SINGLE-FIBER COLLECTION AND ADHESION EFFICIENCY FOR BIOLOGICAL PARTICLES

Good efficiency of fibrous filters requires not only single fibre coll ision efficiency but also single fibre adhesion efficiency. Especially at higher filtration velocities (>0.5 m/s) and for larger particles ( >5 mu m), particles may not adhere to the fibres after impact but rebo und off the fibres. The particle bounce mechanisms on filter fibres ar e rarely investigated, particularly for biological particles (fungal s pores, pollen) which are in the size range where particle bounce is do minant. With a special measuring device working with a modified optica l particle counter, single fibre collection efficiencies could be dete rmined for various biological and non-biological particles and fibre m aterials. The results reveal that the single fibre collection efficien cies for biological and non-biological materials are very similar and increase with increasing Stokes number to a maximum value of about 0.4 5. Beyond a Stokes number of about 2, the single fibre collection effi ciency decreases with increasing Stokes number, indicating particles b ouncing oft the fibres, A comparison of the experimentally determined collection efficiencies with published theoretical considerations show ed insufficient agreement, suggesting that the properties of the parti cle materials do not significantly affect the adhesion efficiency. Bas ed on the experimental results, a mathematical correlation for the sin gle fibre collection efficiency was derived which allows a more accura te prediction of the collection efficiency of fibrous filters.