescribed operating conditions, or dry-cooling systems which minimize the ratio of total annual cost to the annual net power output of the corresponding turbo-generator set. Since prevailing atmospheric conditions, especially the ambient temperature, influence the performance of dry-cooling systems, wide fluctuations in turbine back pressure occur. Therefore, in the latter case the optimal design is based on the annual mean hourly frequency ofambient temperatures, rather than a fixed value. The equation-based models and the optimization problems are simultaneously solved along an infeasible path (infeasible path integrated approach). The optimization model takes into consideration all the parameters that may affect the capital and operating cost of the dry-cooling systems and does not prescribe any limits, other than those absolutely essential due to practical limitations and to simulate the systems effectively. The influence that changes ofthe constraint limits and some problem parameters have on the optinmm solution, are evaluated (sensitivity analysis). The Sequential Quadratic Programming (SQP) method is used as the basis in implementing nonlinear optimization techniques to solve the cost minimirnti~n problems. A stable dual active set algorithm for convex quadratic programming (QP) problems is implemented that makes use of the special features ofthe QP subproblems associated with the SQP methods. TIrls QP algorithm is also used as part of the algorithm that solves the constrained nonlinear least squares problem This particular implementation of the SQP method proved to be very reliable and efficient when applied to the optimization problems based on the infeasible path integrated approach. However, as the nonlinear optimization problems become large, storage requirements for the Hessian matrix and computational expense of solving large quadratic programming (QP) subproblems become prohibitive. To overcome these difficulties, a reduced Hessian SQP decomposition strategy with coordinate bases was implemented. This method exploits the low dimensionality of the subspace of independent decision variables. The performance of this SQP decomposition is further improved by exploiting the mathematical structure of the engineering model, for example the block diagonal structure ofthe Jacobian matrix. Reductions ofbetween 50-90% in the total CPU time are obtained compared to conventional SQP optimization methods. However, more function and gradient evaluations are used by this decomposition strategy. The computer programs were extensively tested on various optimization problems and provide fast and effective means to determine practical trends in the manufacturing and construction of costoptimal dry-cooling systems, as well as their optimal performance and operating conditions in power plant applications. The dissertation shows that, through the proper application of powerful optimization strategies and careful tailoring of the well constructed optimization model, direct optimization of complex models does not need to be time consuming and difficult. Reconnnendations for further research are made. / Imported from http://etd.sun.ac.za April 2010.