Aplicação da termodinâmica de processos irreversíveis à análise de secagem e determinação de propriedades térmicas de materiais porosos, por meio de funções de base radial

• Ano de defesa: 2012
• Autor(a) principal: Santos, Gisele Tessari
• Orientador(a): Martins, José Helvécio
• Banca de defesa: Ferreira, Wanyr Romero , Silva, Sávio Augusto Lopes da , Silva, Jadir Nogueira da
• Tipo de documento: Tese
• Tipo de acesso: Acesso aberto
• Idioma: por
• Instituição de defesa: Universidade Federal de Viçosa
• Programa de Pós-Graduação: Doutorado em Engenharia Agrícola
• Departamento: Construções rurais e ambiência; Energia na agricultura; Mecanização agrícola; Processamento de produ
• País: BR
• Palavras-chave em Português: Funções de base radial; Secagem
• Palavras-chave em Inglês: Radial basis functions; Drying
• Área do conhecimento CNPq: CNPQ::CIENCIAS AGRARIAS::ENGENHARIA AGRICOLA
• Link de acesso: http://locus.ufv.br/handle/123456789/713

This work consists of three sections. The last two sections are related to the drying process analysis of wheat kernel. The first section presented a new numerical technique for solving transient problems of dispersion of contaminants in unsaturated soils. The numerical scheme served as basis for solving the complex drying equation. Cereal grains are useful to mankind and naturally complex. They are anisotropic, thermosensitive, biologically degradable under adverse psychrometric variations. Proper drying can minimize insect attack, mold growth, quality decay and undesired effects of environmental conditions. The number of variables that define grain drying is long and include, among others, product thermophysical properties, shape, biological composition and thermal and moisture content behavior, degree of anisotropy, end use and cost. The second section of this work aimed at analyzing wheat kernel drying as a means to know about its behavior under several environmental conditions for an eventual fine control of drying conditions. In this direction, an irreversible thermodynamics model composed of a system of two nonlinear partial differential equations, with temperature and equilibrium moisture content as dependent variables was solved. The numerical solution method consisted of a modified form of cubic radial basis functions scheme. The model was solved in spherical and cylindrical coordinates, with convective boundary conditions. Solutions with Dirichlet boundary conditions and spherical coordinates were also investigated and compared with the other solutions. The results showed excellent accuracy of the proposed models, pointing out that the use of Dirichlet boundary conditions may lead to high surface thermal and hydro gradients. A brief analysis is presented on the effect of shape and anisotropy on the proposed spherical isotropic model. Full graphical results for four different drying conditions are presented and discussed in detail. The third part of this study consisted of analysis of a wheat kernel with prolate ellipsoidal and spherical shapes in order to better define the appropriate model to simulate the drying process and allow eventual dryer project with minimization of thermal and hydro stress damage. As in the second section of this work, was used a model grounded on thermodynamics of irreversible processes consisting of a system of two nonlinear partial differential equations. The numerical solution scheme consisted of a modified form of the cubic radial basis functions, used to solve the model in cylindrical coordinates, with convective boundary conditions. The obtained coefficients included the transport coefficients of liquid, vapor and mass convection. The results compared favorably with experimental data and simulated results from Fortes et al. (1981). We present a brief discussion on the effect of shape and anisotropy on drying modeling. Results are presented for the drying condition specified by the air dry bulb temperature of 47.0°C, relative humidity of 33.8%,wheat kernel initial moisture content of 0.211 (dry basis) and air velocity of 1.5 m/s. As previously stated, the first section of this work was the basis for the study of thin layer drying model by means of the approach proposed by Fortes and Okos (1981). The main motivation was the fact that there are benchmark numerical solutions available to the soil pollution problem analyzed. This part presents, then, the method of radial basis functions (RBF) with a change in the treatment of the integration process as a tool to solve equations of advection or dispersion of contaminants. Its accuracy is compared against benchmark solutions obtained from the one-dimensional version of the commercial software HYDRUS. The results show that the proposed RBF method is a suitable option to solve problems dominated by advection and solute transport in soils. The solution obtained by means of HYDRUS introduces numerical dispersion into the results of the solute problem, while the modified RBF scheme does not lead to dispersion, scattering or false diffusion. The method has, therefore, proved itself to be an option for obtaining accurate solutions.