KINETICS OF FORCED CONVECTIVE AIR-DRYING OF POTATO AND SQUASH SLABS

Moisture content, temperature, and surface area variations of potato a nd squash slabs were measured during forced convective air drying; the effect of the initial moisture content on drying behaviour was also i nvestigated. A mathematical model that numerically integrated the diff usion equation and the thermal balance for a three-dimensional shrinki ng slab was used to simulate the drying process. The parameters of the model (surface area, heat transfer coefficient and dry solid density) were experimentally determined. Fitting parameters (activation energy and preexponential coefficient in the Arrhenius equation) were found by comparing experimental and predicted drying curves. Good agreement was obtained down to a moisture level of 0.4 kg water/kg dry solid. Di ffusion coefficients were independent of their moisture content within the range studied for both products. The activation energies for pota to and squash were 2.09 x 10(4) kJ/kg mol and 3.76 x 10(4) kJ/kg mol, respectively. Changes in the rates of drying and heating curves for po tato took place at moisture levels around 0.4 kg water/kg dry solid, b ut this was not the case for squash. The differences were mainly attri buted to the different shapes of the sorption isotherms.