The role of electric forces in the filtration of aerosols by fiber filters

Abstract

The net electric charge on the fibers of various filters and the electric charge distributions of typical test aerosols were measured. A simple theory of filtration which included electric as well as mechanical effects was developed in order to apply these data to appropriate filtration results. Most fibers have an electric charge, even though it may be very small. When the test aerosol in filtration experiments is a homogeneous uncharged aerosol from a La Mer-Sinclair generator, a peak in the per cent penetration versus particle radius curves appears at approximately 0.05 μ, depending on the velocity of the air through the filter. The presence of electric forces of induction decreases the penetration of large particles and tends to decrease the radius at which maximum penetration occurs. When the aerosol used is a heterogeneous aerosol produced by any of the normal means, the peak in the penetration versus particle radius curves appears at larger values of the radius, depending upon the net electric charge per unit length of the fibers and the electric charge distribution of the test aerosol. It is pointed out that some unexplained filtration results may be due to some of the aerosol particles' escaping capture on contact. No attempt was made to assess the part played by electric forces in ensuring adhesion on contact.