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.
Over the last few years, expectations have grown for the development of appropriate materials for separation of nanoparticles of different morphologies from air. Therefore, the objective of this work was to conduct a broad study of the process of filtration of polydisperse nanoaerosols in materials of our design and production. They were made using the modified melt-blown technology, a very promising technique that allows to produce large amounts of fibers with a wide range of diameters which when properly formed in mats or cores can be used in various filtering products, such as protective masks, car filters. The filtration efficiency for KCl solid nanoparticles and DEHS (di-ethyl-hexyl-sebacat) liquid nanoparticles in three polypropylene filters of different morphologies have been established. The obtained results show how the aerosol face velocity and the morphology of the nonwoven media affect the filtration efficiency and pressure drop. It turned out that fibrous filters of our own production can separate particles with very small diameters from the air. As the effectiveness of the separation grew with a decrease in diameter of filter fibers, a filter composed of nanoscale fibers proved to be the most effective. An increase in aerosol flow velocity through the filter negatively affected its filtering effectiveness. The observation of data for cubical KCl and spherical DEHS particles, showed no differences in filtering effectiveness, which proves that for the tested diameter range the morphology of particles removed from air does not play a significant role, as it does for larger particles. The results obtained from the filtration of polydisperse nanoaerosols were successfully interpreted using our Partially Segregated Flow Model which takes into account the polydisperse distribution of fiber diameters in the filter. What is more, it shows that the application of the classical theory of filtration significantly overvalues the results obtained in our experiments.
It is well known that diesel fumes are carcinogenic to humans and may cause inflammation of the respiratory tract, cardiovascular problems, etc. Diesel exhaust particles (DEPs) occurring in diesel fumes are fractal-like aggregates with diameters ranging between 10 and 2000 nm, with various compounds adsorbed on their surface. The fractal-like structure of DEPs and their nanosize leads to the problem of theoretically predicting the DEPs' filtration efficiency. Thus, experimental studies on effective protection against DEPs as well as theoretical modeling are essential. This study analyzes both experimentally and theoretically the mechanical and electret filters and their potential effectiveness in the filtration of DEPs. The theoretical analysis of the filtration process on fibrous fabrics was performed using classic filtration theory, assuming that the filtration layer can be treated as a system of a single fiber located in the Kuwabara cell. The experimental results show that the fibrous filters, produced using melt-blown technology, provide a high level of protection against DEP aerosols (93 %-99 %). The obtained filtration efficiencies are (in some cases) even higher than requested for particulate respiratory half-mask type 2 (made from a fibrous filter). However, the theoretical results obtained using classic filtration theory indicate lower filtration efficiencies than the experimental ones.
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