Abstract
This paper provides an overview of recent studies on the filtration of airborne nanoparticles. Classical filtration theory assumes that the efficiency of nanoparticle adhesion is at unity when nanoparticles strike a filter with a Brownian motion. However, it has been pointed out that small nanoparticles may have a sufficiently high impact velocity to rebound from the surface upon collision, a mechanism called thermal rebound. According to thermal rebound theory, the adhesion efficiency of nanoparticles decreases if their size is reduced. However, this phenomenon has not yet been clearly observed in experimental studies; there are still a number of uncertainties associated with the concept of thermal rebound, which is yet to be either proven or disproven. This review paper discusses the findings in the current literature related to thermal rebound theory.
Highlights
Nanoparticles are particles with at least one dimension less than 100 nm
The penetration of a sub-10 nm NaCl particle through the diffusion battery was measured, and the results showed that the single-fiber efficiency predicted by Kirsch and Fuchs (1968) agrees well with that measured in the experiment, which was based on consideration of the equivalent fiber diameter of the diffusion battery (Gómez et al, 2012)
The results showed for sub-100 nm particles, that filtration efficiency is independent of relative humidity, because capillary force has no effect on nanoparticles adhesion (Kim et al, 2006)
Summary
Nanoparticles are particles with at least one dimension less than 100 nm. Airborne nanoparticles are sometimes referred to as nanoaerosols and ultrafine particulate matters. Recent studies have pointed out that those small nanoparticles striking a filter surface could rebound if the amount of initial kinetic energy in the approaching particle surpasses that of the adhesion energy between the particle and the surface (Dahneke, 1971; Wang and Kasper, 1991). In the last few decades, there have been a great amount of publications that focused on nanoparticle filtration and thermal rebound Advances in these areas of research deserve a systematic overview. Theoretical methods of calculating single-fiber efficiency for nanoparticles are first presented, followed by an examination of the effects of numerous parameters, such as humidity, particle shape, and fiber diameter, on nanoparticle filtration efficiency. Calculation of Nanoparticle Filtration Efficiency Classical theory to calculate the filtration efficiency (η) is expressed as a function of single fiber efficiency (E) (Hinds, 1999): exp
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