Modeling Small Cluster Deposition on the Primary Particles of Aerosol Agglomerates

ABSTRACT

Dense particles, such as the primary particles in aerosol agglomerates, are formed by coagulation with rapid coalescence, or by condensation-like growth. This latter mechanism is explored in a new model. It uses the discrete-sectional model to describe the evolution of the particle mass distribution. In addition, new equations are used to describe the formation of primary particles. Primary particles are “born” when a new particle is formed above a critical size D _melt. Particles smaller than D _melt are assumed to be liquid-like, sintering rapidly in the available time. Changes in the final primary particle size D_p can be attributed to growth from small particle deposition. This growth increases as the monomer source rate decreases. For conditions representative of TiO₂ formation from chloride in a tube reactor, D_p /D _melt ranges from 1.5 to 3. When D _meit decreases, as would be expected if temperature decreases, D_p /D _melt increases. The result is that D_p is much less sensitive to temperature than would be expected from simple sintering models.