A model was developed to predict the behavior of non-woven filters clogged during the filtration of nanostructured particles (i.e. agglomerates of nanometric particles). It estimates the evolution of the pressure drop and the collection efficiency during particle loading. It takes into account the filter characteristics (thickness, packing density, Davies diameter and mean fiber diameter), the particle-size distribution and the operating conditions (filtration velocity, temperature…). Only one adjustable parameter (bo) is needed, which ranges from 0.7 to 1 times the ratio of the mean fiber diameter and the Davies' diameter of the clean filter. In comparison with experimental data, the model allows satisfactorily predicting the performances (pressure drop and efficiency) of several mono or dual layer fibrous filters during particle loading.
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.
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