This investigation presents a simple model to describe defluidization time. It includes such operating parameters as operating temperature, gas velocity and number of bed particles. The proposed model also uses the plastic-viscous flow mechanism and the average convective solids mass flow rate to evaluate the adhesive and segregation forces. Mass and force balance were employed to develop the model. Then, the thickness of the coating layer was calculated by measuring the density of the agglomerate, to elucidate the coating characteristics of eutectics on the particle surface. The resulting predictions were based on a regression of our previous results. Comparing the experimental data with the predicted defluidization time reveals an error of between -20% and +20%, when the proportion of Na in the bed material was between 0.8 and 1. These data represent close agreement. (C) 2005 Elsevier B.V. All rights reserved.