Aerosol filtration by means of Nuclepore filters: structural and filtration properties

By combination of a differential mobility analyzer (DMA) with a filter with uniform pores, namely a filter sensor, a new method for differentiating nanoparticles with various mass-mobility fractal dimensions, D fm , was developed and validated experimentally and theoretically. The sensor is also able to measure the effective length (or maximum projected length) of nanoparticles with different shapes, which is an important parameter responsible for the lung deposition due to interception. At the same mobility diameter, it was observed that the compact NaCl had the highest penetration followed by partially sintered silver (Ag) aggregates and then the loose Ag and soot agglomerates. The result indicates that the stronger interception by the filter is correlated to the more elongated shape of the particles. A modified capillary tube model for predicting the penetration of Ag nanoparticles with different mass-mobility fractal dimensions was validated by experimental data. By using the validated model, this study found that the sensor could have a further enhanced sensitivity if the porosity and thickness of the filter were adjusted to 0.01 and 5 mm, respectively. The penetration differences obtained from the model are as high as 7-18%, 14-35%, and 24-40% between spheres and loose agglomerates (D fm D 2

Section: Theoretical Methodsmentioning

confidence: 99%

Optimizing Filtration Experiments for Length and Fractal Dimension Characterization of Non-Spherical Particles

Chen

Wang

Fißan

et al. 2015

“…The capillary tube models developed by Spurny et al (1969) and Manton (1978Manton ( , 1979 for spherical particle 1000 penetration through Nuclepore filters have been modified for applications to soot and Ag agglomerates in our previous works (Chen et al 2013a,b). In the models, the considered mechanisms of particle deposition included the diffusions on filter surface and inside the pore, interception at the pore opening, and impaction on the filter surface.…”

Section: Capillary Tube Modelmentioning

confidence: 99%

Carbon Nanotube Penetration Through Fiberglass and Electret Respirator Filter and Nuclepore Filter Media: Experiments and Models

Chen

Wang

Bahk

et al. 2014

Three different respirator filter media (two electrets and one fiberglass) were challenged with monodisperse multi-walled carbon nanotubes (MWCNTs) of mobility diameters 20-500 nm at 5.3 and 10.6 cm s ¡1 face velocities. The penetration data were compared with that of sphere-like NaCl particles. The MWCNT penetrations were generally lower than those of NaCl at both face velocities in all three filters. However, the MWCNTs had a slightly higher penetration than the NaCl in the fiberglass filter at 10.6 cm s ¡1 face velocity when their mobility diameters were lower than 50 nm and the alignment effect was expected to occur. Results from the scanning electron microscopic (SEM) analysis supported the hypothesis of the alignment effect, which showed that the MWCNTs tend to be straighter or with higher aspectratios at the mobility sizes less than 100 nm, leading them more readily to align with the flow. Therefore, caution should be exercised when respirators are used against the MWCNTs with the mobility diameters less than 100 nm. The single fiber theory predicted the penetration of both particles in the fiberglass filters well for the particles with below 100 nm mobility diameters but discrepancies occurred beyond 100 nm. The theory still predicted the NaCl penetration through the electret filters well for the sizes below 100 nm but only predicted the MWCNT penetration well for »20-30 nm. The Nuclepore filter and the corresponding capillary tube model were adopted to study the mechanical deposition mechanisms of MWCNTs. The model was found to predict MWCNT penetration very well when the effective length of the MWCNT was taken into account.

“…The theoretical prediction for the particle collection ef ciency of these lters has been based on models that assumed uniformly distributed arrays of equal size pores (Pich 1964;Spurny et al 1969a). The main mechanisms affecting particle capture are:…”

Section: Nuclepore Filtersmentioning

confidence: 99%

“…Only particles depositing inside the pores or on the edge of the pores are responsible for raising the pressure drop with particle loading through the Nuclepore lter. Although the expression by Spurny et al (1969a) is probably correct for particles depositing due to diffusion inside the pore, it cannot be readily applied to the case of particles depositing on the pore due to combined interception/impaction. Consequently, we decided to rst determine experimentally the effect of parameters such as particle size and density, as well as lter face velocity and pore size on the pressure drop with loading.…”

Section: Nuclepore Filtersmentioning

confidence: 99%

Experimental Investigation of Pressure Drop with Particle Loading in Nuclepore Filters

Sioutas¹

1999

ABSTRACT. This paper presents an experimental investigation of the increase in pressure drop with particle loading in Nuclepore lters. The average increase in pressure drop per unit time and particle mass concentration was measured as a function of particle size, density, and hygroscopicity. Two different Nuclepore lter pore diameters were tested (2 and 5 m m, respectively) at lter face velocities ranging from 4 to 52 cm/s.Our results showed that the increase in the pressure drop with particle loading inversely proportional to the square root of particle speci c gravity and depends weakly on particle diameter (to the power of -0.2). Furthermore, the increase in the pressure drop with particle loading is proportional to the lter face velocity and inversely proportional to the cube of the pore diameter. Particle interception and impaction on the pore edges are the main deposition mechanisms that are responsible for raising the pressure drop over time across the lter, especially for particles having Stokes numbers below 5. Particle deposition due to diffusion inside the pores is important for particles smaller than 0.2 m m. These observations agree well with previously published studies on particle deposition on the pore edges in Nuclepore lters. Our tests also showed a dramatic decrease in the pressure drop with loading for hygroscopic particles as the relative humidity increases from 10% to 50%. The pressure drop with loading decreases almost inversely proportional to the relative humidity for ammonium sulfate particles.