BATCH FLUIDISED BED DRYING: ANALYSIS ON KINETIC MODELS

The appropriateness of the use Fick's diffusion equation to represent the falling rate drying kinetics forms subject of the present paper. Several authors have used Fick's diffusion equation to evaluate the effective diffusivity coefficient for different materials in fluidized beds. Marginal dependence of the evaluated diffusivity coefficient with the solids holdup has been reported without valid justification. Towards verifying the above, experiments are conducted in the present study by varying the solids holdup on a larger scale, by varying the fluidization column diameter. The estimated diffusion coefficient is found to vary from 2.4×10^-11 to 8.2×10^-11 for the variation solids holdup from 0.3 to 2.6kg. The inadequacy of the Fick's diffusion equation for modeling the kinetics of drying in fluidized bed is highlighted, cautioning the comparison of the kinetics often made based on the diffusion coefficients.