Axial and radial moisture diffusivity in cylindrical fresh green beans in a fluidized bed dryer with energy carrier: Modeling with and without shrinkage

Drying of fresh green beans of different lengths was studied in a pilot-scale fluidized bed dryer at different air input temperatures in the range of 30-70 degrees C in presence or absence of glass beads acting as energy carriers. The experimental drying curves were adjusted to the diffusional model of Fick's law for infinite and finite cylinder with and without consideration of shrinkage to measure axial and radial effective moisture diffusivities. Radial and axial diffusivities (D-ref and D-zef) of cylindrical green beans were estimated considering experimental measurement uncertainties in different temperatures. The calculated values of diffusivity by considering shrinkage (D-efy) were smaller than the values of diffusivity without considering shrinkage (D-efx). Also axial diffusivity values estimated were always much higher than radial diffusivity values. An Arrhenius type dependence was observed between effective moisture diffusivities and drying temperature. (C) 2007 Elsevier Ltd. All rights reserved.