Nonisotropic Mass Transfer Model for Green Bean Drying

Abstract

Two diffusional models were developed for finite cylindrical shaped bodies which take into account that mass transfer could have a nonisotropic nature. In the first model, sample shrinkage was ignored; thus, it was solved by the separation of variables method. This hypothesis of constant sample volume was not assumed in the second model, which solved mass transfer equations through a finite difference scheme. The proposed models were applied to the simulation of drying curves of green beans (Phaseolus vulgaris). Two different effective diffusivity coefficients, one radial and the other axial, as a consequence of the mass transfer through both directions, were estimated in each model. The effective diffusivities estimated with the proposed models varied with the temperature according to the Arrhenius law. The average percentage of variance explained by the fixed boundaries model was 96.1% and increased to 99.1% when shrinkage was considered (in the model solved by a finite difference method). Keywords: Drying models; nonisotropic mass transfer; green bean; shrinkage