Association of fibrous filters for aerosol filtration in predominant Brownian diffusion conditions

In order to improve the dust retention capacity of air filters and increase their lifetime, the filtration performance of associations of fibrous filters has been investigated. This study highlighted the interest of the addition of a medium or coarse filter, composed of microfibers, upstream of a HEPA filter. Collecting nanostructured particles in the depth of this upstream filter, rather than directly on the surface of a HEPA filter, permits to significantly reduce the pressure drop increase while maintaining a global mass collection efficiency close to the unit. On the one hand, the association of a medium filter and a HEPA filter induces a real energy gain, compared to the implementation of a single HEPA filter. On the other hand, the implementation of a coarse filter, presenting a too low initial collection efficiency, upstream of a HEPA filter leads to mixed results.