DRYING SIMULATION OF A SOLID SLAB WITH 3-DIMENSIONAL SHRINKAGE

A mathematical model is developed to simulate the drying of a hygroscopic porous solid. The model, based on the gradient of moisture concentration per unit Volume as driving force, takes into account the migration of water within the solid by diffusion and the evaporation at the interface. A mathematical equation for diffusion in a slab with three dimensional shrinkage has been derived, assuming that the magnitude of shrinkage is equal to the volume of water evaporated. The resulting diffusion equation and the heat balance equation for infinite thermal conductivity were solved numerically with temperature dependent diffusion coefficient and convective boundary conditions. The dependence of the desorption isotherm with temperature is also considered. Combination of all these factors in a single model provides a tool that is effective in predicting drying behavior and also useful in exploring and understanding the impact of important variables on the drying process.