Kinetics of forced convective air drying of potato and squash slabs / Cinética del secado de rodajas de patatas y calabacin con corriente de aire

Abstract

Moisture content, temperature, and surface area variations of potato and squash slabs were measured during forced convective air drying; the effect of the initial moisture content on drying behaviour was also investigated. A mathematical model that numerically integrated the diffusion equation and the thermal balance for a three-dimensional shrinking 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 pre- exponential 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. Diffusion coefficients were independent of their moisture content within the range studied for both products. The activation energies for potato 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 potato took place at moisture levels around 0.4 kg water/kg dry solid, but this was not the case for squash. The differences were mainly attributed to the different shapes of the sorp tion isotherms.