EE - Artigos Publicados em Periódicos
URI permanente para esta coleçãohttps://rihomolog.furg.br/handle/1/513
Navegar
12 resultados
Resultados da Pesquisa
- 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,
- 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.
- 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.
- ItemGeometric optimization based on the constructal design of perforated thin plates subject to buckling(2012) Rocha, Luiz Alberto Oliveira; Real, Mauro de Vasconcellos; Correia, Anderson Luis Garcia; Vaz, Joaquim; Santos, Elizaldo Domingues dos; Isoldi, Liércio AndréElastic buckling is an instability phenomenon that can occur if a slender and thin-walled plate is subjected to axial compressive load. It is well known that the presence of holes in structural plate elements is almost inevitable in inspection, maintenance, and service purposes, or to reduce the structural weight. In this paper constructal design was employed to optimize the geometry of thin perforated plates submitted to elastic buckling. Simply supported rectangular perforated plates were analyzed with three different shapes of centered holes: elliptical, rectangular, and diamond. The purpose was to obtain the optimal geometry that maximizes the critical buckling load. The ratio between the height and length of the plate was kept constant, while the ratio between the characteristic dimensions of the holes was optimized for several hole volume fractions (φ). A finite-element model was used to assess the plate buckling load, and the Lanczos method was applied to the solution of the corresponding eigenvalue problem. When φ ≤ 0.20 the optimum geometry is the diamond hole, reaching maximum buckling loads around 80.0,21.5, and 17.4% higher than a plate without perforation and plates with elliptical and rectangular holes, respectively. For intermediate and higher values of φ, the elliptical and rectangular holes, respectively, led to the best performance. The optimal shapes were obtained according to the constructal principle of minimization of distribution of imperfections, showing that the constructal design also can be employed to define the optimized geometries in the mechanics of material problems.
- ItemNumerical investigation about the improvement of the thermal potential of an Earth-Air Heat exchanger (EAHE) employing the Constructal Design method(2015) Rodrigues, Michel Kepes; Brum, Ruth da Silva; Vaz, Joaquim; Rocha, Luiz Alberto Oliveira; Santos, Elizaldo Domingues dos; Isoldi, Liércio AndréThe Earth-Air Heat Exchanger (EAHE) is a device used to improve the thermal condition of built environments, allowing the reduction of electrical energy consumption of traditional air conditioner systems. Fundamentally, its operational principle is based on fluid mechanics and heat transfer, areas in which Constructal Design has been widely used to seek for the optimal geometries, i.e., which leads to the best performances. In spite of this fact, the employment of Constructal Design for improvement of the EAHE thermal potential has not been performed into literature. Therefore, the main purpose of this work is to perform a numerical investigation on different geometrical configurations of an EAHE using the Constructal Design to obtain the highest thermal potential. Results indicated that, for the same area occupied by the ducts and fixed mass flow rate of air, the increase of the number of ducts (complexity of geometry) improved the EAHE thermal performance up to approximately 73% for cooling and 115% for heating.
- ItemConstructal design of convective cavities inserted into a cylindrical solid body for cooling(2015) Lorenzini, Giulio; Estrada, Emanuel da Silva Diaz; Santos, Elizaldo Domingues dos; Isoldi, Liércio André; Rocha, Luiz Alberto OliveiraThis work applies Constructal design to study numerically the geometry of cavities bathed by a fluid with constant heat transfer coefficient that are intruded into a cylindrical solid body. The objective is to minimize the maximum excess of temperature between the solid body and the ambient by morphing the cavity geometry. Internal heat generating is distributed uniformly into the solid body which has adiabatic conditions on the outer surfaces. The total volume and the volume of the cavities are fixed. The cavities are rectangular with variable aspect ratio. The optimized geometry and performance are reported as functions of the ratio between the volume of the cavities and the total volume, the number of cavities and the dimensionless parameter that accounts for the convective heat transfer, λ. The main results indicate that for fixed number of cavities, ϕc, and dimensionless parameter λ, there is an optimal number of cavities, No, that minimizes the maximum excess of temperature and this optimal number of cavities in general increases as ϕc and λ increases.
- ItemConstructal design of T-shaped assemblies of fins cooling a cylindrical solid body(2014) Lorenzini, Giulio; Biserni, Cesare; Corrêa, Roberta de Lima; Santos, Elizaldo Domingues dos; Isoldi, Liércio André; Rocha, Luiz Alberto OliveiraThis paper considers the numerical optimization of a T-shaped assembly of fins cooling a cylindrical solid body. The objective is to minimize the maximum excess of temperature between the solid cylindrical body and the ambient. Internal heat generation is distributed uniformly throughout the solid body. The assemblies of fins are bathed by a steady stream with constant ambient temperature and convective heat transfer. The outer surfaces of the cylindrical body are adiabatic. The total volume of the body and the total volume of the fins are fixed, but the lengths of the fins can vary. The initial simulations demonstrated that the optimal performance is achieved when the tributaries shape becomes slender and the stem thicker so that the system has more freedom to morph. However, when the number of assembly exceeds 2, the best configuration is the one that presents slender stems and shorter tributaries. The reason of this sudden change in behavior is that the tributaries length is limited by the presence of the neighbor assembly of fins: the system becomes “locked” and has no more freedom to morph. Finally, a digression on how the number of T-shaped fin assembly affects the configuration patterns concludes the paper.
- ItemConstructal design of a vortex tube for several inlet stagnation pressures(2012) Marques, Crístofer Hood; Isoldi, Liércio André; Santos, Elizaldo Domingues dos; Rocha, Luiz Alberto OliveiraThe present paper shows a numerical study concerned with the geometrical optimization of a vortex tube device by means of Constructal Design for several inlet stagnation pressures. In the present study, it is evaluated a vortex tube with two-dimensional axisymmetric computational domain with dry air as the working fluid. The compressible and turbulent flows are numerically solved with the commercial CFD package FLUENT, which is based on the Finite Volume Method. The turbulence is tackled with the k-ε model into the Reynolds Averaged Navier-Stokes (RANS) approach. The geometry has one global restriction, the total volume of the cylindrical tube, and four degrees of freedom: d3/D (the ratio between the diameter of the cold outlet and the diameter of the vortex tube), d1/D (the ratio between the diameter of the inlet nozzle and the diameter of the vortex tube), L2/L (the ratio between the length of the hot exit annulus and the length of the vortex tube) and D/L (the ratio between the diameter of the vortex tube and its length). The degree of freedom L2/L will be represented here by the cold mass fraction (yc). In the present work it is optimized the degrees of freedom yc and d3/D while the other degrees of freedom and the global restriction are kept fixed. The purpose here is to maximize the amount of energy extracted from the cold region (cooling effect) for several geometries, as well as, investigate the influence of the inlet stagnation pressure over the optimal geometries. Results showed an increase of the twice maximized cooling heat transfer rate of nearly 330 % from 300 kPa to 700 kPa. Moreover, the optimization showed a higher dependence of (d3/D)o for the lower range of inlet pressures, while the optimization is more dependent of yc,oo for higher inlet stagnation pressures.
- ItemTwo-dimensional geometric optimization of an oscillating water column converter in laboratory scale(2012) Gomes, Mateus das Neves; Nascimento, Cristina Dias do; Bonafini, Beatriz Leandro; Santos, Elizaldo Domingues dos; Isoldi, Liércio André; Rocha, Luiz Alberto OliveiraThe present paper presents a two-dimensional numerical study about the geometric optimization of an ocean Wave Energy Converter (WEC) into electrical energy that has as operational principal the Oscillating Water Column (OWC). To do so, the Constructal Design fundamentals were employed to vary the degree of freedom H1/L (ratio between height and length of the OWC chamber), while the other degree of freedom H2/l (ration between height and length of chimney) was kept constant. The OWC chamber area (φ1) and the total OWC area (φ2) are also kept fixed, being the problem constraints. In this study was adopted a regular wave with laboratory scale dimensions. The main goal was to optimize the device’s geometry aiming to maximize the absorbed power when it is subjected to a defined wave climate. For the numerical solution it was used the Computational Fluid Dynamic (CFD) commercial code FLUENT®, which is based on the Finite Volume Method (FVM). The multiphasic Volume of Fluid (VOF) model was applied to treat the water-air interaction. The computational domain was represented by an OWC device coupled into a wave tank. Thereby, it was possible to analyze the WEC subjected to regular wave incidence. An optimal geometry was obtained for (H1/L)o=0.84, being this one approximately ten times more efficient then the worst case (H1/L = 0.14), showing the applicability of Constructal Design in this kind of engineering problem.
- ItemConstructal design applied to the elastic buckling of thin plates with holes(2013) Rocha, Luiz Alberto Oliveira; Isoldi, Liércio André; Real, Mauro de Vasconcellos; Santos, Elizaldo Domingues dos; Correia, Anderson Luis Garcia; Lorenzini, Giulio; Biserni, CesareElastic buckling is an instability phenomenon that can occur if a slender and thin plate is subjected to axial compression. An important characteristic of the buckling is that the instability may occur at a stress level that is substantially lower than the material yield strength. Besides, the presence of holes in structural plate elements is common. However these perforations cause a redistribution in plate membrane stresses, significantly altering their stability. In this paper the Bejan’s Constructal Design was employed to optimize the geometry of simply supported, rectangular, thin perforated plates subjected to the elastic buckling. Three different centered hole shapes were considered: elliptical, rectangular and diamond. The objective function was to maximize the critical buckling load. The degree of freedom H/L (ratio between width and length of the plate) was kept constant, while H0/L0 (ratio between the characteristic dimensions of the holes) was optimized for several hole volume fractions (φ). A numerical model employing the Lanczos method and based on the finite element method was used. The results showed that, for lower values of φ the optimum geometry is the diamond hole. For intermediate and higher values of φ, the elliptical and rectangular hole, respectively, led to the best performance.