Thesis (MTech (Electrical Engineering))--Cape Peninsula University of Technology, 2018. / This research investigates the absorption spectra of rubidium and the feedback control of an external cavity diode laser. This research is a necessary prerequisite for laser (Doppler) cooling and trapping of rubidium atoms. Cooling rubidium atoms down to such low temperatures can be achieved using the Doppler cooling technique. Here a laser is tuned to remain resonant with a speci c atomic transition. To do this, the absorption spectra of rubidium must therefore be observed. All of the above require a reasonable knowledge about topics such as atomic physics, laser cooling and trapping, feedback control systems, and absorption spectroscopy. A discussion of these topics is provided. We have utilised an experimental setup which allowed for measurements of the Doppler broadened and Doppler free absorption spectra of rubidium, as well the analysis of the Zeeman e ect on the Doppler free spectra. The setup consisted of a saturated absorption spectrometer for high resolution spectroscopy and a Michelson interferometer for calibrating our measurements. In analysing the Zeeman e ect we added a set of Helmholtz coils to the saturated absorption spectroscopy arrangement to measure the splitting of the hyper ne energy levels. / French South African Institute of Technology (F'SATI) National Research Foundation

Lactobacillus acidophilus e Bifidobacterium lactis são microrganismos probióticos frequentemente utilizados em alimentos funcionais. No entanto, estes microrganismos devem resistir ao processamento, à estocagem do alimento, e sobreviver à passagem pelo trato-gastrointestinal, para chegarem ativos ao intestino e exercerem seus efeitos benéficos. Uma vez que os probióticos são sensíveis a uma série de fatores, tais como meio ácido, sais biliares e presença de oxigênio, a microencapsulação tem sido estudada com objetivo de protegê-los aos efeitos adversos do ambiente, além de promover a liberação controlada no local de ação do microrganismo, melhorando sua eficiência. Este trabalho teve como objetivo a produção e avaliação de micropartículas lipídicas contendo B. lactis ou L. acidophilus, produzidas por spray chilling, utilizando gorduras de baixo ponto de fusão, tais como gordura de palma e manteiga de cacau, como agente encapsulante. O diâmetro médio e a morfologia das partículas foram avaliados. Ensaios de sobrevivência foram conduzidos com objetivo de avaliar a resistência dos microrganismos ao processo encapsulação, resistência in vitro aos fluidos gástrico e intestinal simulados e estabilidade das células durante 90 dias de armazenamento a -18, 7 e 20 ou 37°C, dependendo da gordura utilizada. As micropartículasapresentaram-se em formato esféricoe com diâmetro médio que pode permitir o fácil escoamento no alimento, sem proporcionar impacto tecnológico negativo.A tecnologia de encapsulação por spray chilling, utilizando gordura de palma e manteiga de cacau, como agentes encapsulantes, proporcionou a obtenção de micropartículas eficientes na proteção dos probióticos frente ao processo de encapsulação e na manutenção da estabilidade das células quando estocados sob congelamento. Entretanto, aeficiência das micropartículas frente aos fluidos gastrointestinais e a estabilidade das células quando estocadas a 7 e 20 ou 37°C variaram de acordo com a gordura utilizada e com o microrganismo encapsulado. As micropartículas lipídicas obtidas são, portanto, uma matriz inovadora para a aplicação de probióticos, de baixo custo e com grande possibilidade de obtenção em escala industrial. O desafio futuro para o presente estudo é a seleção de um agente encapsulante que aumente a estabilidade das células, nas temperaturas ambiente e de refrigeração, a fim de aumentar as possibilidades de aplicação destas microcápsulas em produtos alimentícios. / L. acidophilus and Bifidobacterium lactis are probiotic microorganisms frequently used in food product. However they must remain viable during processing, entire shelf life of product and passing-through the gastrointestinal tract to provide beneficial effects on human health. Since theses microorganisms are sensitive to a series of factors, especially presence of oxygen and acid medium, microencapsulation has been studied as an alternative to increase probiotic cells viability and to provide the controlled release in the site of action, improving their efficiency. The aim of this study was to produce and evaluate lipid microparticles of L. acidophilus or B. lactis produced by spray chilling technology using low melting point fats, such as palm fat and cocoa butter, as the encapsulant agent. The mean diameter and morphology of the microparticles were evaluated. Survival assays were conducted to evaluate the resistance of the microorganisms to the spray chilling process, viability to the in vitro simulated gastric and intestinal fluids and viability during 90 days of storage at -18, 7 and 20/37°C, depending on the fat used. Microparticles presented a spherical shape and mean diameter that allows the flow of material in the food product without conferring technology influence. Spray chilling technology using fat palm or cocoa butter as the encapsulant agent was efficient in protecting the microorganism to the encapsulation process and 90 days of storage at -18°C. However the efficiency of the microparticles on the gastric and intestinal fluids and the cells stability during storage at 7 e 20 or 37°C varied according to the fat and microorganism used. The lipid microparticles seem to be a relatively innovative matrix for the application of probiotics with low costs and possibility of scale up. The future challenge in this study is to choose an encapsulant agent that improves cells resistance and viability at refrigerator and room temperatures to increase the possibility of application of these microcapsules in food products.

Orientador: Vivaldo Silveira Junior / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia de Alimentos / Made available in DSpace on 2018-08-24T19:17:01Z (GMT). No. of bitstreams: 1 Oliveira_CintiaCarlaMelgacode_M.pdf: 2012386 bytes, checksum: 17e9e513690eaa1341a66b69e6b22a64 (MD5) Previous issue date: 2014 / Resumo: A busca por equipamentos de refrigeração eficientes e acessíveis é crescente no mercado. Grandes empresas buscam instalar termoacumuladores, armazenamento de energia a baixa temperatura, em suas instalações por fatores econômicos. Com isso, este processo pode ser efetuado em horários fora de pico de energia e ser usado em horário de maior demanda energética, projetando-se então, equipamentos menores para acoplar ao sistema principal e melhorar o dimensionamento do espaço físico. Atualmente, um dos meios utilizado no sistema de resfriamento evaporativo é o uso de bomba de vácuo ou ejetores. Este trabalho tem como objetivo construir e avaliar energeticamente um sistema de resfriamento evaporativo com uso de ejetor, tendo água como fluido que circulará no seu interior, permitindo ser instalado em locais com abundância de água em circulação, perante a substituição ao sistema de resfriamento com uso de dispositivos mecânicos ou geradores. Ejetores são dispositivos usados para arrastar amostras por um jato de um fluido auxiliar, que constam essencialmente de um tubo aspirador e um bocal convergente, alimentando um compartimento convergente-divergente. Após a montagem mecânica e elétrica do sistema, estudou o comportamento do mesmo perante a mudança da vazão volumétrica e da temperatura da água de circulação, temperatura da água de reposição, presença de cavitação e avaliou o coeficiente de desempenho de acordo com as diferentes potências térmicas aplicadas no reservatório de resfriamento. O maior vácuo obtido no reservatório de resfriamento foi de 8,5 kPa nas condições operacionais nominais de 4,1 ± 0,1 m³/h e 5 ± 0,5 °C da água de circulação, atingindo 9,7 ± 0,5 °C a água de resfriamento. Não houve presença de cavitação no bocal do hidroejetor pois a pressão atingida no mesmo não foi inferior a pressão de saturação da água nas condições operacionais da água de circulação. A perturbação gerada, tipo pulso, no reservatório de resfriamento com a reposição da água de resfriamento em diferentes momentos de funcionamento do sistema, não resultou em mudanças expressivas quanto a desestabilidade do vácuo ou do aumento de temperatura no reservatório de resfriamento. O coeficiente de desempenho (COP), avaliado no sistema na maior inserção de potência térmica, 92,27 W pela água de resfriamento, foi de 0,077, sendo subestimado devido a possíveis problemas de eficiência da bomba. O sistema em estudo não foi ideal para resfriamento de fluido a baixas temperaturas nas condições operacionais estudadas, mas pode ser muito bom quando utilizado para resfriamento de fluido a patamares de temperatura maior, podendo ser complementar aos sistemas de refrigeração principal / Abstract: The search for efficient and affordable cooling equipment is increasing in the market. Big companies are always seeking to use thermal storage as a way to storage energy at low temperatures in their facilities due to economic factors. Therefore, this process can be done in off-peak energy periods and the energy stored can be used in times of high demand. This allows the design of smaller equipment, which can be coupled to the main system, improving the design of the physical space. Currently, evaporative cooling is conducted through the use of vacuum pumps or ejectors. This work aimed to construct and evaluate energy evaporative cooling system using an ejector, using water as the inner circulating fluid, which allows it to be installed in places plenty of water circulation, through the replacement of the cooling system using generators or mechanical devices by ejectors systems. Ejectors are devices used to drag samples by a jet of an auxiliary fluid, built essentially with a sniffer and a converging nozzle, which feeds a convergent-divergent compartment. After mechanical and electrical assembly of the system, the behavior of the system was evaluated by changing the volumetric flow rate and temperature of the circulation water, temperature of makeup water and cavitation water. The performance coefficient was also evaluated according to the different thermal inputs applied in the reservoir cooling. The higher vacuum obtained in the cooling tank was 8.5 kPa in a nominal volumetric flow rate of 4.1 ± 0.1 m³/h and circulating water at 5 ± 0.5 °C. In situation, the cooling water reached 9.7 ± 0.5 °C. There was no cavitation observed in hidroejector nozzle, since the pressure reached was not less than the saturation pressure of water in the operating conditions of the circulating water. The disturbance generated, like pulse, in the cooling reservoir with the replacement of the cooling water at different times, did not result in significant changes in vacuum destabilization or in the temperature rising in the cooling reservoir. The coefficient of performance (COP), evaluated at the greater inclusion of thermal power for cooling water (92.27 W) was 0.077. This value was underestimated due to problems of pump efficiency. The system studied was not ideal for cooling fluids at low temperatures the studied operating conditions, but it can be good enough when used for cooling fluids with higher temperatures, which may be complementary to the main refrigeration systems / Mestrado / Engenharia de Alimentos / Mestra em Engenharia de Alimentos

Orientador: Roger Josef Zemp / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Química / Made available in DSpace on 2018-08-25T15:18:44Z (GMT). No. of bitstreams: 1 Silva_IgorMacieldeOliveirae_M.pdf: 2922871 bytes, checksum: 4b7ffbcbf31e3be71d4453d00d6c7592 (MD5) Previous issue date: 2014 / Resumo: Sistemas de água de resfriamento são o método mais comum de rejeição de calor na indústria. Sistemas convencionais de água de resfriamento recirculante possuem uma rede de trocadores de calor em uma configuração paralela, demandando grande quantidade de circulação de água e torres de resfriamento. Embora a reutilização de água de resfriamento reduza a quantidade de água que é necessária no sistema e aumente o desempenho e capacidade da torre de resfriamento, a queda de pressão na rede de trocadores de calor pode aumentar devido ao seu arranjo em série-paralelo. Este estudo introduz uma metodologia para projetar diferentes sistemas de água de resfriamento e para analisar os impactos da reutilização de água sobre a queda de pressão na rede de trocadores de calor e sobre a torre de resfriamento. A partir de um modelo de super-estrutura, utiliza-se um algoritmo combinatorial com o auxílio da ferramenta de otimização Solver do Microsoft Excel para resolver um problema não-linear (NLP) de cada estrutura de rede de trocadores de calor. A queda de pressão em redes de trocadores de calor é avaliada por uma metodologia baseada na Teoria dos Grafos e utiliza os algoritmos de ordenação por topologia e de caminho crítico. Utiliza-se o método de Merkel para modelar a altura de uma torre de resfriamento e poder avaliar o volume necessário de uma torre de resfriamento para cada rede de trocadores de calor. Um estudo de caso é utilizado para ilustrar cada passo a medida que a metodologia é desenvolvida, buscando prover fundamentos para um estágio conceitual durante o projeto de um sistema de água de resfriamento / Abstract: Cooling water systems are the most common method of waste heat disposal in industry. Conventional recirculating cooling water systems have a heat exchanger network in a parallel arrangement, demanding not only substantial cooling water flow, but also large cooling towers. Although cooling water reuse reduces the amount of water that is recirculated in the system, thereby increasing the cooling tower capacity and performance, the pressure drop in the heat exchanger network may significantly increase due to series-parallel arrangements. This study introduces a methodology to design different cooling water systems and to analyse the cooling water reuse impacts on the heat exchanger network pressure drop and on the cooling tower size. From a superstructure model, a combinatorial algorithm in conjunction with the optimisation tool Solver in Microsoft Excel is used to solve a non-linear problem for each heat exchanger network structure. Pressure drop in heat exchanger networks is evaluated by a methodology that is based on Graph Theory and that uses topological sorting and critical path algorithms. Merkel's method is used to model the cooling tower height and to assess the required cooling tower volume for each heat exchanger network. A case study is used to illustrate each step as the methodology is developed, aiming to provide a basis for a conceptual stage during the cooling water system design / Mestrado / Engenharia Química / Mestre em Engenharia Química

The sample used for evaporative cooling system is Fabric defender 750 with Shelltite finish. From the experimental data and equations we have diffusion coefficient of 20.9 ± 3.71 x 10-6 m2/s for fabric with one layer with 17%-20% fluctuations from the theory, 27.8 ± 4.5 x 10-6 m2/s for fabric with two layers with 6%-14% fluctuations from the theory and 24.9 ± 4.1 x 10-6 m2/s for fabric with three layers with 13%-16% fluctuations from the theory. Since the thickness of the fabric increases so the mass transport rate decreases so the mass transport resistance should be increases. The intrinsic mass resistances of Fabri-1L, Fabri-2L and Fabri-3L are respectively 104 ± 10.2 s/m, 154 ± 23 s/m and 206 ± 26 s/m from the experiment.

Ground source cooling is commonly used for cooling of electronics in protected sites. Sometimes the boreholes are combined with free cooling from the air using a dry cooler to reduce the amount and length of the boreholes, which is the biggest part of the costs. The dry cooler can have two different running modes. In unloading mode the dry cooler is started at a certain temperature and the fans are slowed down at low temperatures so that the cooling power never exceeds the cooling demand. The extracted cooling is used to unload the boreholes. In recharging mode the dry cooler is started at a certain temperature and is operating at full capacity below this temperature. The excess cooling that is extracted in this mode is used to recharge the boreholes. The numerical simulation tool COMSOL Multiphysics was used to evaluate the borehole performance. The software can simulate tilted boreholes with good accuracy and makes it possible to adjust the geometry in any desired way. In this thesis, the performance of a 100 kW ground source cooling system is evaluated for a number of cases both with and without dry coolers in different running modes and sizes. The best solution in respect to life cycle cost, technical feasibility and environmental impact is chosen to be an unloading case with a dry cooler with 100 kW capacity at 8 °C. Using only boreholes gives less carbon dioxide emissions but much higher costs.

Transpiration cooling as potential replacement of multi-hole effusion cooling for gas turbine engines combustion liner application is investigated by comparing their cooling film effectiveness based on the mass transfer analogy (CFEM). Pressure sensitive paint was used to measure CFEM over PM surfaces which was found to be on average 40% higher than multi-hole effusion cooling. High porosity PM with low resistance to flow movement were found to offer uneven distribution of exiting coolant, with large amounts leaving the trailing edge, leading to lopsided CFEM. Design of anisotropic PM based on PM properties (porosity, permeability, and inertia coefficient) were investigated using numerical models to obtain more uniform CFEM. Heat transfer analysis of different PM showed that anisotropic samples offered better thermal protection over isotropic PM for the same porosity. Comparison between cooling film effectiveness obtained from temperatures CFET against CFEM revealed large differences in the predicted protection. This is attributed to the assumptions made to apply CFEM, nonetheless, CFEM remains a good proxy to study and improve transpiration cooling. A method for creating a CAD model of designed PM is proposed based on critical characteristics of transpiration cooling for future use in 3D printing manufacturing.

Building energy simulation has become a useful tool for predicting cooling, heating and electrical loads for facilities. Simulation models have been validated throughout the years by comparing simulation results to actual measured values. The simulations have become more accurate as approaches were changed to be more comprehensive in their ability to model building features. These simulation models tend to require considerable experience in determining input parameters and large amounts of time to construct the models. As a result of the large number of man-hours required, simplified models have been sought and used. Simplified models are particularly useful for conducting preliminary assessments of energy conservation measures. These simplified models often use linear relationships in order to estimate conditions such as infiltration, energy usage, and temperature gradients. Studies have been performed in order to validate popular models such as ASHRAE's Bin or Modified Bin methods. A useful measure would be to determine the accuracy of a simplified model to establish error bounds. Having a simplified model and establishing its error bounds, technical estimations from such models could be used in selected applications with more confidence. The error bound relative to DOE-2 predictions, for a proposed simplified model denoted IEC, for estimating a commercial building's cooling load are presented along with two actual-building test cases for validation purposes. The sensitivity of the error to various building parameters such as minimum make-up air, cooling capacity oversize, and internal equipment load was investigated. The error bound was determined to be within ±15 per cent for both cases and almost all variations. / Master of Science

Though the least squares technique has many advantages, its possible limitations as applied in the atmospheric sciences have not yet been fully explored in the literature. The assumption that the atmosphere responds either in phase or out of phase to the solar input is ubiquitous. However, our analysis found this assumption to be incorrect. If not properly addressed, the possible consequences are bias in the linear trend coefficient and attenuation of the solar response coefficient. Using USU Rayleigh lidar temperature data, we found a significant phase offset to the solar input in the temperatures that varies ±5 years depending on altitude. In addition to introducing a phase offset into the linear regression model, we argue that separating what we identify as the solar-noise is to be preferred because (1) the solar-noise can contain important physical information, (2) its omission could lead to spurious conclusions about the significance of the solar-proxy coefficient, and (3) its omission could also bias the solar proxy coefficient. We also argue that the Mt. Pinatubo eruption caused a positive temperature perturbation in our early mesopause temperatures, exerting leverage on the linear trend coefficient. In the upper mesosphere, we found a linear cooling trend of greater than -1.5 K/year, which is possibly exaggerated because of leverage from the earlier temperatures and/or collinearity. In the middle mesosphere we found a cooling trend of -1 K/year to near zero. We use the autocorrelation coefficient of the model residuals as a physical parameter. The autocorrelation can provide information about how strongly current temperatures are affected by prior temperatures or how quickly a physical process is occurring. The amplitudes and phases of the annual oscillation in our data compare favorably with those from the OHP and CEL French lidars, as well has the HALOE satellite instrument measurements. The semiannual climatology from the USU temperatures is similar to that from the HALOE temperatures. We also found that our semiannual and annual amplitudes and phases compare favorably with those from the HALOE, OHP, and CPC data.

Let X be a space and let S ⊂ X with a measure of set size |S| and boundary size |∂S|. Fix a set C ⊂ X called the constraining set. The constrained isoperimetric problem asks when we can find a subset S of C that maximizes the Følner ratio FR(S) = |S|/|∂S|. We consider different measures for subsets of R^2,R^3,Z^2,Z^3 and describe the properties that must be satisfied for sets S that maximize the Folner ratio. We give explicit examples.