(201g) Modeling Air-Borne Nanoparticle Diffusion Through Filters

Nanoparticles are being used in many commercial products and this increases the chance of release of nanoparticles to the environment. Air filtration can be an effective way to remove nanoparticles from the air stream. Due to the small size and mass, diffusion is the dominant filtration mechanism for nanoparticles, and the total collection efficiency will be close to collection efficiency due to diffusion only. The objective of this study is to perform numerical simulation of air-borne nanoparticle diffusion across filters using commercial computational Fluid dynamics model (CFX, ANSYS).

The model methodology was first verified with the case of nanoparticle penetration across standard screen filter, which has a highly regular and repeating cross-shaped configuration. The modeling results agree well with the experimental findings reported in the literature. The method is then extended to real filters. The 3-dimensional geometries of filters are constructed based on electron microscopy observations. Calculations show that filters are very efficient in trapping particles if only concentration-gradient-driven diffusion (zero air flow) is considered. In the case of convective diffusion, when a finite air flow is allowed to pass through the medium, particle penetration increases. The change in penetration is a function of face velocity of the air flow. Details of the simulation results and their comparison with experiments will be discussed.