The aim of this work is to study the drying kinetic behavior with respect to the variation of the external conditions. Diffusion model based on Fick's law is used. The heated air thermo-physical properties variation and shrinking effect are taken into consideration. The coefficient of diffusion is calculated based on experimental data and presented as a function of temperature and velocity. The numerical resolution of the mass transfer equation allows the calculation of the distribution of moisture inside the product, at any time. Sudden and progressive augmentation of temperature and velocity are simulated; the drying kinetic answers by changing its behavior with a non-instant response. Solar drying was investigated through the study of a flat air collector. The ambient air velocity considerably influenced the outlet temperature of the collector air which reverberates on the drying kinetic. (c) 2005 Elsevier Ltd. All rights reserved.