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Abstract(s)
As câmaras de mistura são diversamente utilizadas em toda a indústria com o objetivo de uniformizar diversos tipos de misturas, nomeadamente, líquidos com líquidos, de líquidos com
sólidos, entre outros. Neste trabalho é mostrada a predominância de fenómenos turbulentos
dentro destas e o seu impacto na mistura de diversas espécies presentes nas câmaras.
A dinâmica dos fluidos computacional (CFD) tem vindo a ser vastamente utilizada na predição
dos fenómenos turbulentos de forma a caracterizar as estruturas do escoamento dentro deste
tipo de câmaras. A literatura descreve que os modelos RANS, que não têm em consideração as
características transitórias, falham diversas vezes nesta tarefa e que os modelos de resolução
completa da turbulência são demasiados dispendiosos para a utilização na indústria.
Nesta dissertação é feita a investigação dos impacto dos fenómenos de turbulência na mistura
de gases, com o objetivo de modelar computacionalmente o funcionamento da câmara da experiência CLOUD no CERN. Para tal é inicialmente enquadrado o objetivo nas características e
no estado da arte da modelação deste tipo de câmaras.
Posteriormente, são descritas as formulações físico-matemáticas dos processos de transporte
que estão na base da modelação numérica da mistura turbulenta. Os estudos têm por base a
utilização do modelo multifásico “MIXTURE” do código comercial FLUENT com duas variantes
para o modelo de turbulência, em que será utilizado o modelo k - ? SST URANS e o SAS.
Os resultados obtidos são validados com dados da literatura, analisando a mistura de dois gases
numa junção em T. É utilizada uma geometria de forma a que se consiga ter pouca difusão
numérica e de facto ver a relação do modelo de turbulência com os fenómenos de mistura de
espécies.
Por fim, é aplicado o modelo multifásico para a mistura de Ar e de SO2 na câmara de mistura
da experiência CLOUD. As simulações foram feitas em articulação com ambos os modelos de
turbulência, SST e SAS, que demonstraram resultados significativamente diferentes. O modelo
de turbulência comporta-se sempre melhor do que o SST para os vários casos analisados.
Mixing chambers are used throughout the industry in order to homogenize various types of mixtures, namely liquids with liquids, liquids with solids, among others. In this work it is shown the predominance of turbulent phenomena within these and their impact on the mixture of several species present in the chambers. Computational Fluid Dynamics (CFD) has been widely used in the prediction of turbulent phenomena in order to characterize the flow structures within this type of chambers. The literature describes that RANS models, which do not take into account the transient characteristics, fail several times in this task and that complete turbulence resolution models are too expensive for use in industry. In this dissertation the investigation of the impact of the turbulence phenomena in the gas mixture is made, with the objective of computationally modeling the camera operation of the CLOUD experiment at CERN. To this end, it is initially framed the objective in the characteristics and state of the art of the modeling of this type of chambers. Subsequently, the physical-mathematical formulations of the transport processes that underlie the numerical modeling of the turbulent mixture are described. The studies are based on the multi-phase model “MIXTURE” of the FLUENT commercial code with two variants for the turbulence model, in which the model k - ? SST URANS and SAS will be used. The results obtained are validated with data from the literature, analyzing the mixture of two gases in a T junction. A geometry is used in order to have little numerical diffusion and in fact to see the relation of the turbulence model with the phenomena of mixture of species. Finally, the multiphase model for the mixture of Ar and SO2 in the mixing chamber of the CLOUD experiment is applied. The simulations were done in conjunction with both turbulence models, SST and SAS, which demonstrated significantly different results. The turbulence model always behaves better than the SST for the various cases analyzed.
Mixing chambers are used throughout the industry in order to homogenize various types of mixtures, namely liquids with liquids, liquids with solids, among others. In this work it is shown the predominance of turbulent phenomena within these and their impact on the mixture of several species present in the chambers. Computational Fluid Dynamics (CFD) has been widely used in the prediction of turbulent phenomena in order to characterize the flow structures within this type of chambers. The literature describes that RANS models, which do not take into account the transient characteristics, fail several times in this task and that complete turbulence resolution models are too expensive for use in industry. In this dissertation the investigation of the impact of the turbulence phenomena in the gas mixture is made, with the objective of computationally modeling the camera operation of the CLOUD experiment at CERN. To this end, it is initially framed the objective in the characteristics and state of the art of the modeling of this type of chambers. Subsequently, the physical-mathematical formulations of the transport processes that underlie the numerical modeling of the turbulent mixture are described. The studies are based on the multi-phase model “MIXTURE” of the FLUENT commercial code with two variants for the turbulence model, in which the model k - ? SST URANS and SAS will be used. The results obtained are validated with data from the literature, analyzing the mixture of two gases in a T junction. A geometry is used in order to have little numerical diffusion and in fact to see the relation of the turbulence model with the phenomena of mixture of species. Finally, the multiphase model for the mixture of Ar and SO2 in the mixing chamber of the CLOUD experiment is applied. The simulations were done in conjunction with both turbulence models, SST and SAS, which demonstrated significantly different results. The turbulence model always behaves better than the SST for the various cases analyzed.
Description
Keywords
Câmaras de Mistura Dinâmica de Fluidos Computacional (Cfd) Junção T Mistura Turbulenta