English

Abstract

The goal of this work was to fit several mathematical models to the experimental data from the drying of sorghum (Sorghum bicolor [L.] Moench) grains of the AS4620 cultivar, to determine and evaluate the effective diffusion coefficient, to obtain the activation energy and to determine the thermodynamic properties of the drying process at different temperatures and air speeds. The initial moisture content of 0.228 ± 0.003 on a dry basis (d.b., decimal), were subjected to drying in an experimental dryer where the drying air speed was kept at either 0.5 or 1.0 m s-1, and for each speed, the system was set to heat at 40, 50 and 60°C until the moisture contents reached 0.137 ± 0.004 (d.b.). The Page model was selected to represent the drying phenomenon. The effective diffusion coefficient of the sorghum grains increased as temperature and air speed increased, and the pattern can be described by the Arrhenius equation, which provides activation energy values for liquid diffusion in the sorghum drying process of 27.12 and 42.05 kJ mol-1 for air speeds of 0.5 and 1.0 m s-1, respectively. When the drying temperature is increased, enthalpy and entropy decrease, whereas Gibbs free energy increases.   Key words: Mathematical modeling, activation energy, enthalpy, entropy, Gibbs free energy, Sorghum bicolor [L.] Moench, drying.