Analytical solution of mass transfer equation considering shrinkage for modeling food-drying kinetics

In order to obtain a simplified equation for the mathematical description of drying kinetics, an analytical solution of a mass transfer equation with concentration-dependent shrinkage and a constant average water diffusivity was proposed. Experimental drying curves of 4x4 cm(2) mango slices, with 0.5, 1.0 and 1.5 cm thicknesses and 10 cm long cassava parallelepipeds with 1, 2 and 3 cm thicknesses, at different air temperatures (50 degrees C: 60 degrees C and 70 degrees C) and 3 m/s of air velocity, were obtained in order to fit the proposed model by non-linear least-squares. The proposed model solutions reproduced with moderate accuracy the numerical solution of mass transfer equation, and the experimental drying curves with r(2) = 0.92 for mango and 0.97 for cassava. An evident deviation from experimental behavior was observed at moisture contents below 5% in a semi-log scale. Using the average water diffusivity and shrinkage obtained with the proposed model, an accurate simulation of experimental drying curves was obtained at low-air velocities (0.5 and 1.75 m/s). (C) 2000 Published by Elsevier Science Ltd. All rights reserved.