Lucija Boskovic

Influence of Particle Shape on Filtration Processes

The influence of particle shape on filtration processes was investigated. Two types of particles, including spherical polystyrene latex (PSL) and iron oxide, and perfect cubes of magnesium oxide, were examined. It was found that the removal efficiency of spherical particles on fibrous filters is very similar for corresponding sizes within the range of 50–300 nm, regardless of the fact that the densities of PSL and iron oxide differ by a factor of five. On the other hand, the removal efficiency of magnesium oxide cubic particles was measured, and found to be much lower than the removal efficiency for the aerodynamically similar spheres. Such disparity was ascribed to the different nature of the motion of the spherical and cubic particles along the fiber surface, following the initial collision. After touching the fiber surface and before coming to rest, the spherical particles could either slide or roll compared to the cubic ones, which could either slide or tumble. During tumbling, the area of contact between the particle and the fiber changes significantly, thus affecting the bounce probability, whilst for the spheres, the area of contact remains the same for any point of the particle trajectory. The extra probability of particle bounce by the cubes was derived from the experimental data. The particle kinetic energy was proposed to be responsible for the difference in removal efficiency of particles with alternative shapes, if all other process parameters remain the same. The increase in kinetic energy is shown to favor the increase of the bounce probability.

Removal of Fine Particles on Fibrous Filters: A Review

Publisher Summary 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.

CHAPTER 13 – Removal of Fine Particles on Fibrous Filters: A Review

Publisher Summary 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.

Removal of Fine Particles on Fibrous Filters

Publisher Summary 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.