LAUSR

Abstract The absorption of sulfur dioxide by an atmospheric circulating drop was numerically investigated at low Reynolds number. The effects of Reynolds number and solid nucleus (spherical) on sulfur dioxide absorption were particularly focused in the present study. Mass transfer of sulfur dioxide of a pure water drop was simulated by utilizing radial diffusion and internal vortex mechanisms. With an increased Reynolds number, the sulfur dioxide transport via internal vortex is significantly enhanced. Sulfur dioxide, with the lowest concentration, moves from drop center, through the centerline, and towards the vortex center. Meanwhile, vortex strength in the drop gradually decreases as the solid nucleus grows and also due to flow retardation effect at solid surface. For drop film with relative thickness of λ = 0.5, internal circulation significantly affects the sulfur transport process. The lowest concentration point is located at the front stagnation point of the solid particle. In contrast, rear stagnation point hosts extra sulfur dioxide by convection (besides pure radial diffusion) which is originated from solid surface retardation. For drop film with relative thickness of λ = 0.3, the strength of internal circulation is reduced, but still affects sulfur dioxide transport to a lesser extent. With drop film further decreases to λ = 0.1, absorption of sulfur dioxide is almost only controlled by radial diffusion, as the particle is so large that, the one-dimensional diffusion through liquid film is gaining significance when compared with internal convection. The thickness of drop film obviously affects strength of internal circulation and the sulfur transport.