Role of product shrinkage in drying rate predictions using a liquid diffusion model

Abstract

Most real materials shrink during drying. The degree of shrinkage and its variation with drying conditions as well as product moisture content influences the mechanicms of heat and mass transport within the material. In the most commonly employed liquid diffusion model it is customary either to exclude shrinkage effects or to include them only in terms of a change in the physical domain for application of the diffusion equation and boundary conditions. The objective of this communication is to show quantitatively the effect of shrinkage on predictions of the drying rate and product surface temperature using a one dimensional liquid diffusion model. It is shown that literature values of the moisture diffusivity do not take into account the thickness change during and hence predictions using the realistic physical shrinkage lead to incorrect estimates of the drying rate. Typical results are presented using a potato slab as a model object dried convectively at low temperatures. © 2003 Elsevier Science Ltd.