MODELING THE PROCESS OF DIFFUSION EVAPORATION OF A LIQUID FROM A POLYMER SPHERE, BY CONSIDERING THE SHRINKAGE OF THE SPHERE

During the process of evaporation of a liquid from a polymer, a change in dimension of the solid generally takes place. Classical models, and especially the analytical solutions of the Fick's law, are determined by neglecting this decrease in volume. A new model based on a numerical method with finite differences is built up, by taking into account not only the transfer of liquid by diffusion through the solid and evaporation from the surface but also the shrinkage of the bead resulting from the evaporation of liquid. Beads made of ethylene vinyl acetate copolymers are chosen for testing the model, because their capacity of absorption for the liquid are important, while the liquid is n-hexane. The results are expressed in terms of the kinetics of evaporation and of the profiles of concentration of liquid developed through the bead. The profiles of concentration obtained with this new model are clearly different from those obtained with the classical models neglecting the shrinkage.