Difusão de massa em corpos esféricos: soluções analíticas e numéricas, modelagens e aplicação na secagem de uvas sem sementes.

Abstract

In drying process for the conservation of agricultural products, it is indispensable to know the characteristics and properties of the materials that are used in order to develop the control and to dimension the place that will be used for storage. In this work it will be studied the liquid diffusion and some empirical models, and it will be made comparisons between the models, choosing the best one to describe drying of seedless grapes with the goal to produce raisins. In the drying study it was employed the liquid diffusion to describe the kinetics process of drying in spherical coordinates. In this work were studied models that will be analyzed considering boundary condition of the first and the third kind, constant and variable volume V, constant and variable effective mass diffusivity D, and constant convective mass transfer coefficient, h. The solutions of the diffusion equation (analytic and numerical) were used to determinate D and h using datasets from the literature. It was verified that the best model to describe drying of seedless grape must consider: 1) shrinkage; 2) boundary condition of the third kind; 3) variable effective mass diffusivity. After the analysis of the simulated data it was found that the best model for the diffusivity is a function of the type hyperbolic cosine. For this case, the errors may be considered with a random distribution.