Penetration of Monodisperse, Singly Charged Nanoparticles through Polydisperse Fibrous Filters

Abstract

The article presents experimental results and theoretical analysis of aerosol nanoparticle penetration through fibrous filters with a broad fiber diameter distribution. Four fibrous filters were produced using the melt-blown technique. The analysis of the filters' SEM images indicated that they had log-normal fiber diameter distribution. Five kinds of proteins and two types of silica particles were generated by electrospraying and were then classified using a Parallel Differential Mobility Analyzer to obtain well-defined, monodisperse, singly charged challenge aerosols with diameters ranging from 6.3 to 27.2 nm. Particle penetration through the filters was determined using a water-based CPC. Experimental results were compared first with predictions derived from the classical theory of aerosol filtration. It is demonstrated that it is inappropriate to apply it to the arithmetic mean fiber diameter, as this results in turn in a huge underestimation of nanoparticle penetration. A better, but still unsatisfactory agreement is observed when that theory was used together with the pressure drop equivalent fiber diameter or when the Kirsch model of nonuniform fibrous media was applied. We show that the classical theory applied to any fixed fiber diameter predicts a stronger dependence of nanoparticle penetration on the Peclet number as compared to experimental data. All these observations were successfully explained by using our original partially segregated flow model that accounts for the filter fiber diameter distribution. It was found that the parameter of aerosol segregation intensity inside inhomogeneous filters increases with the increase in particle size, when the convective transport becomes more pronounced in comparison to the diffusive one.

Filtration Properties of Nanofiber/Microfiber Mixed Filter and Prediction of its Performance

“…Matulevicius et al (2014) experimentally measured the collection performance of nanofiber filter media fabricated by electrospinning of polyamide, and reported that the filter with finer fibers had a high collection efficiency and a high quality factor. Sambaer et al (2014) and Podgorski et al (2011) introduced the inhomogeneity factor in the prediction of collection efficiency of a laminated nanofiber filter, which was originally proposed by Kirsch et al (1975), and reported that the predicted collection efficiency agreed well with the experimental data by the correction with the inhomogeneity factor. They also reported that the inhomogeneity factor of nanofiber filter was high compared to HEPA filters.…”

Filtration Performance Against Nanoparticles by Electrospun Nylon-6 Media Containing Ultrathin Nanofibers

“…Podgorski (2009) derived a numerical method to compute the penetration of nanoparticles through inhomogeneous fibrous filters from single fiber filtration expressions corresponding to the Kuwabara flow (Kuwabara 1959). Good agreement was demonstrated in comparison with the experimental data when a proper segregation intensity for the different fibers was used (Podgorski et al 2011). However, the above models were not developed for the net structure of UNFs and the co-existing NFs, which can lead to special characteristics on the filtration performance.…”

Separation of Nanoparticles from Air Using Melt-Blown Filtering Media

“…The deposition efficiency for an individual fiber with a diameter d F for a diffusion mechanism E D can be calculated based on numerous correlations described in various sources (Natanson, 1957;Stechkina and Fuchs, 1966). However, the best results were obtained from the relationship that was a combination of correlations from the quoted works which took the following form (Podgórski et al, 2011):…”

“…The influence of a number of very important factors on the course of the nanofiltration process was tested, including the size of aerosol particles, their morphology, the velocity of aerosol flow through the filter and the structure of the separating material. In addition, the obtained data were interpreted using the classical theory of filtration (Hinds, 1999), which states that the Brownian diffusion is the dominant mechanism for determining the filtration efficiency of nanoparticles, and the Partially Segregated Flow Model (Podgórski, 2009;Podgórski et al, 2011;Jackiewicz et al, 2013) proposed by our research group. Up to now, the model was examined whether it can be used to describe the process of separation of sub-micron and micron-sized solid particles and monodisperse nanoparticles.…”