Removal of Nanoparticles from Gas Streams by Fibrous Filters: A Review

Abstract

Although the basic principles of fibrous filters have been well understood for capture of micron and submicron sized particles, questions arise when they are applied to nanoscale particles. In the first part of this review, the classical theory of fibrous filters is described with focus on the principles that are applicable to nanoparticle collection. The areas of recent developments reviewed include thermal rebound of nanoparticles and the effects of particle shape, aggregate morphology, flow regime, humidity, fiber size, and particle loading. One of the outstanding questions in nanoparticle collection is the particle size at which the effect of thermal rebound on collection efficiency can be observed. Theoretical calculations indicate that the effect probably can be observed only for particles smaller than 1 nm, but experimental confirmation is difficult at present because of lack of instruments for classifying and counting subnanoscale particles. Two promising devices based on filtration principles have been studied in recent years: multilayer filters and inertial fibrous filters. Multilayer filters, which are composed of nanofiber and microfiber mats, have potential to become an efficient and economical device for removing nanoparticles from gas streams. The inertial fibrous filter operates at high flow rates and relatively low pressure drop, thereby offering an attractive alternative to lowpressure impactors for nanoparticle sampling. Further development of these two types of filtration devices is needed to make them simple and reliable.

An Overview of Airborne Nanoparticle Filtration and Thermal Rebound Theory

“…Most particles and filters may carry ions; however, the level of charges is so low that affect the filtration efficiency. It has been shown that filtration efficiency of small nanoparticles is much lower for uncharged particles than for highly charged ones, because of the lower charging efficiency the discrepancy between the removal of charged and uncharged particles decreases and the electrostatic forces may not play an important role to remove nanoparticles (Wang and Otani, 2013). Thus, the effective mechanisms for removing nanoparticles with low charged level are Brownian diffusion and interception that were completely discussed.…”

Updated Correlation Between Aircraft Smoke Number and Black Carbon Concentration

“…Therefore, the FOA3 SN-C BC correlation, based on ∼100 nm BC, is inconsistent with the observed size distribution of aircraft-generated BC. It is generally understood that the filtration efficiency depends upon filter characteristics (e.g., fiber diameter, solidity, and thickness), flow rate, and particle size (Lee and Liu 1982;Wang and Otani 2013). The filtration efficiency of the specified filter for aircraft SN measurements has not previously been characterized so it is not currently possible to infer the BC mass collection efficiency for different PSDs.…”

Filtration Performance of Dual-layer Filter Paper with Fibrillated Nanofibers

“…Theoretical predictions and investigations indicate that, when the fiber diameter is less than 1 μm, the filtration efficiency of filter paper can be dramatically improved by the slip-flow effect and the huge specific surface area of ultra-fine fibers (Kosmider and Scott 2002;Ward 2005;Thakur et al 2013;Wang and Otani 2013). Grafe et al (2001) reported that nanofibers provided significant increases in filtration efficiency with a relatively small reduction in permeability.…”