Orientador: Milton Mori / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Química / Made available in DSpace on 2018-08-19T13:17:08Z (GMT). No. of bitstreams: 1 SilvaJunior_JoaoLameuda_M.pdf: 5288658 bytes, checksum: 05a82477d396e479ec1f137cc2682920 (MD5) Previous issue date: 2011 / Resumo: Esta pesquisa tem como objetivo avaliar as principais forças interfaciais que atuam no escoamento gás-líquido em uma coluna de bolhas retangular, de dimensões 150cm x 26;4cm x 3;1cm (altura (H) x largura (W) x profundidade (D)), com aeração centralizada, empregando a Fluidodinâmica Computacional (CFD). O caso proposto é baseado em um estudo experimental de um sistema ar-água operando em regime homogêneo, com altura inicial de líquido (Hl) igual a 79;2cm, correspondente a razão de aspecto (Hl /W) de 3. Empregou-se para a fase dispersa, um diâmetro de bolhas de 4;95mm e uma velocidade superficial de 2;9cm/s. Para validação do modelo, comparações com dados experimentais obtidos da literatura foram realizados em seções transversais em quatro níveis axiais (Y/Hl = 0;1; 0;2; 0;4; 0;75). Para o fechamento do modelo matemático foram analisados quatro modelos de turbulência na descrição da fase contínua (k-'épsilon', RNG k-'épsilon', LRR-RSM, SSG-RSM), bem como diferentes correlações para a verificação da influência das forças interfaciais envolvidas neste tipo de escoamento (arraste, sustentação, dispersão turbulenta e massa virtual). As forças de sustentação e dispersão turbulenta em adição à de arraste mostraram influências significativas nos padrões fluidodinâmicos, enquanto que a força de massa virtual pôde ser negligenciada para o caso estudado. O modelo completo final testado, predisse satisfatoriamente o escoamento em regiões onde este se encontra plenamente desenvolvido, concordando com o padrão experimental / Abstract: This study aims to evaluate the main forces which act in gas-liquid flow in a rectangular bubble column of dimensions 150cm x 26;4cm x 3;1cm (height (H) x width (W) x depth (D)), with centralized aeration, using CFD technique. The proposed case is based in a experimental study of an air-water system operating in homogeneous bubbly flow, with initial liquid height (Hl) of 79;2cm, corresponding to aspect ratio (Hl /W) of 3. For dispersed phase it was employed a bubble diameter of 4;95mm and a superficial velocity of 2;9cm/s. To validate the model, comparisons with experimental data provided from literature were carried out in transversal sections at four axial levels (Y/Hl = 0;1; 0;2; 0;4; 0;75). To closure the mathematical model, four distinct turbulence models were analyzed to describe the continuous phase (k--'épsilon', RNG k--'épsilon', LRR-RSM, SSG-RSM), as well different correlations to verify the influence of the interfacial forces involved in this type of flow (drag, lift, turbulent dispersion and virtual mass). The consideration of lift and turbulent dispersion in addition to drag force showed meaningful influences in fluid dynamics pattern, while virtual mass force can be neglected. The final complete model tested predicted properly the flow in fully developed regions, according to the experimental pattern / Mestrado / Processos em Tecnologia Química / Mestre em Engenharia Química

Orientadores: Milton Mori, Jhon Jairo Ramirez Behainne / Tese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia Química / Made available in DSpace on 2018-08-21T08:54:52Z (GMT). No. of bitstreams: 1 Hodapp_MaximilianJoachim_D.pdf: 4872915 bytes, checksum: 9619785faa8fc5ab19790d59903b0a7e (MD5) Previous issue date: 2012 / Resumo: A queima de carvão mineral em Leito Fluidizado Circulante (CFBC) tem interessado pesquisadores por várias décadas, tendo sido propostos inúmeros modelos matemáticos que visam descrever os complexos fenômenos de transferência de massa, energia e quantidade de movimento deste sistema gás-sólido. A fase sólida é uma mistura de materiais inertes, como a areia e a cinza de carvão, um agente desulfurizante, além do próprio combustível. A técnica de Fluidodinâmica Computacional tem sido aplicada com sucesso para simular não somente escoamentos multifásicos mas também problemas que envolvem reações químicas e troca de calor. Apesar disto, a caracterização individual dos diversos materiais da fase sólida não é muito estudada. Deste modo, neste trabalho foi pesquisada a representação numérica do escoamento no interior de um leito fluidizado por CFD. Numa primeira etapa estudou-se a fluidodinâmica gás-sólido a quente e numa segunda a implementação de uma abordagem trifásica para representar o processo de queima de carvão mineral. Assim, a fase gás e o material inerte foram considerados fluídos, conforme a abordagem Euleriana, enquanto o material reativo foi representado pela descrição Lagrangeana. A combustão ocorre principalmente num leito fluidizado de 4 m de altura e 0,1 m de diâmetro, operado no regime de baixa densidade de sólidos e rápida fluidização. As reações do sistema são aquelas que ocorrem na fase gasosa devido à liberação de voláteis do carvão, bem como a reação heterogênea do carbono. Os resultados das simulações CFD mostraram-se de acordo com os dados experimentais disponíveis para temperatura e composição dos gases de saída. A escolha de modelos de reação heterogênea e do inventário de sólidos do sistema se mostrou de grande importância à simulação do processo. Concluí-se que a abordagem trifásica apresentada mostra-se viável para sistemas nos quais a massa de material reativo sólido no sistema representa apenas uma fração da massa total dos sólidos presentes / Abstract: Coal combustion in Circulating Fluidized Bed Combustors (CFBC) has received great attention from researchers who have developed several approaches in order to model the complex phenomena of mass, energy and momentum exchange in this gas-solid system. The solid phase is usually a mixture of inert material, sand and ash, a desulfurization material such as limestone and the fuel itself. Computational Fluid Dynamics has been successfully applied to simulate not only the fluid dynamics of multiphase flow in components of CFBC's, but also to study the associated heat and mass transfer phenomena. However, the inclusion of more than one solid phase is not usually the · subject of research. Ideally each particle could be tracked in a Lagrangian formulation, which, for denser flows, could include inter-particle interactions. However even for small-scale plants the total number of particles by far exceeds currently available computing resources. In this work, a three-phase approach was applied to model fast bed CFBC riser, in which the gas phase and the inert particle phase are described in an Euler-trame while the reacting coal particles are tracked individually in a Lagrangian approach. A small pilot-plant unit feed with ash-rich Brazilian coal has been chosen as a study case. The combustion took place in a riser of 4m height and 0,1 m internal diameter, operating in the low-density regime. The chemical reactions in the system were those of the gas-phase homogeneous oxidation of the devolatilized components and the heterogeneous char combustion. The simulation results were in good agreement with experimental measurements for temperature and flue gas composition, hence the three-phase modeling showed to be a viable alternative to a more complete simulation of the CFBCs coal combustion process / Doutorado / Processos em Tecnologia Química / Doutor em Engenharia Química

Magister Scientiae - MSc / Nuclear reactors release small amounts of radioactivity during their normal operations. The most common method of calculating the dose to the public that results from such releases uses Gaussian Plume models. We are investigating these methods using CAP88-PC, a computer code developed for the Environmental Protection Agency (EPA) in the USA that calculates the concentration of radionuclides released from a stack using Pasquill stability classification. A buoyant or momentum driven part is also included. The uptake of the released radionuclide by plants, animals and humans, directly and indirectly, is then calculated to obtain the doses to the public. This method is well established but is known to suffer from many approximations and does not give answers that are accurate to be better than 50% in many cases. More accurate, though much more computer-intensive methods have been developed to calculate the movement of gases using fluid dynamic models. Such a model, using the code FLUENT can model complex terrains and will also be investigated in this work. This work is a preliminary study to compare the results of the traditional Gaussian plume model and a fluid dynamic model for a simplified case. The results indicate that Computational Fluid Dynamics calculations give qualitatively similar results with the possibility of including much more effects than the simple Gaussian plume model. / South Africa

Orientador: Sávio Souza Venâncio Vianna / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Química / Made available in DSpace on 2018-08-24T13:25:34Z (GMT). No. of bitstreams: 1 Ferreira_TatieleDalfior_M.pdf: 4562241 bytes, checksum: 69c742236e806f040cfc237f2ba91cf4 (MD5) Previous issue date: 2014 / Resumo: Este trabalho tem como objetivo desenvolver um modelo matemático capaz de prever o tamanho de nuvem de gás inflamável formada em uma típica plataforma de petróleo considerando condições reais de ventilação e de operação de uma planta de processo. Para tanto, foi realizado um estudo de dispersão de gás inflamável (gás natural) na plataforma em questão utilizando Fluidodinâmica Computacional (CFD). Os resultados deste estudo de dispersão serviram como base para a construção do modelo matemático utilizando Metodologia de Superfície de Resposta. Tal modelo permite o cálculo do tamanho de nuvem de gás inflamável no ambiente estudado usando duas variáveis principais: a taxa não-dimensional de vazamento (que contabiliza a relação entre a taxa de vazamento de gás e a taxa de ventilação na plataforma) e a direção adimensional de vazamento (que computa a relação entre as direções de vazamento de gás e do vento). O modelo desenvolvido mostrou-se eficaz, pois foi capaz de prever com considerável grau de confiabilidade os tamanhos de nuvem de gás inflamável quando comparados aos valores fornecidos por simulações com CFD / Abstract: This work proposes the development of a mathematical correlation for prediction of flammable gas cloud size in a typical offshore module. Real conditions regarding the ventilation and process plant operation were considered. A dispersion study of natural gas release in the module was conducted using Computational Fluid Dynamics (CFD) and the state of art as far as the gas dispersion modelling is concerned. A mathematical model was built based on the numerical results and Response Surface Methodology (RSM). The approach comprises into a single mathematical model the most relevant independent variables. The response surface curves calculate the flammable gas cloud volume as a function of the non-dimensional leak rate (that concerns the ventilation and the gas release rate) and the non-dimensional leak direction (which comprises the wind direction and the leak direction). The developed model had proved to be effective. It was able to predict flammable gas volume and good agreement with CFD results was observed / Mestrado / Sistemas de Processos Quimicos e Informatica / Mestra em Engenharia Química

Orientador: Sávio Souza Venâncio Vianna / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Química / Made available in DSpace on 2018-08-26T16:12:11Z (GMT). No. of bitstreams: 1 FerreiraJunior_ElmodeSena_M.pdf: 18188081 bytes, checksum: 2b445e8828a2a2b90c9a27c3379a7d74 (MD5) Previous issue date: 2015 / Resumo: A simulação numérica é de grande importância em diversas áreas da engenharia, tais como otimização e manutenção de processo químico, bem como na indústria do petróleo e segurança do processo. O Fire Dynamics Simulator (FDS) é um código de Fluidodinâmica Computacional com base na simulação das grandes escalas. Este foi desenvolvido pelo Instituto Nacional de Padrões e Tecnologia (NIST). O código FDS foi originalmente projetado para modelar baixo fluxo de velocidade comumente encontrados em cenários de incêndio. Assim, o FDS não é adequado para simulação de casos onde o número de Mach é elevado. Para superar esta limitação, este trabalho propõe um novo modelo dedicado às características próximas da saída do jato a fim de permitir o FDS simular cenários de jatos e dispersão de gás. A abordagem também reduz significativamente o tempo da simulação computacional. A ferramenta proposta é uma alternativa livre e confiável para a modelagem de dispersão de gás. Os resultados são amplamente discutidas e um estudo de caso de uma plataforma é apresentado. A comparação com os resultados experimentais, bem como um pacote CFD comercial mostram boa concordância / Abstract: The numerical simulation is of great importance in various areas of engineering such as optimization and maintenance of chemical process, petroleum industry and process safety. The Fire Dynamics Simulator (FDS) is a Computational Fluid Dynamics (CFD) code based on Large Eddy Simulation (LES) modeling and developed by National Institute of Standards and Technology (NIST). FDS code was originally designed to model low speed flow commonly found in fire scenarios. Hence, FDS is not suitable for modeling high Mach number cases. To overcome this limitation this work proposes a novel model dedicated to the near field jet characteristics in order to enable FDS to simulate jet scenarios and gas dispersion. The approach also reduces the computational time significantly as far as turbulent jet flows are concerned. The proposed tool is a free and reliable alternative for gas dispersion modeling. Results are extensively discussed and case study for a typical offshore site is presented. Comparison with experimental results as well as commercial CFD package show good agreement / Mestrado / Sistemas de Processos Quimicos e Informatica / Mestre em Engenharia Química

The master´s thesis deals with the numerical modeling of flow in the emergency spillways of small dams. It is solved the flow rate capacity of a weir and of spillway called „duckbill-type“. Sharp crested weirs and long crested weirs are modeled using numerical simulations in ANSYS. Hydraulically complex spillway called „duckbill-type“ was modeled in the Flow-3D. The results of the discharge coefficients are compared with data in the hydraulic literature.

Solar energy is one of a very few low-carbon energy technologies with the enormous potential to grow to a large scale. Currently, solar power is generated via the photovoltaic (PV) and concentrating solar power (CSP) technologies. The ability of CSPs to scale up renewable energy at the utility level, as well as to store energy for electrical power generation even under circumstances when the sun is not available (after sunset or on a cloudy day), makes this technology an attractive option for sustainable clean energy. The levelised electricity cost (LEC) of CSP with thermal storage was about 0.16-0.196 Euro/kWh in 2013 (Kost et al., 2013). However, lowering LEC and harvesting more solar energy from CSPs in future motivate researchers to work harder towards the optimisation of such plants. The situation tempts people and governments to invest more in this ultimate clean source of energy while shifting the energy consumption statistics of their societies from fossil fuels to solar energy. Usually, researchers just concentrate on the optimisation of technical aspects of CSP plants (thermal and/or optical optimisation). However, the technical optimisation of a plant while disregarding economic goals cannot produce a fruitful design and in some cases may lead to an increase in the expenses of the plant, which could result in an increase in the generated electrical power price. The study focused on a comprehensive optimisation of one of the main CSP technology types, the linear Fresnel collector (LFC). In the study, the entire LFC solar domain was considered in an optimisation process to maximise the harvested solar heat flux throughout an imaginary summer day (optical goal), and to minimise cavity receiver heat losses (thermal goal) as well as minimising the manufacturing cost of the plant (economic goal). To illustrate the optimisation process, an LFC was considered with 12 design parameters influencing three objectives, and a unique combination of the parameters was found, which optimised the performance. In this regard, different engineering tools and approaches were introduced in the study, e.g., for the calculation of thermal goals, Computational Fluid Dynamics (CFD) and view area approaches were suggested, and for tackling optical goals, CFD and Monte-Carlo based ray-tracing approaches were introduced. The applicability of the introduced methods for the optimisation process was discussed through case study simulations. The study showed that for the intensive optimisation process of an LFC plant, using the Monte Carlo-based ray-tracing as high fidelity approach for the optical optimisation objective, and view area as a low fidelity approach for the thermal optimisation objective, made more sense due to the saving in computational cost without sacrificing accuracy, in comparison with other combinations of the suggested approaches. The study approaches can be developed for the optimisation of other CSP technologies after some modification and manipulation. The techniques provide alternative options for future researchers to choose the best approach in tackling the optimisation of a CSP plant regarding the nature of optimisation, computational cost and accuracy of the process. / Thesis (PhD)--University of Pretoria, 2017. / Mechanical and Aeronautical Engineering / PhD / Unrestricted

Concern over the altering climate due to the release of anthropogenic greenhouse gases has caused a major shift in the developments of ways to minimise human impact on the climate. Solar energy is seen as one of the most promising sources to transform the energy market for low-carbon energy generation. Currently, solar power is generated via photovoltaic (PV) and concentrating solar power (CSP) technologies. The advantage of CSPs to scale up renewable energy to utility level, as well as to store thermal energy for electrical power generation when the sun is not available (after sunset or during cloudy periods) makes this technology an attractive option for sustainable clean energy. CSP development, however, is still in its infancy, and for it to be a competitive form of energy-generation technology, techno-economic developments in this field need to improve the efficiency and decrease the costs of this technology. A policy report by the European Academies’ Science Advisory Council (EASAC) (2011) indicated that central receiver (solar tower) CSP systems show the greatest margin for technological improvements (40% to 65% is estimated), and that an improvement in receiver technology could make the greatest contribution to increase efficiency. This study therefore focused on analysing the optical and thermal performance of a new proposed solar cavity molten salt receiver design for a central receiver CSP system using a numerical approach. In this study, the receiver’s performance was analysed by first selecting an existing heliostat field, Planta Solar 10 (PS-10). For the numerical analysis to reflect conditions that are as realistic as possible, numerical models for different aspects were selected and validated. For modelling the sun, the solar tracking numerical model proposed by Iqbal (1983) was selected and implemented after literature and comparison showed adequate results. The direct normal irradiation (DNI) was modelled by applying a clear sky model, with the parameterisation model C proposed by Iqbal (1983) as the chosen model. The variables in this model that were subject to temperature, and humidity values were more accurately presented by adding numerical approximations of the region’s actual weather data. The DNI model reflected realistic fluctuations. For the thermal modelling, a validation study was conducted on impingement flow heat transfer to select an appropriate Reynolds-averaged Navier-Stokes (RANS) model that would provide accurate results when conducting the thermal performance test on the receiver. The study concluded that the transitional Shear Stress Transport (SST) turbulence model performed the best. A new method was also developed and validated that allows one to not only simulate complex geometries within the Monte Carlo ray tracing environment SolTrace, but also to apply the results obtained by simulating this model as a heat source within the computational fluid dynamics (CFD) environment ANSYS Fluent. This allows SolTrace modelling to be more accurate, since models do not need to be approximated to simple geometries. It also provides an alternative for solar modelling in ANSYS Fluent. The optical analysis was conducted by first performing an analysis on the receiver aperture and studying its sensitivity on the captured flux. This was followed by analysing the optics of the proposed receiver, the flux distributions on a simplified absorber surface area, and how these distributions are altered by changing some parameters. An in-depth analysis was finally done on the absorber area by applying the aforementioned model to simulate complex geometries within SolTrace, with the results illustrating the difference of the detailed geometry on optical modelling. An alternative receiver design with improved optical features was proposed, with an initial study providing promising results. The thermal analysis was done within the CFD environment, with only a section of the absorber surface area considered, and by applying the solar flux simulated during the optical analysis as heat source within the geometry model. This allowed the model to simulate the effects of re-radiation at the surface of the absorber while simulating the heat transfer at the fluid molten salt side simultaneously. The results showed that, for the current design and requirements, the absorber surface temperature reaches impractical temperatures. Altering the design or being more lenient on the requirements has, however, shown dramatic improvements in terms of thermal performance. Sensitivity studies for both the optical and thermal analyses have shown that changes in design can dramatically improve the performance of the design, making it a possible feasible receiver design for central receiver systems. / Dissertation (MEng)--University of Pretoria, 2019. / National Research Foundation (NRF) / Mechanical and Aeronautical Engineering / MEng / Unrestricted

The DigIndy tunnel is an extension of the Indianapolis combined sewer system that stores the combined sewer overflow during heavy rain conditions. The tunnel system has several openings in and around the city of Indianapolis. Gasses emitted from the tunnel may create health concerns and affect the quality of life for nearby residents. Understanding the air circulation patterns provides valuable insight into where gases are likely to emerge from the tunnel and what steps may be taken to mitigate gas emissions in undesirable locations. The objective of the present work is to develop a computational fluid dynamics (CFD) model capable of predicting the air circulation patterns in the DigIndy tunnel under dry weather conditions. In order to inform and validate the CFD model, an experimental campaign was designed and executed to measure weather data and air flow rates within the DigIndy tunnel. Obtaining accurate results requires careful consideration of key physical phenomena to include in the model, geometric simplification strategies, mesh generation strategies, and numerical modeling strategies. Results showed that the seasonal effect, manifest by thermally-driven flow, plays a significant role in the air circulation patterns within the tunnel. Furthermore, results show that tunnel alignment affects the natural air circulation within the tunnel. Large diameter shafts, as the working and retrieval shafts, lead to significant circulation rates in the new tunnel alignments.

<p dir="ltr">This thesis examined the effect of variations in the geometry of the juncture of a cylinder at a flat plate. The effect on the pressure and skin friction on the face and surroundings were examined. When compared to the experimental data obtained under similar conditions, the computational cases had a slightly higher pressure, with a qualitatively similar profile. Four cases were considered: a simple baseline configuration, a pedestal, a gap, and a fairing. The results of the pedestal case displayed this behavior to an extreme, exaggerating all the jumps and dips in the experiment. The RMS pressure was examined to investigate the shock foot locations and again the experiment and computation matched very closely. When looking at the flow visualizations and spectra, the gap case showed a larger concentration of skin friction magnitude at the base as well as the highest intensity of the low frequencies at separation and reattachment, as well as an observed higher frequency activity like Liu observed in his computations. For the new fairing case that was introduced, very similar properties to the pedestal case were observed when looking at the pressure, skin friction, and even spectra, but the flow visualization in the wake showed that it was much closer in structure to the baseline case. The small differences between the computational and experimental data could be attributed to the turbulence model used as well as the uncertainty in the pressure sensitive paint technique used in the experiments. In this thesis it was found that the gap case had higher fluctuations and skin friction, the new fairing case was very similar to the pedestal and baseline case, and the experimental data matched well for most of the computations.</p>