Simulation of aerosol agglomeration in the free molecular and continuum flow regimes

The formation of high temperature aerosol agglomerates is simulated by following the Langevin trajectory of each particle with the boundary condition that the particles stick upon collision. Both the free molecular and continuum flow are treated. A new derivation of the friction force of an agglomerate in the continuum limit is developed based on the evaluation of the surface momentum flux at the Oseen flow limit. The agglomerates can be described as a fractal, at least in regard to the power law relationship between mass and size, with a dimensionality of 1.7–1.9 independent of the flow regime. The particle growth is shown to be much more rapid in the free molecular regime than in the continuum. The global kinetics are shown to be consistent with a similarity analysis of the coagulation equation with a modified coagulation coefficient. Comparison between the simulation and coagulation theory at small time suggests a slight fluctuation enhancement in the free molecule case and a small-time enhancement of the coagulation rate at high concentration for the continuum case.