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Made available in DSpace on 2014-06-11T19:30:09Z (GMT). No. of bitstreams: 0 Previous issue date: 2012-01-04Bitstream added on 2014-06-13T18:40:00Z : No. of bitstreams: 1 tassini_jo_me_guara.pdf: 1303049 bytes, checksum: 305724b8b2b6efcf44bbdd121e531009 (MD5) / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / Em alguns tipos de indústria, como por exemplo a de laticínios, bebidas e frigoríficos, o sistema de refrigeração é responsável por uma parcela significativa no consumo de energia elétrica. Tendo como objetivo a redução deste consumo, foi realizado um estudo de caso em uma indústria produtora de bebidas, sendo analisados todos os componentes do sistema de refrigeração. O sistema de refrigeração analisado utiliza amônia anidra (NH3) como fluido refrigerante no circuito principal e solução de etanol no circuito secundário, sendo composto por compressores do tipo parafuso, condensadores evaporativos, evaporadores de placas, conjunto de bombas e válvulas expansoras com controle eletrônico. Usualmente, os sistemas de refrigeração atendem diversos processos e etapas de produção, que diferem nos requisitos de temperatura de produto. Além disso, por serem projetados para atender a maior demanda esperada, constituem uma grande oportunidade de otimização nos períodos fora de pico de consumo. Foram descritos e detalhados os componentes do sistema de refrigeração, bem como todas as ações e requisitos necessários para melhoria na eficiência energética da instalação. A implementação destas ações de melhoria de eficiência na planta industrial estudada contou com um investimento total de R$ 302.000,00, e foram responsáveis por um ganho anual de R$ 241.000,00, correspondentes a uma redução no consumo elétrico de 1,7 GWh/ano. O payback simples, portanto, é de 1,25 anos / In some types of industry where cooling systems are required, for example, dairy products, beverages and frozen foods, the cooling system is responsible for a significant portion of electricity consumption. Aiming to reduce this consumption, a case study was performed in a beverage industry, and all the refrigeration systems components were analyzed. The cooling system operates using anhydrous ammonia (NH3) as the refrigerant in the main circuit and ethanol solution in the secondary circuit, it consists of screw compressors, evaporative condensers, plate and frame coolers, pumps and expansion valves with electronic control. Usually, refrigeration systems have several processes and production stages to meet for different products, depending on the products temperature requirements. Moreover, they are designed to attain the highest demand expected, which gives a great opportunity to optimize the off-peak periods of consumption. We have described and itemized whole refrigeration systems components, as well as all actions and requirements to improve the energy efficiency of the installation. The energy efficiency improvements actions that were implemented in this industrial plant study had a total investment of R$ 302,000.00. These improvementes resulted in an annual saving of R$ 241,000.00, as well a relative a reduction in electricity consumption of 1,7 GWh/year. Therefore, the simple payback is 1.25 years

A mathematical model which predicts the cooling system performance for a rally car is derived in this study. A case study vehicle was made available by a local manufacturer for evaluation of the cooling system. Two heat exchangers compatible for the vehicle were tested in a controlled wind tunnel environment to determine its heat transfer characteristics. Including the relationship between fluid flows and vehicle speed, a function resulted through which the cooling system performance can be predicted. Including the heat generated by the engine to be dissipated by the cooling system and the effect of ambient conditions on heat generated and dissipated, an energy balance results. Using the energy balance a contour plot is generated which predicts the suitability of the heat exchanger at various ambient conditions. The tool thus allows the user to assess the cooling system on the day of the race, highlighting whether the required cooling will be achieved. / Dissertation (MEng(Mechanical))--University of Pretoria, 2007. / Mechanical and Aeronautical Engineering / unrestricted

The simulation of vehicle engine cooling validation in a Climatic chamber will benefit all vehicle manufacturers that are responsible for the design or the localization of parts used in a vehicle's engine cooling system. The ability to test the vehicle in-house allows testing at any time of the year; it provides repeatable and comparative data, and accelerates component level approval, which in itself reduces program timing and cost. For this dissertation road level testing was conducted in Upington using a TD1200 Superflow towing dynamometer, while the in-house testing was performed on a ROTOTEST chassis dynamometer in a Climatic chamber. All tests were conducted according to GENERAL MOTORS SOUTH AFRICA global testing standards. Statistical analyses of the test data were used to determine the relationship between parameters measured and results obtained. The major contributors to the simulation process was identified and implemented to improve measurement quality and test results. The result was an accurate simulation between road and chamber testing, hence the possibility of moving away from road testing and conduct simulated chamber testing. The presented dissertation is useful for the understanding of basic vehicle cooling testing and the methodology of simulated testing in an environmentally controlled chamber.

The spray cooling system of an operating billet caster has been redesigned with the aim of reducing the formation of mid-way cracks. These cracks are caused by tensile strain which is generated at the solidification front when the surface temperature of the strand rebounds owing to a sharp reduction in surface heat extraction. The objective of the design, therefore, was to achieve a cooling system that would minimize surface temperature rebound of the strand as it passes from one cooling zone to the next. A computer program based on the explicit finite difference method has been used for the design work. The spray design was implemented on one strand of an operating continuous casting machine which produced 10.8 cm square billets. Transverse sections were cut from the test strand and sulfur printed, then compared to sulfur prints of sections taken from an adjacent strand of the same heat but with unmodified sprays. It was shown that with empirical adjustment, the redesigned spray system reduced the severity of mid-way cracks in over 80% of the heats. It was also found that the carbon content and cast structure have a profound effect on the cracking tendency, whereas, the Mn/S ratio (up to 30%) is less effective. Finally, a new design method for sprays has been proposed which may result in a better temperature distribution and may be easier to adjust to suit specific operating conditions. / Applied Science, Faculty of / Materials Engineering, Department of / Graduate

Surveillance of countries' borders is of greatest interest to monitor to detect enemies. Saab's radar aircraft has air, ground and sea surveillance capabilities and is characterized by the large radar that attaches to the fuselage of the aircraft. When designing future aircraft and unmanned vehicles, weight and energy efficiency are sensitive parameters to consider. The weight of aircraft and its equipment has an important impact on, among other things, fuel consumption and thus how long they can stay in the air. In addition, all mission equipment must be provided with cooling to avoid overheating. The aim of this study has been to analyze and evaluate existing refrigeration systems in some of Saab's radar aircraft during various operational scenarios and also review alternative designs for future vehicles and carbon dioxide as future cooling media. The refrigeration systems Environmental Control System and Mission Air Cooling System ensure that cabin and cockpit areas are tempered and pressurized and that all heat generated in the equipment is transported away and out to the surrounding atmosphere as a heat sink. The Environmental Control System uses ambient air as media. Compressed air is drained from engines or an auxiliary power unit and supplies the refrigeration system with air. The Mission Air Cooling System is a conventional refrigeration machine with R134a as the refrigerant. The existing cooling circuit absorbs heat in the evaporator which is placed in the air distribution where the air circulates and cools the equipment. The refrigerant then transports the heat to the surrounding atmosphere. Carbon dioxide as a refrigerant has been used since the 19th century. With the ongoing phasing out of conventional refrigerants, R134a included, carbon dioxide is starting to become relevant again. Despite carbon dioxide's good heat transfer properties, there is a major challenge regarding the high-pressure conditions, which places demands on the components of the refrigeration system. Carbon dioxide can reduce pressure losses and dimensions of components and pipelines as well as reduce installation weight. The performance of the refrigeration systems has been evaluated based on their coefficient of performance and how much energy from the engine corresponds to the amount of fuel that the refrigeration systems require. Pressure, temperature and enthalpy conditions were developed in a simulation program, alternatively previous calculation templates were reused to calculate heat transfers and work in each refrigeration system. In addition, the installation weights of the refrigeration systems in relation to each other were provided in order to be able to analyze these against other parameters, such as performance and complexity, for future aircraft and unmanned vehicles. An alternative construction in the Mission Air Cooling System was investigated where the air distribution is excluded and instead the cooling circuit is led all the way to the devices. The evaporator thus functions as a cooling plate. The calculations for a carbon dioxide machine were carried out using research articles. For the Environmental Control System, it turned out that the design of the air intake together with the air velocity profile in some cases generates low mass flows, which causes abnormal heat exchanges and temperature conditions in the cabin and cockpit. The Mission Air Cooling System had better performance in terms of coefficient of performance but has a long chain of energy conversions required for the electricity supply which contributes to energy losses. Calculations carried out for a carbon dioxide machine resulted in the compressor's displacement being able to be reduced by 89\%. Finally, based on the analyses and calculations carried out, a section is presented that explains which parameters should be considered for future designs for unmanned vehicles, as well as a figure that can be seen as an example of a system structure. The system structure is a conventional refrigeration machine with carbon dioxide as the refrigerant. Based on the analyses made regarding the installation weight and the performance of the refrigeration systems, it is likely that the presented system structure also contributes to the lowest weight and is an example of a refrigeration system in future aircraft and vehicles.

Made available in DSpace on 2014-10-09T12:53:58Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T14:09:27Z (GMT). No. of bitstreams: 0 / Tese (Doutoramento) / IPEN/T / Instituto de Pesquisas Energéticas e Nucleares - IPEN-CNEN/SP

Made available in DSpace on 2014-10-09T12:53:58Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T14:09:27Z (GMT). No. of bitstreams: 0 / A pesquisa e o desenvolvimento de sistemas passivos de resfriamento de emergência são necessários para os sistemas termo-nucleares de nova geração. Algumas informações fundamentais sobre a operação desses sistemas requerem a pesquisa de alguns processos relativos à circulação natural, principalmente em condições de escoamento bifásico envolvendo processos de condensação na presença não-condensáveis, pois muitas situações encontradas são novas. A bancada experimental de circulação natural (BCN) foi utilizada para a realização de testes com diversas concentrações de não-condensáveis e níveis de potência. O não-condensável presente no circuito diminui a taxa de transferência de calor para o secundário do trocador de calor, causando baixo desempenho do trocador de calor. A presença de altas concentrações de não-condensáveis no trocador de calor propicia elevadas variações de pressão, decorrentes do processo de condensação abrupto, determinando a inversão da vazão e de fortes vibrações e esforços nas tubulações do circuito. A concentração inicial de não-condensável e a geometria do circuito, na entrada do trocador de calor, determinam o estabelecimento de transitórios com escoamento bifásico. A BCN foi modelada com o código computacional de Análise de Acidentes e Termo-Hidráulica RELAP5/MOD3.3 e, os valores calculados foram comparados com os dados experimentais, apresentando boa concordância para menores concentrações de ar. Os valores calculados para maiores concentrações de não-condensável foram satisfatórios após o circuito ter atingido a temperatura de saturação no aquecedor elétrico. / Tese (Doutoramento) / IPEN/T / Instituto de Pesquisas Energéticas e Nucleares - IPEN-CNEN/SP

Mine cooling system components are an integral part of a mine‟s ventilation system. A mine‟s reliance on these capital intensive components are set to increase as mines deepen. Mine cooling systems consume up to a quarter of the electricity used on mines. Component efficiency should be monitored to ensure optimum utilisation. Downtime should be minimised so that production is not negatively influenced. Replacing expensive components in an age of severe economic pressure should be avoided altogether. In this study, the performance of mine cooling system components was monitored. The effects of various operational and maintenance interventions on component performance have been quantified. Quantifying the effects of management decisions led to the refining of operational procedures, the optimisation of future maintenance, and the subsequent identification of electrical energy savings potential without the need for expensive modifications. Investigations show that a mine could realise a saving of up to nine hundred thousand rand annually by optimising the maintenance schedule of chillers. Extrapolated results estimate an electrical energy saving of 52 127 MWh per year if the strategy were implemented on twenty of South Africa‟s biggest mines. In addition, a monetary saving in excess of five hundred thousand rand could be saved through refining operational procedures. These strategies will be possible without the need for expensive installations or complicated modifications. Monitoring cooling system performance allows management to identify trends in performance, to understand component inter-dependence, and to allow for informed decision-making. In addition, performance monitoring allows for the identification of component and instrumentation faults. Statistical control charts and simulation modelling are some of the tools that have been employed in this study. These tools assist management formulate strategies and decisions with a higher degree of confidence. / MIng (Mechanical Engineering), North-West University, Potchefstroom Campus, 2014