An investigation on drying of millet in fluidized beds

Experiments were conducted to estimate the drying kinetics of millet in a batch fluidized bed. The drying rate was found to increase significantly with increase in temperature and with flow rate of the heating medium, while decrease with increase in solids holdup, in line with the qualitative understanding of the kinetics of drying in batch fluidized beds. Among the various popular semi empirical models tested with the experimental data, the simplest of all the models, page model was found to match the experimental data with the root mean square error (RMSE) of less than 1.4%. The effective diffusivity coefficient was evaluated using Fick's diffusion equation assuming surface moisture in equilibrium with the surrounding atmosphere, by minimizing the error between the experimental data and the model prediction. The evaluated effective diffusivity coefficient was found to vary from 0.53 × 10^-11 to 2.8 × 10^-11 with RMSE less than 3.4%. The effective diffusivity of millet is found to be approximately three times lower than that of ragi (food grain) and corn.