Electrostatic Air Filtration by Multifunctional Dielectric Heterocaking Filters with Ultralow Pressure Drop

Abstract

In air filtration, for creating healthy indoor air, there is an intrinsic conflict between high filtration efficiency and low wind pressure drop. In this study, we overcame this conflict by developing new dielectric heterocaking (HC) filters, in which high relative dielectric constant (εr) materials were heterogeneously loaded on traditional polymer fibers. The dielectric HC filters in an electrostatic polarizing field generate a great amount of charges on their surface, leading to a strong attraction to precharged aerosol particles, and result in high filtration efficiency. Observing via a charged coupled device camera, the migration speed of aerosol smoke particles toward the polarized HC fiber exceeded those toward the unpolarized HC fiber by a factor of 6. We loaded high-εr HCs including manganese dioxide (MnO2), activated carbon, zinc oxide (ZnO), copper oxide (CuO), and barium titanate (BaTiO3) on polyurethane foams using a fast and large-scale roll-to-roll gel squeezing method. Based on the experimental results, when HCs had a εr larger than 5.1, an increased εr did not benefit electrostatic filtration efficiency for aerosol particles much, but resulted in a larger net ozone production. We suggested a MnO2-HC filter for efficient and multifunctional filtration of indoor particles, ambient ozone, and formaldehyde with only 3.8 Pa pressure drop at 1.1 m/s filtration velocity. This efficient and cost-effective dielectric HC filter opens a new avenue for the design of multifunctional filters, which will facilitate its large-scale production and commercial application in the ventilation system for healthy buildings.

Ultralow Resistance Two‐Stage Electrostatically Assisted Air Filtration by Polydopamine Coated PET Coarse Filter

“…D 2 , the distance between the two mesh electrodes in stage II, will be sufficiently long to prevent any dielectric breakdown discharge (unlike stage I). E 2 promotes 10 2 µm ranged interactions between the polymer fiber and the ( q p , d p ) particle, as well as between the particles (recall Faraday's electric field‐line experiment on forming chains of dielectric particles), [ 30 ] so it becomes easier for the particles to find a fiber surface and attach to it, as well as to agglomerate with other particles and form “dust clusters.” [ 30 ] Given that we would like to operate the filter in high air velocity mode, the dust clusters will be subjected to large shear forces, and may become resuspended if the few Å‐ranged particle–polymer adhesion is not strong enough. Thus, surface engineering of filter fibers to enhance the long‐duration adhesion (up to weeks, and even when U 1 and U 2 are turned off) between the dust cluster and fiber surface is crucial, to prevent dust cluster resuspension and enhance dust‐storage capacity.…”

“…This would enable air resistance below 10 Pa at an air filtration velocity of tens of cm s −1 , with a ≈1 cm thick, 200 g m −2 filter. (b)significant E 2 that penetrates the ≈1 cm thick filter interior to cause “Faraday agglomeration” across such ≈10 2 µm pore distance, which we have previously demonstrated with multiple dust particles being observed to form chains, using in situ optical microscopy. [ 30 ] This also requires a strong dielectric response of the fiber in the range of diameter, e.g., ≈10 1 µm. (c)a small and perhaps nonlinear electronic conductivity ( I – V relation) of the fiber to have reasonable antistatic property, [ 33,34 ] so while the monopolar charge q p of a dust particle enhances its long‐range interaction with the fiber, such monopolar charge gets released over a timescale of minutes to hours, allowing this dust particle to later dielectrically bind with other dust particles, which originally carried the same‐signed charges. (d)fiber diameter on the order of ≈10 1 µm, with the expectation that it may become 2 × or 3 × thicker with dust coverings after long‐term filtration operation. Ideally, we would like the filter to be able to trap as much dust as its own weight, meaning ≈10 2 g m −2 dust‐holding capacity.…”

“…[ 20 ] An approach to improving the performance of EAA filtration is loading high dielectric constant inorganic particles on polyurethane (PU) foams by adhesive. [ 30 ] However, this adhesive method requires base filters of large pores to avoid the adhesive blocking the airways. Since large pores would let certain particles bypass the collecting media, the highest filtration efficiency for 0.3–0.5 µm particles was less than 90%.…”

“…Since large pores would let certain particles bypass the collecting media, the highest filtration efficiency for 0.3–0.5 µm particles was less than 90%. [ 30 ] Furthermore, coating inorganic particles causes a significant decrease in filter flexibility. [ 31 ]…”

Electrostatic Precipitators as an Indoor Air Cleaner—A Literature Review

“…However, this conclusion should not be regarded as a general difference between filter-based air cleaners and electrostatic air cleaners. Tian et al [41][42][43][44] developed electrostatically assisted mechanical filters. Tian et al [45] also presented a comprehensive quality factor (CQF) to evaluate the performance of electrostatic particle removal technologies.…”