Estudo dos parâmetros de processo e modelagem numérica da secagem do resíduo sólido da produção do extrato hidrossolúvel de soja (Okara)

AUTOR(ES)
DATA DE PUBLICAÇÃO

2008

RESUMO

Abstract: The present work analyzes experimental and numerically the conjugated mass and heat transfer during the drying process of the residue obtained in the soy hidrosoluble extract production (okara). The drying process proposed in this work consists in submitting the extrusated okara in the shape of pellets to two process levels: at the first one the product is dehydrated in a pneumatic tube until the loss of the superficial adesivity and at the second one the pellets are dried in a rotational drum with lower temperatures until they achieve a desirable humidity content, that is, sufficient to avoid microbiological and/or enzymatic deterioration during storage. The process parameters, time, temperature and drum rotation, are correlated to the final product darkening level. The temperatures tested for the first process level are 170C, 150C and 130C (the highest temperatures that could be obtained experimentally in order to obtain high drying rates), the temperatures for the second level are 70C, 60C and 50C (temperatures that did not cause high darkening rates) and the drum rotations tested are 27 rpm and 47 rpm (rotations that could be used experimentally without causing damages to the drier adapted at laboratory). In order to achieve the goals of this work several drying processes were accomplished at different conditions of the process parameters quoted. For each process the humidity and temperature profiles at the pellets were measured experimentally and the product darkening level was evaluated visually. The best drying combination, in terms of process time and darkening level, is the one that uses 150C at the first level and 70C at the second one. The product submitted to this combined process has a drying period of 27 minutes and presents a light color. For the numerical analysis the drying governing equations, the Fourier s Law to the heat transfer and the Fick s Law to the mass transfer, were discretizated by the Implicit Finite Difference Method. All the okara termophysical properties utilized at the simulation, density, density of the solid fraction, specific heat, thermal conductivity, thermal diffusivity, mass diffusivity, heat transfer coefficient, mass transfer coefficient, as well as the water vaporization latent heat and the water vapor specific heat, were obtained by literature equations which utilize data obtained at laboratory. In order to calculate these properties, the porosity was considered inside the okara pellets. The processes were simulated numerically using Matlab and the numerical results were compared to the experimental ones. The results showed a high efficiency of the proposed drying method, that is, it was possible to obtain okara pellets with the desired water activity, with light color and with good formation, and an adequate agreement between experimental and numerical results (R>0.94).

ASSUNTO(S)

okara engenharia mecânica - dissertações materiais - propriedades térmicas engenharia mecanica secagem mechanical engineering massa - transferência drying okara análise numérica calor - transmissão heat numerical analysis materials mass transfer

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