Influence of Particle Charge on the Collection Efficiency of Electrified Filter Mats

Abstract

A quantitative determination of the electrostatic effects on aerosol filtration is difficult since currently available methods do not provide direct measurements of coulombic and polarization parameters. This paper presents an experimental approach to determine the effects of both coulombic and polarization forces on the particle collection efficiency of filter mats. Two filter mats were tested against submicron aerosols to determine the effect of particle charge on the filtration efficiency with and without a polarizing electric field at two face velocities: 5 and 15 cm/s. The challenge aerosols consisted of either solid particles or liquid droplets in the size range 0.4 to 1.0 μm in aerodynamic diameter either in electrostatically charged or in Boltzmann charge distribution conditions. An Electrical Single Particle Aerodynamic Relaxation Time (E-SPART) analyzer and a Differential Mobility Analyzer (DMA) were used for measuring size and charge distributions of aerosol particles at the upstream and downstream of the filters. Experimental data show that measured single fiber efficiency due to electrical effects increased by factors ranging from 5 to 12 depending upon the electrostatic charge and electrical field involved. Particulate penetration in the submicron range decreased exponentially as a function of the electrostatic filtration parameter KEO defined by the ratio of electrical migration velocity to the face velocity.