NONISOTROPIC MASS-TRANSFER MODEL FOR GREEN BEAN DRYING

Two diffusional models were developed for finite cylindrical shaped bo dies which take into account that mass transfer could have a nonisotro pic 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 solv ed mass transfer equations through a finite difference scheme. The pro posed models were applied to the simulation of drying curves of green beans (Phaseolus vulgaris). Two different effective diffusivity coeffi cients, one radial and the other axial, as a consequence of the mass t ransfer through both directions, were estimated in each model. The eff ective diffusivities estimated with the proposed models varied with th e temperature according to the Arrhenius law. The average percentage o f variance explained by the fixed boundaries model was 96.1% and incre ased to 99.1% when shrinkage was considered (in the model solved by a finite difference method).