Douglas Junior Nicolin

Assessment of the initial moisture content on soybean drying kinetics and transport properties

ABSTRACT Several researchers have developed studies to obtain a mathematical model able to describe grain drying kinetics. However, most of these studies neglect the effect of grain initial moisture content on drying curves. In this study, we assessed the dependence of drying curves and mass transfer coefficients on this initial moisture, air temperature, and its velocity by measuring grain mass losses within time on a tray dryer. Mathematical models were adjusted and results indicated that initial grain moisture content has significant influence on drying curves and mass transfer coefficients.

Stefan Problem Approach Applied to the Diffusion Process in Grain Hydration

The Stefan problem approach was applied to the mathematical modeling of the diffusion process that occurs during hydration of soybean grains. This technique considers that the boundaries of the problem are unknown, and finding them is a task, which is also part of the problem. The problem has boundaries which move along time. The governing differential equations are numerically solved for the case of transient diffusion equation, and an analytical solution is obtained for the hydration fronts by considering the pseudo-steady-state hypothesis for the diffusion equation. The behavior of hydration fronts was analyzed, which are defined by the moving boundaries, and their velocities for both cases and the main differences were analyzed in terms of considering or not the transient term of the diffusion equation. The results show the main differences in the behavior of hydration fronts that arise when the transient term is taken into account or the pseudo-steady-state hypothesis is considered and compare the obtained behaviors with experimental data.

Numerical Solution of a Nonlinear Diffusion Model for Soybean Hydration with Moving Boundary

Abstract Variable diffusivity and volume of the grains are taken into account in the diffusion model that describes mass transfer in soybean hydration. The variable space grid method (VSGM) was used to consider the increase in grain size, and the diffusivity was considered an exponential function of the moisture content. An equation for the behavior of the grain radius as a function of time was obtained by global mass balance over the soybean grain and the differential equation considered that the increase in radius happens due to the influence of the convective and diffusive fluxes at the surface of the grains. The model was solved by an explicit numerical scheme which presented satisfactory results. The results showed the behavior of moisture profiles obtained as a function of time and radial position and also showed how the grain radius increased with time and changed the solution domain of the diffusion equation.

Parboiled Rice and Parboiling Process

Rice, being cultivated and consumed on all continents, has great social and economic importance. Among the forms of grain processing, parboiling stands out because of its numerous physical and nutritional benefits. However, there are few literature researches devoted to the survey of these data. Given the relevance of parboiling and parboiled rice to the world population, this work provides a critical and systematic review of the parboiling process, including thermodynamic properties, environmental and social impacts, as well as relevant information on parboiled rice, considering its consumption and health benefits. Additionally, a pioneering review is presented on new technologies applied to the process, and mathematical modeling as a tool for optimization and migration of nutrients (vitamins and minerals) and contaminants (mycotoxins and chemical agents). Covering such diverse information, including both positive and negative results, allows a global understanding of the nature of the process and the product. Therefore, this literature review aims to provide broad knowledge, for laypeople, entrepreneurs, and researchers alike.

DIFUSÃO DE UMIDADE EM GRÃOS DE SOJA COMO UM PROBLEMA DO TIPO STEFAN: MODELAGEM MATEMÁTICA E VALIDAÇÃO EXPERIMENTAL

RESUMO O processo de transporte de calor ou massa num meio pode ocasionar o aumentou ou diminuicao em seu tamanho. Para que este fenomeno seja considerado na modelagem matematica da difusao, considera-se que o sistema possui contornos moveis, que refletem a variacao no tamanho do sistema. Tais problemas sao tradicionalmente conhecidos como problemas de Stefan. Graos de soja sofrem, em media, um aumento de 30~40% em seu tamanho ao absorverem umidade. Para modelar matematicamente a difusao de umidade em graos de soja foi utilizada a Segunda Lei de Fick da Difusao, sendo que os graos foram considerados esfericos. O modelo foi resolvido numericamente apos ter sido modificado pelo Metodo da Malha Espacial Variavel (MMEV), que inseriu na equacao da difusao o aumento de tamanho que os graos sofrem ao absorverem umidade. Os valores de difusividade foram ajustados e apresentaram aumento em funcao da temperatura. Foram obtidos os perfis de umidade internos e tambem os perfis de umidade medios em funcao do tempo, que se ajustaram satisfatoriamente aos dados experimentais. O movimento do contorno do sistema (raio dos graos) foi comparado com dados experimentais, obtidos por analise de imagem. Houve desvios entre a previsao do raio em funcao do tempo pelo modelo e valores experimentais devidos, principalmente, ao aumento irregular do tegumento dos graos numa direcao preferencial em dado momento da absorcao de umidade. A abordagem deste trabalho pode ser usada em problemas de difusao de calor.