The effect of particle charge on penetration in an electret filter

Experiments were performed to identify collection mechanisms for 0.5 mu m diameter particles in electret filter media and to determine the effect of particle charge on penetration. Highly monodisperse polystyrene particles were charged to various levels, and their penetration through charged to various levels, and their penetration through charged and discharged electret filters was measured with an optical particle counter. Particle penetration through charged filters was significantly lower than through discharged filters. Also, in charged filters large decreases in penetration were observed with increasing particle charge, while in discharged filters much smaller decreases occurred. Based on these results it is concluded that electrophoresis played a dominant role in the collection of charged particles, dielectrophoresis was important only at very low charge levels, and mechanical collection processes were relatively unimportant. The experimental data were compared to theoretical penetration predictions of R.C. Brown (1981). Although measured values of penetration were found to be significantly higher than those calculated from theory, the data show a systematic dependence on a single dimensionless parameter that is predicted by theory.>