The Role of Theoretical and Mathematical Modelling en Scale-Up

Drying processes are complex because of the non-linearity of physical phenomena and of the distributed parameter character on many levels of consideration. At different scales the relative importance of phenomena will differ. A discussion of the level structure is presented and the concept of “critical grain size” is introduced. As a general criterion for the importance of panicle diffusion resistance a modified Biot-number is defined. Theoretical models are treated for diffusional mass transfer, both rigorous and short-cut models. The integration of these models with approximating relations or models for specific drying processes is demonstrated for spray drying of foods and fluidized bed drying of bioproducts. Also a theoretical treatment of several quality aspects is given.