Effect of Charging State of Particles on Electret Filtration

Abstract

Collection performance of an electret filter with rectangular fibers was studied experimentally for cases in which electrostatic effect and Brownian diffusion are predominant by using particles from 0.02 to 0.4 ym in diameter and at different charging states. A single fiber collection efficiency qEl, was found to be expressible as a function of dimensionlegs parameters of Peclet number Pe, and Coulombic and induced force parameters, K c and K I,, as, here, A, B, C, and 1) are the numerical constants depending upon the charging density of electret fiber. Indices of each dimensionless parameter determined through the experiment coincided with the previous theory. A maximum penetration of particles appeared in the transition region of predominant collection mechanisms, i.e., between Brownian diffusion and induced force effect, ranging smaller than 0.1 pm in diameter for uncharged particles, and between Coulombic and induced force effects, ranging larger than 0.1 pm in diameter, for charged particles. Semiempirical expressions for a single electret fiber collection efficiency and a most penetrating particle size, applicable to particles in any charging state, were obtained taking account of Brownian diffusion, and induced and Coulombic force effects simultaneously. Undulation of the penetration observed in the filtration of particles in charge equilibrium was explained by using the semiempirical expression for a single fiber efficiency and charge distribution on a particle.

Experimental Study of Electrostatic Aerosol Filtration at Moderate Filter Face Velocity

“…The surface charge density that gave good agreement with experimental data was 1.2 × 10 −4 C/m 2 . This value is similar in magnitude to values given by other researchers (1.8 × 10 −5 -6.11 × 10 −3 C/m 2 ; Kanaoka et al 1987;Lathrache and Fissan 1987;Siag et al 1994;Wang 2001;Sae-Lim et al 2006;Wei et al 2006).…”

“…When both filter and particle are charged, there is a purely Coulombic force in addition to an induced electrostatic attraction. These are difficult to differentiate since the polarization force is always present to some degree (Kanaoka et al 1987). Figure 8b shows collection efficiency data for a filter face velocity of 1.5 m/s.…”

“…Lee et al (2002) concluded that theoretical models did not match experimental data because of a significant increase in charge density. A review of other studies shows assumed charge density values vary by several orders of magnitude (Lathrache and Fissan 1987;Wang 2001;Sae-lim et al 2006;Huang et al 2007;Kanaoka et al 1987). Higher fiber charge density has been seen to decrease filter penetration (Wei 2006).…”

Intermediate Air Filters for General Ventilation Applications: An Experimental Evaluation of Various Filtration Efficiency Expressions

“…The MPPS for charged synthetic filters was observed in the size interval 40-100 nm, as found also by Kanaoka et al (1987), Lore et al (2011), Rengasamy and Eimer (2011); The MPPS for glass fiber filters was observed in the size interval 100-200 nm, as determined also by Fisk et al (2002), Hinds (1999) and Hanley et al (1994). The filter samples were challenged by the neutralized DEHS aerosol in the full-scale test rig.…”

Influence of Low-Temperature Plasma Treatment on The Liquid Filtration Efficiency of Melt-Blown PP Nonwovens in The Conditions of Simulated Use of Respiratory Protective Equipment

“…When discussing the efficiency of electret nonwovens, it is important to realise the main mechanisms influencing the movement of a particle in the close proximity of a fibre, which translates directly into the probability of its capture by the filter (Barrett and Rousseau, 1998;Brown, 1993;Gougeon, Boulaud and Renoux, 1996;Kanaoka et al, 1987;Pich et al, 1987). In case of penetration of fine particles that are particularly harmful for respiratory system, it is precisely the Coulomb's interaction that is of particular significance (Martin and Moyer, 2000).…”