Effective diffusion coefficient and mathematical modeling for drying of crambe seeds

The mechanism of the water diffusion in agricultural products is complex due to the diversity of chemical composition and physical structure of the products. The aim of this work was to fit different mathematical models to the drying process of the crambe seeds (Crambe abyssinica), under varying conditions of air and to determine the effective diffusion coefficient and obtain the activation energy. Crambe seeds harvested with moisture content of 0.26 (decimal d.b.) and dried until 0.09 (decimal d.b.). Drying was carried out under different conditions of controlled temperature 30, 40, 50, 60 and 70 degrees C and relative humidity of 37.4; 22.3; 14.0; 8.3 and 5.1%, respectively. Among the models that presented the best fit for the experimental data, Wang e Singh was the best fit to the data at different drying conditions. The effective diffusion coefficient increased with increasing temperature with values of 0.88 x 10(-11); 1.99 x 10(-11); 2.90 x 10(-11); 3.48 x 10(-11) and 5.85 x 10(-11) m(2) s(-1), for temperatures of 30, 40, 50, 60 e 70 degrees C, respectively, during crambe drying. The relationship between the effective diffusion coefficient and drying temperature can be described by the Arrhenius equation, which presents an activation energy for liquid diffusion in the drying of 37.07 kJ mol(-1).