Filtration of nano-aerosol using nanofiber filter under low Peclet number and transitional flow regime
Filtration of nano-aerosol using nanofiber filter under low Peclet number and transitional flow regime
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DOI：
10.1016/j.seppur.2011.03.008
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发表时间：
2011-05-19
影响因子：
8.6
通讯作者：
Leung, Wallace Woon-Fong
中科院分区：
文献类型：
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作者：
Hung, Chi-Ho;Leung, Wallace Woon-Fong
本研究的目的是研究纳米气溶胶（50-500 nm）的过滤，使用强扩散捕获的Peclet数Pe下降到个位数，甚至低于1的过滤器。强滑移流或过渡流的影响，与空气分子的平均自由程的距离（即一阶的克努森数Kn（f））的数量级的流动域的尺寸相当，也已被研究与直径减小到100 nm以下的空气分子。此外，我们研究了由于使用非常小直径的纳米纤维的影响。纳米纤维过滤器通过在微纤维基底上静电纺丝尼龙6（N6）纳米纤维制成。由12、20和24%N6溶液电纺的纳米纤维的直径分别为94、185和220 nm（相应的Kn（f）为1.44、0.71和0.62）。先前的研究表明，Payet等人[1]根据中等滑移流假设开发的关于扩散机制引起的单纤维效率（eta（D））的常规半经验相关性与实验结果具有良好的一致性，即使Kn（f）增加到0.65（即过渡流态），Pe从40开始下降到6。在这项研究中，在大的滑移流（Kn（f）等于1.44），我们表明，Payet的相关eta（D），偏离测量时，Pe是小于10和偏差变得更糟，当Pe下降到低于1。因此，仅与中等扩散捕获有关的Payet相关性低估了纳米颗粒或超细颗粒（根据ISO标准[2]，尺寸小于100 nm）的单纤维捕获效率，这可能导致呼吸[3]和心血管[4]问题或疾病。因此，应根据新的测量结果建立改进的经验关联式，以准确评估过滤器对这些重要颗粒的过滤性能，以便在采取预防措施时选择和确定过滤器的尺寸。在研究纤维直径对捕获效率和压降的影响时，将d（f）从185 nm降低到94 nm有利于过滤50-500 nm纳米气溶胶，但不幸的是提高了压降（Δ P）。通过品质因数（QF）来判断效益-成本效应，对于具有更好性能的滤波器，品质因数（QF）应该更高。当过滤50-90 nm纳米气溶胶时，具有185-nm纳米纤维的过滤器的QF高于具有94-nm纳米纤维的过滤器，并且当过滤100-380 nm纳米气溶胶时，反之亦然。过滤效率随着纸基重（W）从0.042增加到0.333 g m（-2）而增加。然而，当W从0.042增加到0.085 g m（-2）时，QF迅速下降，并且从W = 0.085 g m（-2）向前缓慢地下降到W = 0.333 g m（-2）。因此，对于高性能过滤器，由一系列低基重的多层过滤器（每个层独立地被支撑）堆叠形成的多层过滤器比使用具有相同总基重的单层多层过滤器更有利。(C)2011 Elsevier B. V.保留所有权利。
The objective of this study is to investigate the filtration of nano-aerosols (50-500 nm) using nanofiber filter for strong diffusion capture wherein Peclet number Pe drops to single digit and even below unity. The effect of strong slip flow or transitional flow, with the dimension of the flow domain comparable in order of magnitude to the distance of mean-free-path of air molecules (i.e. Knudsen number Kn(f) of order one), has also been investigated with nanofiber diameter reducing below 100 nm. Also, we examined implications due to use of very small diameter nanofibers. Nanofiber filters are made by electrospinning Nylon 6 (N6) nanofibers on microfiber substrate. The diameter of nanofibers electrospun from 12, 20, and 24% N6 solution are 94,185, and 220 nm, respectively (corresponding Kn(f) of 1.44, 0.71, and 0.62). Previous studies showed that the conventional semi-empirical correlation as developed by Payet et al. [1] on single fiber efficiency due to diffusion mechanism (eta(D)) as developed from moderate slip flow assumption offers good agreement with experimental results even when Kn(f) increases to 0.65 (i.e. transition flow regime) over Pe starting from 40 and dropping to 6. In this study, under large slip flow (Kn(f) equals to 1.44), we show that Payet's correlation on eta(D), deviating from measurements when Pe is below 10 and the deviation gets worse when Pe drops below unity. Therefore, Payet's correlation, pertaining only to moderate diffusion capture, underpredicts the single fiber capture efficiency for nano-particle or ultrafine particle (sized below 100 nm according to ISO Standard [2]), which may lead to respiratory [3] and cardiovascular [4] problems or diseases. As such, an improved empirical correlation on eta(D), should be established based on new measurement to accurately assess the filter performance on these important particles for selection and sizing of filters in exercising preventive measures.In the study of effect of fiber diameter on capture efficiency and pressure drop, reducing d(f) from 185 to 94 nm facilitates the filtration of 50-500 nm nano-aerosol, but unfortunately elevates the pressure drop (Delta P). The benefit-to-cost effect is judged by the quality factor (QF) which should be higher for filter with better performance. The QF of a filter with 185-nm nanofibers is higher than the one with 94-nm nanofibers when filtering 50-90 nm nano-aerosol, and vice versa when filtering 100-380 nm nano-aerosol. Filtration efficiency increases when nanofiber basis weight (W) increases from 0.042 to 0.333 g m(-2). However, the QF drops rapidly when W increases from 0.042 to 0.085 g m(-2), and decreases slowly from W = 0.085 g m(-2) onwards to W = 0.333 g m(-2). As such, for a high performance filter a multilayer filter formed from stacking up of a series of low basis weight nanofiber layers, each independently supported, is more favorable over using a single-layer nanofiber filter with the same total basis weight. (C) 2011 Elsevier B.V. All rights reserved.