EE - Artigos Publicados em Periódicos
URI permanente para esta coleçãohttps://rihomolog.furg.br/handle/1/513
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36 resultados
Resultados da Pesquisa
- ItemNumerical study of the influence of geometric parameters on the avaliable power in a solar chimney(2015) Vieira, Rodrigo Spotorno; Garcia, Claudio; Acunha Junior, Ivoni Carlos; Souza, Jeferson Avila; Rocha, Luis Alberto Oliveira; Isoldi, Liércio André; Santos, Elizaldo Domingues dosIn the presented work, it is made a numerical study about the main physical principle of a solar chimney (SCPP – Solar Chimney Power Plant) and the influence of some geometric parameters on the available power in the SCPP. The main objectives are to test the applicability of the studied numerical model in future studies of SCPP geometric optimization and to test the action of the collector inlet height (H1) and the chimney outlet diameter (D2) on the available power of the device. For that it is considered an incompressible, turbulent, steady flow with mixed convective heat transfer in a two-dimensional and axisymmetric domain, similar to the one found in a solar chimney. The conservation equations of mass, momentum and energy are numerically solved using the finite volume method, more specifically with the FLUENT software. The classical turbulence modeling (RANS) was used for the turbulence approach with standard model k – ε. The other geometric parameters: collector radius (R) and the inlet and outlet of the turbine section, R1 and R2, are also constant. The verification results indicated a good agreement with those presented in the literature, even using a simplified domain. It was also observed that the H1 parameter is almost insensitive in the solar chimney performance, whereas the D2 variable presented great influence in the available power. The best performance was attained for an intermediate value of D2, D2 = 0.44 m. For this value, the available power was almost 72% and 19% higher from those obtained in the inferior and superior extremes of the studied D2 variable, D2 = 0.22 m and 0.88 m, respectively. It was also observed that there is a very good possibility of optimization of the chimney geometry in future studies.
- ItemNumerical analysis including pressure drop in oscillating water column device.(2015) Gomes, Mateus das Neves; Santos, Elizaldo Domingues dos; Isoldi, Liércio André; Rocha, Luiz Alberto OliveiraThe wave energy conversion into electricity has been increasingly studied in the last years. There are several proposed converters. Among them, the oscillatingwater column (OWC) device has been widespread evaluated in literature. In this context, the main goal of this work was to perform a comparison between two kinds of physical constraints in the chimney of the OWC device, aiming to represent numerically the pressure drop imposed by the turbine on the air flow inside the OWC. To do so, the conservation equations of mass,momentumand one equation for the transport of volumetric fraction were solved with the finite volume method (FVM). To tackle thewater-air interaction, the multiphase model volume of fluid (VOF)was used. Initially, an asymmetric constraint inserted in chimney duct was reproduced and investigated. Subsequently, a second strategywas proposed,where a symmetric physical constraint with an elliptical shapewas analyzed. Itwas thus possible to establish a strategy to reproduce the pressure drop in OWC devices caused by the presence of the turbine, as well as to generate its characteristic curve.
- Item3D numerical analysis about the shape influence of the hydro-pneumatic chamber in an oscillating water column (owc).(2015) Isoldi, Liércio André; Grimmler, Juliana do Amaral Martins; Letzow, Max; Souza, Jeferson Avila; Gomes, Mateus das Neves; Rocha, Luis Alberto Oliveira; Santos, Elizaldo Domingues dosThe oceans represent one of the major energy natural resources, which potentially can be used to supply the World energy demand. In the last decades some devices to convert the wave ocean energy into electrical energy have been studied. In this work the operating principle of an Oscillating Water Column (OWC) converter was analyzed with a transient 3D numerical methodology, using the Finite Volume Method (FVM) and the Volume of Fluid (VOF) model. The incident waves on the OWC hydropneumatic chamber cause an oscillation of the water column inside the chamber producing an alternate air flow through the chimney. The air drives a turbine that is coupled to an electric generator. The aim of this work was to investigate the shape influence of the hydro-pneumatic chamber geometry in the air flow. For this, six cases were studied in laboratory scale and the results showed that the variation of the OWC chamber shape can improve 12.4% the amount of mass air flow.
- ItemConstructal design of a tubular array subjected to forced convection.(2015) Pedrotti, Vagner Andrade; Souza, Jeferson Avila; Santos, Elizaldo Domingues dos; Isoldi, Liércio AndréIn this work a tubular array (four tubes) subjected to a transverse forced flow is analyzed in terms of thermal performance. Taking into account that there are two main assembles usually used in heat exchanger equipment (aligned and staggered), and that there exist an uncountable number of possible assembles for an array of tubes, present work proposes to use the Constructal Theory to build an optimized assemble. The distance between tubes (p), and the region where tubes can be positioned are the geometric constraint of the problem. Four values for p were considered: p = 1.25D (tube diameter), p = 1.5D, p = 2D, p is free (no restriction). Fluid flow is considered bi-dimensional, incompressible and laminar with ReD = 10 and Pr = 0.71. Mass, momentum and energy equations were solved by the Finite Volume Method (FVM) using FLUENT software. Geometry creation and mesh generation were performed with GMSH software while VISIT software was used for the post processing. Results have shown that imposing no restriction to tube positioning do not necessarily lead to best system thermal performance. In this particular study, setting p = 2D has resulted in best thermal performance. Keywords: tubular assemble, optimization,
- ItemNumerical study of forced convection lid-driven cavity flows using LES (Large Eddy Simulation)(2013) Santos, Elizaldo Domingues dos; Petry, Adriane Prisco; Rocha, Luiz Alberto Oliveira; França, Francis Henrique RamosThis study presents the LES (large eddy simulation) of forced convection in laminar and two dimensional turbulent flows when the flow reaches the steady state. The main purpose is the evaluation of a developed numerical methodology for the simulation of forced convection flows at various Reynolds numbers (100 ≤ ReH ≤ 10,000) and for a fixed Prandtl number (Pr = 1.0). The hexahedral eight-node FEM (finite element method) with an explicit Taylor-Galerkin scheme is used to obtain the numerical solutions of the conservation equations of mass, momentum and energy. The Smagorinsky model is employed for the sub-grid treatment. The time-averaged velocity and temperature profiles are compared with results of literature and a CFD (computational fluid dynamics) package based on finite volume method, leading to a highest deviation of nearly 6%. Moreover, characteristics of the forced convection flows are properly obtained, e.g., the effect of the Reynolds number over the multiplicity of scales.
- ItemComputational modeling of RTM and LRTM processes applied to complex geometries(2012) Porto, Joseane da Silva; Letzow, Max; Santos, Elizaldo Domingues dos; Amico, Sandro Campos; Souza, Jeferson Avila; Isoldi, Liércio AndréLight Resin Transfer Molding (LRTM) is a variation of the conventional manufacturing process known as Resin Transfer Molding (RTM). In general terms, these manufacturing processes consist of a closed mould with a preplaced fibrous preform through which a polymeric resin is injected, filling the mold completely, producing parts with complex geometries (in general) and good finish. Those processes differ, among other aspects, in the way that injection occurs. In the RTM process the resin is injected through discrete points whereas in LRTM it is injected into an empty channel (with no porous medium) which surrounds the entire mold perimeter. There are several numerical studies involving the RTM process but LRTM has not been explored enough by the scientific community. Based on that, this work proposes a numerical model developed in the FLUENT package to study the resin flow behavior in the LRTM process. Darcy’s law and Volume of Fluid method (VOF) are used to treat the interaction between air and resin during the flow in the porous medium, i.e. the mold filling problem. Moreover, two three-dimensional geometries were numerically simulated considering the RTM and LRTM processes. It was possible to note the huge differences about resin flow behavior and filling time between these processes to manufacture the same parts.
- ItemConstructal design of a x-shaped cavity cooled by convection(2014) Link, Fernanda Bichet; Rocha, Luiz Alberto Oliveira; Santos, Elizaldo Domingues dos; Isoldi, Liércio AndréThis paper applies Constructal design to study the geometry of a X-shaped cavity that penetrates into a solid conductive wall. The objective is minimizing the dimensionless maximal excess of temperature between the solid body and the cavity. There is uniform heat generation on the solid body. The cavity surfaces are cooled by convection heat transfer while the solid body is subjected to adiabatic conditions on its outer surfaces. The total volume and the cavity volume are fixed, but the lengths and thickness of the X-shaped cavity can vary. The emerged optimal configurations and performance are reported. The effect of the area fraction φ which denotes the ratio between the cavity area and the total area of the geometry, and the ratio between the length and thickness of the branch cavity, H1/L1, on the dimensionless maximal excess of temperature is numerically investigated. The results show that the dimensionless maximal excess of temperature θmax,min decreases approximately 60% when the cavity fraction increases from φ = 0.05 to 0.25. The results also show that the X-shaped cavity performs approximately 45% better when compared to a C-shaped cavity under the same thermal conditions. The optimal X-shaped cavity is also in accordance with the optimal distribution of imperfections principle.
- ItemA matlab code to fit periodic data(2015) Brum, Ruth da Silva; Ramalho, Jairo Valões de Alencar; Rocha, Luiz Alberto Oliveira; Isoldi, Liércio André; Santos, Elizaldo Domingues dosThis paper presents a computer method to find the best sine-based function, in the sense of least squares, to fit periodic data. Even though the least squares method is not a novelty, there is a void in the literature about its use to find trigonometric functions, particularly when it gives rise to nonlinear systems, as it is done in this article. The respective code, implemented in the Matlab programming language, is detailed and analyzed exploring experimental data from the air and soil temperatures measured along the year in earth air heat exchangers (EAHE) built in the facilities of a case study house in the Brazilian state of Rio Grande do Sul. The fitting curves have been employed by the authors in different works to define boundary conditions to study new computer models of EAHE.
- ItemOtimização geométrica de um arranjo triangular de cilindros submetido a escoamento laminar com convecção forçada(2015) Galarça, Marcelo Moraes; Cardoso, Felipe Rodrigues; Razera, Andre Luis; Acunha Junior, Ivoni Carlos; Isoldi, Liércio André; Porte, Anderson Favero; Rocha, Luiz Alberto Oliveira; Santos, Elizaldo Domingues dosO presente trabalho numérico estuda o arranjo triangular de cilindros submetidos a escoamentos transientes, bi-dimensionais, incompressíveis, laminares e com convecção forçada por meios do método Constructal Design. As simulações foram realizadas para escoamentos com números de Reynolds e Prandtl de ReD = 100 e Pr = 0.71. As equações de conservação de massa, quantidade de movimento e energia foram resolvidas com o uso do método de volumes finitos (FVM – do inglês: Finite Volume Method). A área ocupada pelos três cilindros é uma restrição geométrica do problema, enquanto as razões ST/D (passo transversal sobre o diâmetro) e SL/D (passo longitudinal sobre o diâmetro) são os graus de liberdade. Vale destacar que os diâmetros dos três cilindros são iguais em todos os casos. O principal objetivo aqui é avaliar qual razão ST/D minimiza o coeficiente de arrasto e maximiza a taxa de transferência de calor (número de Nusselt) entre os cilindros e o escoamento circundante, i.e., um problema multiobjetivo. Em todos os casos foi considerada uma razão SL/D = 3.5. Os resultados mostraram que o comportamento fluidodinâmico e térmico foi bastante influenciado pela razão ST/D. O coeficiente de arrasto (CD) mínimo e o máximo número de Nusselt (NuD) são obtidos para ST/D = 1.5 e 5.5, respectivamente. Contudo, os melhores arranjos considerando a função multiobjetivo (arrasto e transferência de calor) foram alcançados na região ST/D ~ 2.0, mais próximo do ótimo obtido para o problema fluidodinâmico, ao contrário do observado para um caso de par de cilindros abordado na literatura.
- ItemExperimental and numerical analysis of an earth-air heat exchanger(2011) Vaz, Joaquim; Sattler, Miguel Aloysio; Santos, Elizaldo Domingues dos; Isoldi, Liércio AndréThe need to develop new technologies that allow the use of sustainable alternative sources of energy is increasingly evident. Thus, this work presents an experimental and numerical study of earth–air heat exchangers, which are used to reduce consumption of conventional energy for heating and cooling of built environments through the use of thermal energy contained in the soil. The experiment was conducted in southern Brazil in the city of Viamão, and its results were used to validate the computational modeling of heat exchangers. In the present work, the variation of air temperature inside the ducts, to an annual cycle, was investigated. The numerical solution of the conservation equations of the problem is performed with a commercial code (FLUENT) which is based on the Finite Volume Method (FVM). Turbulence is tackled with the Reynolds Stress Model (RSM). The transient temperature fields predicted numerically was compared with the experimental ones, the highest difference found was lower than 15%. The results showed the validity and effectiveness of the employed computational model, enabling its use for future researches and projects developments about earth–air heat exchangers.