(74a) Transition from Dilute to Concentrated Conditions

During aerosol synthesis of nanosized silica at industrial conditions a transition from dilute to concentrated particle loading takes place, changing the flow conditions and particle dynamics in the reactor. The formation and growth of primary particles and agglomerates is studied theoretically by accounting for gas phase chemical reaction, coagulation, and sintering of particles by neglecting the spread of the particle size distribution. The internal aggregate structure is defined by distinguishing between non-agglomerate, hard-agglomerate and soft-agglomerate structures at different stages of particle growth. The effect of maximum flame temperature and cooling rate on the effective agglomerate volume fraction of hard- and soft-agglomerates is investigated. It is shown that for the production of nanosized primary particles the effective volume fraction of the agglomerates increases so much that shear induced coagulation, restructuring and fragmentation of soft-agglomerates become important.