Capture of Ultrafine Particles Using a Film-Type Electret Filter with a Unipolar Charger

Abstract

Electret filters have been used widely to collect particles because of their low pressure drop and high collection efficiency due to the electrostatic attraction between the particles and filter. However, the collection efficiency of these filters decreases over time due to charge degradation. Therefore, a unipolar charger using a corona discharge was combined with an electret filter to overcome this decrease. The highest particle collection efficiency for 70 nm, uncharged particles occurred with a fresh electret filter was 34.0%, whereas a neutralized filter had a collection efficiency of 32.6%. However, when fresh and neutralized electret filters were used with a unipolar charger (electret field: 1.9 kV cm -1 ), the highest particle collection efficiencies of 99.8% and 98.2%, respectively, were obtained and appeared at the electrode-tomesh distance, a distance similar to the duct diameter. The distance between the tip of the discharge electrode and filter, which can be predicted using Sigmond's law, affected the charge density value on the filter surface. The ozone concentration was negligible under optimum conditions for particle collection. Therefore, using an electret filter combined with a corona discharge has good potential for improving air purifiers.

On the charged aerosols generated by atmospheric pressure non‐equilibrium plasma

“…Aerosols measurement by electrical low pressure impactors need particles to be charged by a corona discharge system, and the consequent faradic current generated by charged particles along each flow channel can be measured. Charging aerosols is also technical foundation for gas purification facilities such as air filtration equipment and electrostatic precipitators [8,9]. Because the unipolar charging has higher charging efficiency, and recombination of charged particles with opposite polarities can be avoided, it receives more attentions than bipolar charging for these applications.…”

Effects of solid particles with various charging states and oil aerosols on the filtration characteristics of electret media

“…Sambudi et al. 20 examined the effect of a corona charger on the collection efficiency of electret filters and verified that the initial efficiency was increased from 34% to 99.8% when a unipolar charger was used. Chang et al.…”

A novel-charged fibrous media characterized by higher efficiency and lower pressure drop

“…The other is to increase the charge capacity of the filter fibers. Promising results in enhancing filtration efficiency have been shown when escalating charge capacity of filter fibers is combined with lower pressure drops (Choi et al 2015;Li and Jo 2010;Sambudi et al 2017).…”