We designed and modelled a fluidized bed dryer. Based on the literature, modelling of a bed dryer is carried out for two situations: for spherical and non-spherical particles. Two case studies were taken from the literature for modelling the fluidized bed dryer for naphthalene balls and mushroom slices. Fluidized bed dryer design was carried out with respect to diffusivity of the bed materials. Drying characteristics in terms of effective diffusivity were studied for naphthalene balls and mushroom slices using a tapered fluidized bed dryer. The variation of effective diffusivity was obtained with change in inlet air temperature, velocity, thickness of slab and drying time. Experimental effective diffusivity as obtained from literature was compared with model predicted values, provided lower deviations with RMSE of less than 8.28% for spherical naphthalene balls and 0.936% for the mushroom slices. Mass transfer coefficient obtained for naphthalene balls was in the range of 2.1×10-4 to 4.857×10-3 m sec-1. The diffusivity constant was evaluated using Fick's diffusion equation assuming surface moisture in equilibrium with the surrounding atmosphere. The value of diffusivity constant (D0) obtained is 1.828×10-9m2sec-1 and the value of activation energy (Ea) obtained is 4.523 kJ mol-1.