The drying kinetics of forage turnips (Raphanus sativus L.)

A study aimed at determining the best mathematical model to describe the drying of forage-turnip seeds, along with the diffusion coefficient and activation energy under different air-conditions, was carried out in a randomized design with four replications. Seeds were harvested, having a moisture content of 0.36 (decimal bs) and then dried to 0.09 (decimal bs) in an experimental dryer at controlled temperatures of 30; 40; 50; 60 and 70 degrees C and relative humidities of 47.3; 26.2; 12.0; 10.1 and 5.1%, respectively. The effective coefficient of diffusion was calculated by F-test variance analysis and regression, adopting a 5% level of probability. The conclusion was reached that among the models analyzed, that of Midilli best fit the drying curves of forage-turnip seeds. The effective diffusion coefficient increases with temperature, with values of between 3.23 x 10(-11) and 10.42 x 10(-11) m(2) s(-1) for a temperature range of from 30 to 70 degrees C. The relationship between the coefficient of diffusion and drying temperature can be described by the Arrhenius equation which gives an activation energy of 24.78 kJ mol(-1) for liquid diffusion in the drying process of forage-turnip seeds.