Heat and Mass Transfer and Breakage of Particles in Drying Processes

ISSN： 0737-3937

Source： Drying Technology, Vol.27, Iss.7-8, 2009-07, pp. : 870-877

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Abstract

An advanced theoretical model of unsteady coupled heat and mass transfer and breakage of wet particles in two-stage drying processes is presented. The numerical simulations of drying of silica slurry droplets have shown that both temperature and mechanical stresses emerge in the wet particle during drying. It has been found that mechanical stresses play a substantial role at the beginning of the second drying stage, whereas the thermal stresses are much more considerable at the end of drying. In addition, tangential stresses in the crust of wet silica particles are predominant over the radial component (approximately five times greater). Compared to the proposed breakage criterion, the model predicts that the total stresses can be a reason for wet particle cracking/breakage and this depends on granule diameter, drying agent temperature, and size of primary particles. To prevent granule breakage at given drying conditions, the slurry droplets with primary particles as small as possible are recommended for drying.