Removal of fine particles on fibrous filters: A review

Fibrous filters have long been recognized as an efficient means of removing aerosol particles from the carrier gas or air stream. There are various mechanisms by which the aerosol particles are captured on a filter material, and these include interception, inertia, diffusion, electrostatic attraction, and gravity. The aerosol particle size and filter properties determine the removal mechanisms that dominate for a particular filtration application. This chapter gives a review of removing fine particles on fibrous filters. Many theories have been developed to describe the particle interaction with the surface of the filter and to estimate the probability of the particle adhesion onto a surface. The collection efficiency of a fibrous filter depends on the structure of the filter (porosity, fiber diameter, and filter thickness), the operational conditions (filtration velocity, temperature, and humidity), and, in particular, the filtering aerosol characteristics (particle density, size, and shape). The possibility of the particle bouncing depends on its composition, its shape, its velocity, and the type of impaction surface. When a solid particle contacts a surface at low velocity, the particle loses its kinetic energy by deforming itself and the surface. At higher velocities, part of the kinetic energy is dissipated in the deformation process (plastic deformation) and part is converted elastically to kinetic energy of rebound. If the rebound energy exceeds the adhesion energy-the energy required to overcome the adhesive forces-a particle will bounce away from the surface. When the materials comprising the particle and surface become harder, the particle becomes larger, or its velocity becomes greater, then the likelihood of the particle bouncing from the surface also becomes greater.