Size Distribution Evolution of Fine Aerosols Due to Intercoagulation with Coarse Aerosols

Controlling the emission of submicron particles of toxic metals in a combustion system poses a challenge. One possible mechanism for removing these fine particles is through intercoagulation with coarse particles. A bimodal lognormal model was applied to investigate the impact of intercoagulation rate on the size distributions of fine-mode aerosols. Fine-mode particle removal time was found to depend strongly on the number concentration of coarse-mode particles, but it was independent on the number concentration of fine-mode particles. An increase of geometric standard deviation of fine-mode particles from 1 to 1.6 significantly increased the dimensionless removal time 27 times. On the contrary, an increase of the deviation of coarse-mode particles in the same range only decreased 3% of the dimensionless removal time. The variation of geometric mean size ratio, meanwhile, had only insignificant effects on dimensionless removal time. For a constant mass concentration, removal time decreased as geometric standard deviation narrowed and mean size of coarse mode decreased. Fine-mode particles ultimately approached monodisperse when the dominant mechanism was intercoagulation; meanwhile, coarse-mode particles approached the asymptotic shape because intracoagulation was the dominant mechanism. The results show that on a constant mass basis, monodisperse coarse-mode particles with a high number concentration are the optimal condition for enhanced removal of fine-mode particles through intercoagulation.