Dissertations / Theses on the topic 'Refrigeration plant'

The objective of this study was to develop, install, and test a small underground mobile refrigeration plant (M.R.P.) to deal with some of the real problems associated with mine cooling in an operating mine. The requirement for cooling the underground environment is discussed with particular emphasis on the need for this method of cooling, with the concomitant benefits. The research investigated current methods of cooling and reasons for previous failures in (M.R.P.). Both static and dynamic simulations were conducted to increase the confidence level under operating conditions. Implementation and testing, resulted in "lessons learnt" requiring modifications, which are documented. Actual results have been recorded. These results have proved that significant cooling via (M.R.P) is feasible. Main benefits include positional efficiency, cost per kilowatt of cooling and cooling opportunities for remote areas of a mine. Finally, a proven technology is now available for large-scale implementation into the mining industry. Now the ventilation engineer has another system of cooling, which can be utilized in the quest to create an occupational environment, which meets the physical and mental health requirements of the worker.
Thesis (M.Ing.)--North-West University, Potchefstroom Campus, 2003.

This research focusses on utilising low temperature waste heat from a rural renewable power plant for absorption refrigeration. It forms part of a collaborative "Bridging the Urban Rural Divide" (BURD) research group across the United Kingdom and India investigating rural sustainable development through the provision of renewable electricity. The group is tasked with improving the educational environment and healthcare of a 45 household community (which is part of a larger village) in West Bengal, India. Working in collaboration with the Indian Institute of Technology Bombay as part of this thesis, a projected daily electrical demand for the community of 55 kW∙h per day was calculated, providing: lighting, fans and an electrical device charging station. To allow in excess of the daily electrical demand as well as for system ancillaries at 12 kW∙h, solar trackers at 14 kW∙h and 7 kW∙h for hydrogen production, a power plant producing 90 kW∙h was specified. This included daily electricity production of 70 kW∙h during the daytime from solar via a 10 kW concentrated photovoltaic (CPV) system and 20 kW∙h in the evening from a 5 kW biogas and hydrogen internal combustion engine electrical generator (genset). The biogas is produced from anaerobic digestion of food waste and aquatic weeds, and the hydrogen is produced from the electrolysis of water in an electrolyser powered by excess solar power. An energy and exergy analysis identified the daily quantity and quality of recoverable waste heat sources at 25°C. These are the CPV with an energetic value of 109 kW∙h and an exergetic value of 32 kW∙h at 60°C and the genset radiator with an energetic value of 32 kW∙h and an exergetic value of 5 kW∙h at 80°C. The exhaust heat from the genset has been allocated for other uses and, though calculated, is outside the scope of this research. The thesis then focusses on using these low temperature waste heat sources for absorption refrigeration. The working fluids selected are acetone and zinc bromide as these had been proven in the literature to operate at temperatures below those of the expected waste heat sources without the need for rectification (the process of separating two fluid vapours from each other). Due to the local climate with high ambient temperatures, averaging 24°C to 35°C, and the relatively low waste heat source temperatures, a number of configurations of absorption refrigerator were investigated to achieve lower, and therefore more versatile, evaporator temperatures. Some of these involve utilising some of the cooling produced from either or both of the heat sources to cool the absorber and condenser. The findings were that the most energy effective way of providing low evaporator temperatures was to use a small (2%) difference in weak and strong solution concentrations and not use a proportion of the cooling generated for the absorber or condenser. By operating two independent refrigerators powered by each heat source independently, the solution concentrations could be optimised to provide the lowest possible evaporator temperatures at a given ambient temperature. At the 25°C reference ambient temperature used for the energy and exergy analysis, the CPV waste heat can provide 33.4 kW∙h of continuous cooling per day at 6°C and the genset radiator 6.3 kW∙h at 0°C. This cooling energy collectively is sufficient to replace 12.7 kW∙h of electricity that would have been used to power a vapour compression refrigerator to provide the same amount of cooling, which is equal to 22% of the electrical power provided to the village. The genset waste heat source used for absorption refrigeration can provide cooling for food and medicine storage equivalent to 6 to 8 domestic refrigerators. The CPV waste heat source can provide space cooling for a room in a health centre for 6 to 9 hours per day. The investigations within this thesis highlighted the need for intelligent control systems to optimise the availability and temperatures of the refrigerators during unfavourable ambient conditions.

O mercado mundial de floricultura gera um fluxo de quase US$ 7bilhões anuais, atualmente concentrado em países como Holanda, Alemanha, Itália, Colômbia, Costa Rica, Equador, Quênia, Tailândia, Malásia, Israel e EUA. O Brasil ainda contribui pouco, aproximadamente 0,3% do total, sendo a participação brasileira concentrada na exportação de mudas, bulbos, flores e folhagens tropicais. O Brasil possui grande potencial exportador de flores e plantas ornamentais através da organização dos produtores, profissionalização do setor, apoio governamental e desenvolvimento técnico. O emprego de técnicas simples de armazenamento poderia viabilizar o transporte por modais que não o aéreo, reduzindo custos e podendo prolongar a vida útil dos produtos, criando um diferencial de qualidade em relação aos concorrentes. Este trabalho compara cinco diferentes tipos de recobrimento em estacas de Cordyline rubra Hügel (película amilácea, pasta de parafina no ápice, pasta de parafina no ápice e vermiculita umedecida na base, saco plástico ou sem recobrimento), sazonalidade (estacas coletadas durante primavera ou outono), dois ambientes de armazenamento (ambiente refrigerado a 10ºC ou temperatura ambiente 22-32ºC) e diferentes períodos de armazenamento (30, 60, 90 ou 120 dias), a fim de reduzir sua atividade biológica, perda de água e ataque de patógenos. Foi escolhida esta espécie por ser muito apreciada como planta ornamental devido à beleza de suas folhas, e exportada na forma de estacas de diferentes tamanhos. O experimento foi conduzido nas dependências do Departamento de Produção Vegetal da Escola Superior de Agricultura “Luiz de Queiroz”, Universidade de São Paulo, no município de Piracicaba, Estado de São Paulo. Foram utilizadas 615 estacas com 30 cm de comprimento por 3 cm de diâmetro. Um lote testemunha sem armazenamento de 15 estacas foi colocado em leito de enraizamento. Cada tratamento foi composto por 30 estacas pré-tratadas (tipos de recobrimento), submetidas a diferentes períodos de armazenamento (30, 60, 90 ou 120 dias), sendo divididos em 2 sub-tratamentos de 15 estacas (temperatura ambiente ou refrigerada), totalizando 120 estacas. Após o armazenamento foram cortados 3 cm da base de cada estaca, em seguida tratadas com IBA a 10.000 mg/L e colocadas em leito de enraizamento. Após 90 dias foram avaliados os seguintes parâmetros: porcentagem de desenvolvimento, número e massas de matéria fresca e seca de brotos, raízes e rizomas. Observou-se que as estacas colhidas na primavera apresentaram melhor enraizamento e produção de massas secas e frescas. Os menores períodos de armazenamento proporcionam melhor desenvolvimento das estacas, bem como estacas armazenadas em ambiente refrigerado apresentaram melhores resultados do que as mantidas em temperatura ambiente. Os tipos de recobrimento que melhor conservaram as estacas, em ordem decrescente de resultados, foram o saco plástico, parafina no ápice e vermiculita umedecida na base, parafina no ápice, película de amido e sem recobrimento. Conclui-se que o método mais prático foi embalar as estacas em sacos plásticos por não necessitar de fonte de calor para o preparo da película. Quanto maiores os períodos de armazenamento, menores desenvolvimentos de brotos, raízes e rizomas; os melhores resultados foram obtidos com estacas colhidas na primavera e armazenadas em ambiente refrigerado.
The world market of floriculture, generates an annual flow of US$ 7billion, is currently based on countries like The Netherlands, Germany, Italy, Colombia, Costa Rica, Ecuador, Kenya, Thayland, Malaysia, Israel and the USA. The Brazilian contribution to the total world market is approximately 0.3%, where the mains exports are cuttings, bulbs, tropical fresh cut flowers and foliages. Brazil, however, has a great potential to increase its export of flowers and other ornamental plants through the better organization of producers, professionalization of the sector, government support and technical development. The use of simple storage techniques, would enable the transport through other means than airplanes, consequently reducing costs and adding extra shelf life to the product, creating a quality differentiation in relation to competitors. This work was aimed at comparing five types of coating of Cordyline rubra Hügel cuttings (starch film, paraffin paste at the apex, paraffin past at the apex associated with moist vermiculite at the base of the cuttings, plastic bags or no coating), seasonality (cuttings harvested during spring or autumn), two types of enviromental temperatures (refrigeration under 10ºC or environmental temperature between 22-32ºC) and different lengths of time on storage (30, 60, 90 or 120 days), in order to reduce their biologycal activity, water loss and pathogen attacks. This specie is very appreciated as an ornamental plant due to the beauty of their foliage and is exported as cuttings of different sizes. The experiment was carried out at the Departament of Plant Production at “Luiz de Queiroz” College of Agriculture, University of Sao Paulo, in Piracicaba City, Sao Paulo State, Brazil. A total of 615 cuttings were used, each measuring 30 cm by 3 cm diameter. A control group of 15 cuttings without storage was planted on rooting bed. Each treatment was comprised of 30 pre-coated cuttings (types of coating), stored at different periods (30.60, 90 or 120 days) and split into 2 sub-treatments of 15 cuttings, either stored at room temperature or under refrigeration, summing up 120 cuttings. After storage, each cutting had 3 cm excised from its base, prior to being treated with IBA 10.000 mg/L and placed at rooting beds. After 90 days, the following parameters were assessed: percentage of cuttings showing growth and development, number and fresh and dry matter of the shoots, roots and rhizoms. It was observed that cuttings obtained during the spring, showed better rooting and production of biomass. The shorter the storage periods the better the cutting sprouting. Cuttings stored under refrigeration showed better results than kept under room temperature. The types of coatings which best supported the longevity of the cuttings, in decrease order, were: plastic bag, paraffin paste at the apex and moist vermiculite at the base, paraffin on the apex, starch film and no coating. Such results allow to conclude that the most practical coating technique was found to be the use of plastic bags, which did not need heating for the prepare of the film. The longer the storage time the smallest the number of viable cuttings; best results where observed for cuttings harvested during the spring and kept under refrigeration storage.

Orientador: Flávio Vasconcelos da Silva
Tese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia Química
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Resumo: Os sistemas de refrigeração estão presentes em diferentes ramos da indústria e caracterizam-se como grandes consumidores de energia com considerável comportamento não-linear. Inúmeros trabalhos vêm sido desenvolvidos para promover a redução dos gastos energéticos e a minimização dos efeitos das não-linearidades nestes sistemas. A aplicação da automação e do controle de processos, particularmente o uso de técnicas avançadas de controle, são estratégias amplamente utilizadas para esta finalidade. O Controle Preditivo baseado em Modelos (MPC) é capaz de estabilizar processos onde há não-linearidades, sendo promissora a sua aplicação em sistemas de refrigeração. Neste trabalho, foi desenvolvido um SIStema de MOnitoramento e Controle Avançado para Refrigeração (SISMOCAR) capaz de monitorar, em tempo real, através da comunicação OPC (OLE for Process Control), todas as variáveis envolvidas no ciclo de refrigeração e também realizar o controle das variáveis de interesse. Modelos Takagi-Sugeno (SISO) para a predição das temperaturas de evaporação (Te) e do fluido secundário (Tp) foram desenvolvidos e validados, a partir da técnica ANFIS (Adaptative Network based Fuzzy Inference Systems), com análise de desempenho baseado no cálculo do VAF (Variance accounted for). Os modelos Takagi-Sugeno validados foram utilizados como base para Controladores Preditivos, mais especificamente um Controlador Preditivo Generalizado (GPC). Os controladores GPC's foram desenvolvidos sem restrições na função objetivo da ação do controlador. Foram projetados diferentes controladores preditivos para diferentes regras locais (Regras Fuzzy), sendo a ação global do controlador a integração ponderada dos modelos locais. Foram desenvolvidos três diferentes controladores: GPC1 (controle da temperatura de evaporação utilizando modelo de predição da Te em função da frequência do compressor); GPC2 (controle da temperatura do propilenoglicol utilizando modelo de predição da Tp em função da frequência do compressor) e GPC3 (controle da temperatura do propilenoglicol utilizando o modelo de predição da Tp em função da frequência da bomba do evaporador). Os testes realizados para rastreamento do set-point (±1 °C), com carga térmica constante de 3000 W, mostraram-se satisfatórios sendo os melhores desempenhos apresentados pelos controladores GPC1 e GPC2 onde o desvio da variável controlada em relação ao set point, dos respectivos controladores, ficou em torno de ± 0,3 °C
Abstract: Refrigeration systems can be found in many different branches of industry and are characterized as great energy consumers with considerable non-linear behavior. Several studies have been developed to promote the reduction of energy costs and to minimize the effects of nonlinearities in these systems. The use of automation and process control, particularly the use of advanced control techniques, is a widely used strategy for this purpose. The Model Predictive Control (MPC) is capable of stabilizing processes in which there are nonlinearities, and it is a promising application in refrigeration systems. In this work, a System for Monitoring and Advanced Control in Refrigeration (SISMOCAR) was developed using OPC (OLE for Process Control) communication. This feature allowed beyond real time monitoring for all variables involved in the refrigeration cycle, the control of the relevant variables. Furthermore, to predict the evaporating (Te) and the secondary fluid (Tp) temperatures, Takagi-Sugeno models (SISO) were developed and validated using the ANFIS (Adaptive Network-based Fuzzy Inference Systems) technique, with performance analysis based on the VAF (Variance accounted for) calculation. The validated Takagi-Sugeno models were used as basis for Predictive Controllers, specifically using Generalized Predictive Controller (GPC) strategy. The GPC controllers were developed without constraints in the objective function of the controller action. Different predictive controllers were designed for different local rules (Fuzzy Rules), being the weighted integration of the local models the controller global action. Three different controllers were developed: GPC1 (evaporating temperature control using the Te predictive model as a function of compressor frequency); GPC2 (control of propylene glycol temperature using the Tp predictive model as a function of compressor frequency) and GPC3 (control of propylene glycol temperature using the Tp predictive model as a function of the frequency of the evaporator pump). The tests performed for the set-point tracking (± 1 °C), with constant thermal load of 3000 W, were considered satisfactory and best performances were those obtained by GPC1 and GPC2 controllers, in which the controlled variable was around ± 0,3 °C
Doutorado
Sistemas de Processos Quimicos e Informatica
Doutor em Engenharia Química

O presente trabalho teve como objetivo verificar a possibilidade de combinação de diferentes técnicas de pós-colheita em caquis cv. Giombo destanizados com álcool etílico, visando o aumento da conservação pós-colheita desses frutos através da manutenção da firmeza de polpa durante o armazenamento. Para tanto, aplicou-se o armazenamento refrigerado, associado à aplicação de 1-metilciclopropeno e destanização através de vapores de álcool etílico. No primeiro experimento os frutos foram acondicionados em câmaras de destanização, sendo submetidos à dosagem fixa de álcool etílico (3,50 mL Kg-1) durante 12 horas e a aplicação de uma dosagem fixa de 1000 nL L-1 de 1-metilciclopropeno (1-MCP) também durante 12 horas, sendo que a diferenciação entre os tratamentos foi obtida de acordo com o momento da destanização, da aplicação de 1-MCP e da combinação entre eles. Todos os frutos foram armazenados durante 30 dias sob refrigeração a 5 ± 1°C e 90 ± 5% UR e, posteriormente, em temperatura ambiente (25°C e 90 ± 5% UR) durante 15 dias. No segundo experimento, os frutos de caqui foram acondicionados em câmaras de destanização e submetidos aos mesmos processos do primeiro experimento. Os tratamentos foram obtidos através da combinação entre o momento da destanização e aplicação do 1-MCP e após serem submetidos aos tratamentos, sendo que a aplicação do 1-MCP foi realizada antes, durante ou após a destanização. Os frutos foram armazenados a temperatura ambiente (25 ± 1°C e 90 ± 5% UR) durante 15 dias. As determinações realizadas foram: firmeza de polpa, índice de adstringência, pH, teor de sólidos solúveis, teor de taninos solúveis, cor de casca e cor de polpa. As avaliações foram realizadas antes da aplicação dos tratamentos (caracterização do fruto), 1 dia após o tratamento e a cada 2 dias sucessivamente, durante 15 dias. No primeiro experimento os frutos tratados com 1-MCP e os frutos do controle apresentaram maior firmeza de polpa no final do período de análises em relação aqueles tratados apenas com etanol. Em contrapartida, os frutos que foram submetidos ao etanol apresentaram rápida perda de adstringência enquanto os frutos não tratados e aqueles tratados apenas com 1-MCP se mantiveram adstringentes durante os 15 dias de análises. No segundo experimento, resultados semelhantes aos do primeiro experimento foram obtidos em relação à diminuição da adstringência, com a ressalva de que essa diminuição ocorreu mais lentamente. Em relação à firmeza de polpa dos frutos poucas diferenças foram observadas até o final do período de armazenamento, quando os frutos tratados com 1-MCP se mostraram um pouco mais firmes que os outros. A aplicação de 1-MCP (1000 nL L-1) não interfere na remoção de adstringência com etanol em caquis Giombo armazenados sob refrigeração e a temperatura ambiente, além de permitir a manutenção da firmeza dos frutos. O 1-MCP, quando aplicado isoladamente, retarda o amadurecimento e a remoção natural da adstringência.
The present work had aimed to verify the possibility of combine different postharvest techniques in Giombo persimmon, submitted to astringency removal process with ethyl alcohol, aiming to enhance de postharvest conservation of these fruits trough the maintenance of flesh firmness during storage. To achieve this, different kinds of technologies already in use in postharvest of vegetables products, as cold storage, application of 1-methylcyclopropene and astringency removal using ethyl alcohol, were combined. In a first experiment persimmon were packed in astringency removal chambers, being undertaken to an unchanged dose of ethyl alcohol (3.50 mL Kg-1) during 12 hours and to an application of an unchanged dose of 1,000 nL L-1 of 1- methylcyclopropene (1-MCP) also during 12 hours. The differentiation between treatments was obtained according to the moment of astringency removal process, of 1- MCP application and the combination among them. All fruit were stored during 30 days under refrigeration at 5 ± 1°C e 90 ± 5% RH and after this period the fruits were stored at room temperatures (25°C and 90 ± 5% RH) during 15 days. In the second experiment, as in the previous experiment, fruit were packed in astringency removal chambers and were undertaken to the same procedures already described above, being utilized the same dosages. The treatments were obtained according the moment of astringency removal process and 1-MCP application, being that the 1-MCP application were made before, during or after the astringency removal process. After being undertaken to the treatments, fruit were stored at room temperature (25 ± 1°C and 90 ± 5% RH) during 15 days. The parameters analyzed were pulp firmness, astringency index, pH, soluble solids content, soluble tannins content, peel color and pulp color. The evaluation was performed before treatments application (fruit characterization), at the first day after treatments application and then every other day during 15 days. In the first experiment fruits treated with 1-MCP and fruit from control presented higher flesh firmness at the end of analyses period in relation to those treated only with ethanol. However, fruit undertaken to ethanol presented quick astringency loss while not treated fruits and fruits treated only with 1-MCP maintained astringency during the 15 days of analyses. In the second experiment, the results obtained were similar to those of the first experiment in relation to astringency losses, but in this experiment, astringency loss took a few more days to happen. In relation to fruit flesh firmness few differences were observed until the end of storage period, when fruit treated with 1-MCP were a little firmer than the others. The application of 1-MCP (1,000 nL L-1) does not interfere on ethanol astringency removal of Giombo persimmons previously stored in cold temperatures or not and it decelerate firmness losses on these fruits. The 1-MCP, when applied alone, slows ripening and natural astringency loss.

Die Erfindung der Kältemaschine macht es möglich, dass heute zu beliebiger Zeit Kälte in benötigter Menge und gewünschter Temperatur erzeugt werden kann. Aber für die Kälteerzeugung braucht man Antriebsenergie. Das Ziel dieser Doktorarbeit besteht darin, mit einer intelligenten Kombination von thermostatischem Expansionsventil (TEV) und innerem Wärmeübertrager (IWÜ) den Energieverbrauch von Kälteanlagen deutlich zu verringern, ohne dass dies zu einer Verschlechterung der Zuverlässigkeit oder wesentlichen Mehrkosten führt. Bis heute gelten die beiden bekannten Komponenten TEV und IWÜ als inkompatibel miteinander, weil die einfache Aneinanderreihung zu einem instabilen Regelverhalten führt. Nach detaillierter Analyse der Ursachen dieser Instabilität wird die Hypothese aufgestellt, dass durch eine absichtliche „Verschlechterung“ des IWÜ ein stabiler Arbeitsbereich gefunden werden kann. Bei dieser „Verschlechterung“ kann es sich z. B. um den Bypass eines Teils des Hochdruckstromes oder um eine Gleichstromanordnung der Ströme im Wärmeübertrager handeln. Diese Hypothese wurde primär durch Experimente, aber zusätzlich auch durch Simulationsrechnungen bestätigt. Dafür wurde ein Versuchsstand aufgebaut, mit welchem verschiedene Konfigurationen und Regelstrategien getestet wurden. Es wurde eine deutliche Verringerung des Energieverbrauchs gegenüber herkömmlichen Anordnungen erreicht.

Die Erfindung der Kältemaschine macht es möglich, dass heute zu beliebiger Zeit Kälte in benötigter Menge und gewünschter Temperatur erzeugt werden kann. Aber für die Kälteerzeugung braucht man Antriebsenergie. Das Ziel dieser Doktorarbeit besteht darin, mit einer intelligenten Kombination von thermostatischem Expansionsventil (TEV) und innerem Wärmeübertrager (IWÜ) den Energieverbrauch von Kälteanlagen deutlich zu verringern, ohne dass dies zu einer Verschlechterung der Zuverlässigkeit oder wesentlichen Mehrkosten führt. Bis heute gelten die beiden bekannten Komponenten TEV und IWÜ als inkompatibel miteinander, weil die einfache Aneinanderreihung zu einem instabilen Regelverhalten führt. Nach detaillierter Analyse der Ursachen dieser Instabilität wird die Hypothese aufgestellt, dass durch eine absichtliche „Verschlechterung“ des IWÜ ein stabiler Arbeitsbereich gefunden werden kann. Bei dieser „Verschlechterung“ kann es sich z. B. um den Bypass eines Teils des Hochdruckstromes oder um eine Gleichstromanordnung der Ströme im Wärmeübertrager handeln. Diese Hypothese wurde primär durch Experimente, aber zusätzlich auch durch Simulationsrechnungen bestätigt. Dafür wurde ein Versuchsstand aufgebaut, mit welchem verschiedene Konfigurationen und Regelstrategien getestet wurden. Es wurde eine deutliche Verringerung des Energieverbrauchs gegenüber herkömmlichen Anordnungen erreicht.

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Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - CAPES
The present paper describes an theoretical-experimental study of an double effect absorption refrigeration machine in series that uses the waste heat from the exhaust fumes of an internal combustion engine as an energy source for the steam generator. Stress that the machine being used was designed and built on the premises of the Federal University of Paraíba in the Institute of Sustainable Energy and recog-IES laboratory, Cooperative Research Network North / Northeast Natural Gas. This study aims to describe the constructive aspects of a pilot plant with cooling capacity of around 0.5 TR, emphasizing discussion relation to the accuracy, errors, difficulties, problems identified and solutions found during the construction processes, testing, operation, data acquisition and evaluation of the pilot plant.
O presente trabalho descreve um estudo teórico-experimental de uma máquina de refrigeração por absorção de duplo efeito em série usando o par água brometo de lítio e que utiliza o rejeito de calor proveniente dos gases de escapamento de um motor de combustão interna como fonte energética para o gerador de vapor de vapor de alta. A máquina está sendo desenvolvida nas próprias instalações da Universidade Federal da Paraíba no laboratório do Instituto de Energia Sustentável IES e RECOGÀS, Rede Cooperativa de Pesquisa Norte/Nordeste de Gás Natural. Este estudo visa descrever os aspectos construtivos de uma unidade piloto com capacidade frigorífica em torno de 0,5 TR, dando ênfase a discussões em relação aos acertos, erros, dificuldades obtidas, problemas identificados e soluções encontradas durante os processos de construção, testes, funcionamento, aquisição de dados e avaliação da unidade piloto. É feito também uma comparação dos dados experimentais com os resultados obtidos de um modelo termodinâmico baseado nos conceitos de energia e exergia. O código computacional é desenvolvido em plataforma EES (Engineering Equation Solver), aproveitando a facilidade de obtenção das propriedades, sobretudo, da solução água brometo de lítio.

Une grande partie de la consommation d'énergie dans les bâtiments est due aux systèmes de chauffage, de ventilation et de climatisation. Entre autres systèmes, les systèmes de réfrigération font l'objet de mesures d'amélioration de l'efficacité. Néanmoins, les conditions opérationnelles réelles de ces installations et leurs performances doivent être connues, ainsi que tout potentiel d'optimisation éventuel, avant que des améliorations puissent être réalisées. Les analyses exergétique et énergétiques ont été largement utilisées pour évaluer la performance des systèmes de réfrigération. Entre autres, l'efficacité exergétique est utilisée comme indicateur pour déterminer la performance du système, mais les valeurs réalisables dans la pratique sont inconnues. Par conséquence, ce travail propose une méthode d'évaluation pratique des systèmes de réfrigération basée sur une analyse exergétique et des normes techniques comme base de référence. L'identification des améliorations possibles est pertinente dans la pratique, car les mesures qui améliorent l'efficacité du système permettent probablement d'éviter de fréquentes déficiences pendant l'usage. Avec l'optimization potential index (OPI) introduit dans cet ouvrage, les améliorations réalisables par rapport à l'état de l'art de la technologie et la performance sont identifiées d'un seul coup d’œil, quelle que soit la complexité du système. En divisant l'installation en sous-systèmes, chacun peut être évalué individuellement. Les non-spécialistes peuvent facilement déterminer l'état de fonctionnement du système et ensuite, si nécessaire, lancer une analyse détaillée ainsi que des contre-mesures appropriées. De plus, la modélisation est considérée comme une méthode appropriée pour déterminer des valeurs de référence. Parmi les différentes techniques, les modèles artificial neural network révèlent les meilleures performances pour l'application présentée. L'application, la fonctionnalité et l'objectif de la méthode présentée sont illustrés par deux cas numériques et sur une installation réelle. La recherche révèle un fonctionnement approprié de l'installation étudiée en général, où trois des sept espaces conditionnés ont des problèmes de performance. La raison devrait être identifiée dans une étude détaillée ultérieure. Dans l'ensemble, l'apport d'exergie électrique auxiliaire est du même ordre que l'apport d'exergie thermique. Cela souligne l'importance de réduire la consommation d'énergie électrique au minimum, car elle constitue le facteur principal dans le coût d'exploitation des installations de réfrigération et permet également d'augmenter la performance du système. En outre, les concepts de mesure des systèmes réels sont analysés et les coûts de mise à jour correspondants pour l'application de l'approche présentée sont identifiés. Il est démontré qu'une mise à jour de l'instrumentation peut être rentable, si l'installation frigorifique comprend déjà un concept de mesure proche de l'état de la art
A significant amount of energy consumption in buildings is due to heating, ventilation and air-conditioning systems. Among other systems, refrigeration plants are subject of efficiency improvements. However, actual operating conditions of such plants and the performance must be known as well as any eventual optimization potential identified before enhancements can take place. Energy and exergy analyses have been widely used to assess the performance of refrigeration systems. Among others, exergy efficiency is used as an indicator to determine the system performance; however, the practical achievable values are unknown. Therefore, this work proposes a practice-oriented evaluation method for refrigeration plants, based on exergy analysis and technical standards as baseline. The identification of possible enhancements is highly relevant in practice, as measures which improve the system effectiveness most likely prevent frequent shortcomings during refrigeration plant operation. With the introduced optimization potential index (OPI), the achievable enhancements compared to the state of the art in technology and the performance are identified at a glance regardless the complexity of the system. By dividing the plant into different subsystems, each of them can be assessed individually. Laypersons can easily determine the system operating state and subsequently, if needed, initiate a detailed analysis as well as appropriate countermeasures by specialist. Moreover, modeling is seen as an appropriate method to determine additional reference values for refrigeration machines if none are available according to technical standards. Among different modeling techniques, artificial neural network models reveal the best performance for the present application. The application, functionality and purpose of the presented method is exemplified on two numerical test cases and on a real field plant as a case study. The investigation reveals an adequate operation of the studied field plant in general, where three out of seven cooling locations have performance issues. The reason should be identified in a subsequent detailed study. Overall, the auxiliary electrical exergy input shows the same magnitude as the thermal exergy input. This emphasizes the importance of minimizing the electrical energy usage, as it is the main overhead in the operating cost of refrigeration plants and also to achieve an increase in system performance. Moreover, measuring concepts of real systems are analyzed and the corresponding retrofitting costs for the application of the presented approach are identified. It is shown that a retrofit of the instrumentation can be worthwhile if the refrigeration plant already comprises a measuring concept close to the state of the art

Thesis (PhD)--Stellenbosch University, 2004.
ENGLISH ABSTRACT: During the last 30 years I have been involved in the theory and practice of thermal engineering and in particular, in the areas of air-cooled heat exchangers and cooling towers for the power, refrigeration, process and petrochemical industries in South Africa and internationally. During this period, I have authored and co-authored more than 120 papers that were published in technical journals or presented at conferences nationally or internationally. Most of these papers are included in a manuscript entitled "Air-cooled Heat Exchangers and Cooling Towers", in which Ipresent a systematic approach to the thermal performance evaluation and design of industrial air-cooled heat exchangers and cooling towers. This original publication also includes the relevant practice applicable to the design of cooling systems, based on my experience as a consultant to industry. Design offices throughout the world presently follow our design methods, or at least employ many of our research results. Our work has furthermore contributed to the development of improved cooling system designs (e.g. new dephlegmator header designs), components (e.g. single-row flattened finned tubes) and product improvement and quality control (e.g. performance testing and measurement of thermal contact resistance between fin and tube during production). Many of our research findings have found application in the modification of existing cooling systems. The manuscript has also been used as reference work during the presentation of short courses to practising engineers and consultants in industry and to engineering graduates at the University of Stellenbosch. A two-volume edition of this manuscript was published by PennWell Corp., Tulsa, Oklahoma, USA in 2004.
AFRIKAANSE OPSOMMING: Gedurende die laaste 30 jaar was ek betrokke by die teorie en praktyk van lugverkoelde warmteoordraers en koeltorings vir die kragopwekkings-, verkoelings-, proses- en petro-chemiesenywerhede in Suid-Afrika sowel as in die buiteland. Gedurende hierdie periode was ek outeur en mede-outeur van meer as 120 publikasies wat in tegniese tydskrifte, of by plaaslike of oorsese konferensies aangebied is. Die meeste van hierdie publikasies vorm deel van 'n manuskrip getiteld "Air-cooled Heat Exchangers and Cooling Towers" waarin ek 'n sistematiese benadering tot die bepaling van die termiese vermoë en ontwerp van industriële lugverkoelde warmteoordraers en koeltorings aanbied. Hierdie oorspronklike publikasie bevat ook die relevante praktyk wat van toepassing is op verkoelingsaanlegte. Ontwerpkantore wêreldwyd volg tans hierdie ontwerpsmetodes, of gebruik ten minste baie van ons navorsingsresultate. Ons werk het verder bygedra tot die ontwikkeling van verbeterde verkoelingsaanlegte (bv. nuwe deflegmatore), komponente (bv. enkelbuisry platvinbuise ) en verbeterde produkte en kwaliteitskontrole (bv. toetsing van verkoelingsvermoë oftermiese kontakweerstand tussen vin en buis gedurende produksie). Baie van ons bevindinge het toepassing gevind in die modifikasie van verkoelingsaanlegte. Die manuskrip is ook as verwysing gebruik gedurende die aanbieding van kort kursusse aan ingenieurs in die praktyk en aan nagraadse studente aan die Universiteit van Stellenbosch. 'n Twee-volume uitgawe van die manuskrip is deur PennWell Corp., Tulsa, Oklahome, VSA in 2004 gepubliseer.

This study describes the development and use of a mathematical model that will enable mine operators to minimise the costs of electricity consumed by the ventilation and refrigeration systems used for environmental control in deep mines. This model was calibrated and tested by using actual data from a gold mine near Welkom in South Africa. In a first simulation, the mine's current practice of controlling conditions to a wet bulb temperature (Twb) of 25S°C, was optimised. The model demonstrated that this environmental condition could be sustained at lower electricity consumption. In so doing, the mine realised a saving of 30 000 kWh per day. The energy saving and load management led to a cost saving of R 1.5 million per year. However, a better indicator of environmental conditions is the Air Cooling Power index, (ACP). Research has shown that for hard physical work in hot conditions workers need an ACP of 300 w/m2. It was found that the case study mine actually supplied their workplace with a cooling capacity of 422 w/m2. The new model optimised the refrigeration and ventilation systems in such a manner that the workers were supplied with exactly 300 w/m2, no more and no less. It was found that by doing this, an electricity saving of 57 600 kWh per day could be realised when compared with the current mine practices. The energy saving and load management led to a potential cost saving of R 2.55 million per year. (Certain capital costs, such as for variable speed drives may have to be incurred to realise these savings.) The new model could be further extended to take advantage of the new Real Time Price offerings from Eskom It will be able to identify an operating point for the refrigeration and ventilation systems to supply 300 w/m2 for the workers, in real time, at the lowest electricity cost.
Thesis (Ph.D. (Mechanical Engineering))--North-West University, Potchefstroom Campus, 2004.

Mestrado em Gestão e Estratégia Industrial
O estudo concentra-se na análise comparativa entre o desenvolvimento de obras ditas tradicionais e o desenvolvimento de obras com a aplicação dos valores e ferramentas organizativas baseadas do paradigma Kaizen. No sentido de que o paradigma é um lugar-comum para a difusão de valores integradores, focalizados para os desígnios estratégicos ao longo de toda a hierarquia das estruturas, dinâmico na inovação das melhores práticas, orientado para o cliente, questionando incessantemente todos os aspectos técnicos e organizativos, sempre numa perspectiva de melhoria contínua, considera-se que a observação, o acompanhamento e a avaliação constante da aplicação do modelo constitui um aspecto basilar de todo o conceito. Assim, o estudo documenta o acompanhamento diário da obra, salientando os pontos fortes e fracos da aplicação do modelo comparativamente ao modelo tradicional, traçando os aspectos particulares da adaptação, sob o ponto de vista de uma empresa fornecedora de equipamentos e serviços técnicos. Culmina-se na conclusão atingida, tanto em termos quantitativos como em termos qualitativos, que a taxa de sucesso está intrinsecamente relacionada com o acompanhamento constante com grande carácter de proximidade, de todo o processo de implementação da filosofia Kaizen. Em linha com a nova realidade, conclui-se igualmente que a conjuntura actual obriga à reformulação da filosofia de operação da empresa fornecedora de equipamentos e serviços, adequando-se ao modelo organizativo do seu maior cliente, sob prejuízo da degradação das relações comerciais
This study focuses on the comparative analysis between the development of so-called traditional construction works and development of construction works with the application of values-based organizational tools of the Kaizen paradigm. In the sense that the paradigm is a common place for the dissemination of integrating values, focused for strategic purposes over the entire structure hierarchy, dynamic in the innovation best practices, customer-oriented, constantly questioning all the technical and organizational aspects, always with a view to continuous improvement, it is considered that the observation, monitoring and constant evaluation of the implementation of the model is a fundamental aspect of the whole concept. Thus, the study documents the daily monitoring of the construction work, highlighting the strengths and weaknesses of the model application compared to the traditional model, outlining the particular aspects of adaptation, from the viewpoint of a supplier of equipment and technical services. Culminates in the conclusion reached in both quantitative as in qualitative terms that the success rate is intrinsically related to the constant monitoring with great character of proximity of the whole process of implementation of the Kaizen philosophy. In line with the new reality, it also concludes that the current situation requires the reformulation of the equipment and services supplier operation philosophy, adapting to the organizational model of its biggest customer, at the expense of deterioration of commercial relations.

Artificial ground freezing (AGF) is a process used to strengthen soil and rock by freezing trapped pore water. Freezing is accomplished by pumping calcium chloride brine, chilled to approximately – 30˚C in ammonia refrigeration plants, through heat exchangers drilled into the ground. A knowledge gap exists in the field of AGF regarding the relationship between the performance of the refrigeration plants and the ground heat removal process. The coupling of these two aspects of AGF requires knowledge of the plant’s refrigeration capacity as a function of many factors; the most important of which is the temperature of the brine returning from the freeze pipes. However, refrigeration plant manufacturers do not provide sufficient information about the plant’s performance as a function of brine temperature. Typically, AGF plants are only rated at one operating point due to the impracticality in experimentally rating such large plants and the lack of any standard test methods. Refrigeration system models available in the existing literature do not emulate the compressor control system responsible for preventing compressor overloading. Therefore, the goal of this research is to develop a model that can predict the performance of an AGF refrigeration plant over a range of operating points, using plant specifications that are readily available in the documentation provided by the manufacturer of the plant. To fill the knowledge gap, a thermodynamic model is developed of an existing 1500 TR AGF plant at Cameco’s Cigar Lake mine. The Cigar Lake plant uses flooded shell-and-tube evaporators, two-stage economized twin screw compressors, and air cooled condensers packaged into five refrigeration modules. Each component in the system, including the evaporator, compressor, and condenser, is modeled individually, and then the individual models are combined to calculate the overall system capacity. The model emulates the behavior of the compressor’s slide valves, which are used to limit the plant capacity, limit suction pressure, control intermediate pressure, and control the discharge pressures in the system. In addition, the model accounts for the effects of the oil injection into the screw compressors, which cools the compressors and seals the spaces between the lobes of the compressor rotors. The model is validated using operating data from the Cigar Lake plant, which was collected over a period of eight months by plant operators. After calibration, the modeled plant capacities and the temperature of the brine leaving the refrigeration plant are found to be in agreement with the measured capacities and brine temperatures. The overall plant capacity results match measured capacities within ±14%, and the predicted brine temperatures match the measured values leaving the plant within ±5%. The modeled capacities match the measured capacities within the uncertainty in the measured data. The simulation of the Cigar Lake plant demonstrates that the performance of the plant is highly dependent upon the temperature of the brine returning to the plant. For example, a ±10% change in brine temperature causes a 22% overall change in the capacity of the refrigeration plant. The simulation also demonstrates that, even with the plant’s air cooled condensers, changes in the ambient temperature have little effect on the performance of the plant with the existing equipment. Furthermore, the results show that the selected suction pressure of the second compression stage, or intermediate pressure, affects the performance of the refrigeration plant. These findings lead to important plant performance optimization opportunities. An optimization study using the model demonstrates that, by selecting a lower intermediate temperature than what the existing literature suggests, an improvement in overall refrigeration plant capacity of 3% can be achieved. Additional simulations identify the brine tank, which allows for different brine flow rates to exist on the field and plant side of the tank, as an inefficient component in the system. The brine tank not only cools the brine returning from the field before it is pumped to the refrigeration modules but it allows heat to be transferred between the warm and cold brine. By eliminating the tank, plumbing all of the refrigeration modules in parallel, and installing appropriately sized evaporators, the capacity of the refrigeration plant can be increased by 17%. Further capacity gains can be realized by upgrading the evaporators to increase their capacity.