Abstract
Thermal rebound of nanoparticles on the surface of fibers is of big concern in collecting nanoparticles. Another factor influencing the collection of nanoparticles is the inhomogeneity of fiber packing. The present work studied the influence of filter inhomogeneity on the collection efficiency of nanoparticles by using wire screens as uniform structure in comparison to real filters. As a result, the single fiber collection efficiencies of nanoparticles through wire screens are in good agreement with those predicted by Kirsch and Fuchs (ηD=2.7Pe(superscript -2/3)), but the dependence of real filters on Pe is somewhat smaller than –2/3 and in agreement with (ηD=0.84Pe^(-0.43), Wang et al., 2007). The dependence of single fiber collection efficiency on Pe for the real filters is well explained by considering non-uniformly packed filter consisting of two regions of densely packed and loosely packed fibers.
Highlights
Nanoparticles are of great interest as a new functional material but at the same time the adverse health effect is of great concern because of their high reactivity and large surface area
The present work studied the influence of filter inhomogeneity on the collection efficiency of nanoparticles by using wire screens as uniform structure in comparison to real filters
The single fiber collection efficiencies of nanoparticles through wire screens are in good agreement with those predicted by Kirsch and Fuchs, but the dependence of real filters on Pe is somewhat smaller than –2/3 and in agreement with
Summary
Pe, in single fiber collection efficiency is not –2/3 but somewhat smaller than –2/3. Podgorski (2009) and Guillaume et al (2009) observed smaller dependence on Pe, and claimed that the fiber size distribution and pinholes are the cause of smaller dependence on Pe. The test particles are NaCl particles, which are generated by evaporation/condensation type aerosol generator. The test particles are charged in charge equilibrium state as they pass through an 241Am bipolar charger and classified into 10 nm to 50 nm by nano-DMA (Laboratory made). The DMA-classified particles are again passed through an 241Am neutralizer and charged particles are removed with a parallel-plate condenser to obtain neutral monodisperse nanoparticles. In the measurement of collection efficiency of nanoparticles, the particle loss due to diffusional deposition in conduits is of big concern. Two identical filter holders are used and they are connected in parallel so as to give the same particles loss in the conduits. With the present experimental setup, the correction for particle deposition loss is as much as 10%.
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