Research on pleated nanofiber filter for removing sub-micron aerosols

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Research on pleated nanofiber filter for removing sub-micron aerosols

 

Author: Xiao, Xiyu
Title: Research on pleated nanofiber filter for removing sub-micron aerosols
Degree: M.Sc.
Year: 2013
Subject: Nanofiltration.
Nanofibers.
Aerosols.
Hong Kong Polytechnic University -- Dissertations
Department: Dept. of Mechanical Engineering
Pages: xv, 78 leaves : ill. ; 30 cm.
Language: English
InnoPac Record: http://library.polyu.edu.hk/record=b2576824
URI: http://theses.lib.polyu.edu.hk/handle/200/6912
Abstract: Sub-micron particles with diameter from 50 nm to 500 nm are harmful to our respiratory system. These fine particles are difficult to remove by conventional microfiber filters. Empirically, quality factor, which is a measure of the efficiency per unit pressure drop, is normally used to compare filter performance. Nanofiber filter is effective on capturing sub-micron particles and pleated nanofiber filter is by far better than that of a flat nanofiber filter on filtration performance. Comparing to a flat filter, a pleated nanofiber filter has better filtration performance and lower pressure drop across the filter panel. In general, the pressure drop of the filter decreases at low pleat count due to reduced filtration area. On the other hand the pressure drop of the filter increases at high pleat count for the reason of increasing viscous drag on air flow in the space in the pleated channel. This work is to determine the optimal pleat count of pleated nanofiber filter under steady flow condition. To cover a wide range of field of filtration applications, both nanofiber and microfiber will be used in the study. An electrospinning machine is used to fabricate nanofibers made of nylon 6. Pleated filters of 0-2.44 pleat count cm⁻¹ are fabricated and tested. The face velocity is kept constant for all the tests at 20 cm/s. A Sub-Micrometer Aerosol Generator (SMAG) is used to generate sub-micron aerosols (sodium chloride) from 50 nm to 500 nm and the overall filtration efficiency is determined by measuring the count using the condensation particle counter of the mono-disperse particle aerosol to the pleated filter at both upstream and downstream of the filter. Pressure drop of different pleat count filters are also recorded.
The pressure drop is in accord with the pleated filter theory published in the literature. Pressure drop of pleated filter is much lower than that the flat filter. As the pleat count goes up, the pressure drop decreases first and subsequently increases again. A conclusion can be drawn based on the analysis of the test results that the optimal pleat count is about 2 pleat count cm⁻¹. As the pleat count increases, the filtration efficiency goes up accordingly. However pleated filter with 2 pleats cm⁻¹ shows the lowest pressure drop and highest quality factor. A commercial pleated filter made by HONDA reveals similar performance as with our nanofiber pleated filter in terms of the quality factor and efficiency for challenging particles 50-500 nm. However, the amount of fiber density used is 268 g/m² versus our nanofiber which is about 0.15 g/m². Thus the latter offers significant saving in fiber material. As an exploratory research, the property of double layers pleated filters and double electrospinning time pleated filters are tested as well. Based on some preliminary tests, it can be concluded that the double-layer filter increases filtration efficiency greatly however the pressure drop also increases as well. The double electrospinning time pleated filter has lower filtration efficiency than that of the double-layer filter yet the pressure drop is also much reduced, which renders the double electrospinning time pleated filters having much higher quality factor than the double layers pleated filters. Analysis of all the preliminary tests on the double-layer, double electrospinning time and double pleated count filters, seems to suggest that double pleat count filters is best with the quality factor.

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