高效纤维滤料过滤纳米颗粒物时的反弹效应

经典过滤理论未考虑纳米颗粒物在纤维表面反弹并降低过滤效率的可能性. 选择不同等级的HEPA(高效空气过滤)玻璃纤维滤料,使用SMPS(扫描电迁移率粒度分析仪)测量粒径在10~500 nm内3种颗粒物——直角立方体MgO、圆角立方体NaCl和球形PSL(聚苯乙烯)固体颗粒的过滤效率,通过比较不同滤料状态下过滤效率的差别分析反弹效应的影响. 结果表明:①硅油熏蒸法制备的湿态滤料可以模拟过滤的理想状态. ②过滤时颗粒物反弹效应大小与其自然运动规律有关,NaCl颗粒的反弹率约为MgO颗粒的66.7%,PSL颗粒的反弹率比非球形颗粒小一个数量级左右. ③颗粒物反弹率也受到滤速的影响,在1.0~5.3 cm/s滤速范围内,反弹率与滤速成正比；滤速在5.3 cm/s时颗粒物的最大反弹率在0.363%~2.667%之间,不同颗粒物的最大反弹率不同,但最大反弹粒径相差不大. ④可以将干态滤料在5.3 cm/s滤速下对MgO颗粒的过滤作为HEPA滤料反弹效应试验的计算基准,根据形状参数(S)和过滤介质透过率的动力学模型对其他滤速和形状的颗粒物反弹率进行修定. ⑤反弹效应对透过率的影响较大,在MPPS(最易透过粒径)附近,非球形颗粒反弹效应对实际透过率的贡献可达30%~40%. 研究表明,HEPA过滤需要考虑颗粒物反弹效应对过滤效率的影响. 

Experimental Research on the Bounce Effect of Nanoparticles during Filtration by HEPA Filter Media

Classical filtration theory ignores the possibility that particles could bounce off, be re-entrained on the fiber and reduce filtration efficiency. We selected HEPA fibrous filter media of three types of efficiency in this study, and the filtration efficiencies for particles (cubic MgO particles, cubic NaCl particles with rounded edges and spherical PSL (polystyrene latex) particles) with 10 to 500 nm sizes were measured by scanning mobility particle sizers (SMPS). The impact of the bounce effect was determined by comparing the efficiency with different filter states. The results showed that a wet filter fumigated with silicone oil could be used to simulate the ideal state. There was a bounce effect of particulate matter during filtration, in which the physical laws of motion affected the bounce effect of particles with different shapes. The bounce rate of NaCl particles was 66.7% that of MgO particles, while the bounce rate of PSL particles was lower by an order of magnitude versus the unspherical ones. The bounce effect was proportional to the filtration rates in the range of 1.0-5.3 cm/s, while the maximum bounce rates ranged between 0.363%-2.667% at 5.3 cm/s. Although the maximum bounce rates of different particles were different, the particle size at the maximum bounce rate was almost the same. The bounce rate of MgO particles with a rate of 5.3 cm/s through the dry filter could be used as the basis of calculation in the bounce effect experiments. The particles with other shapes and rates could be revised according to the shape parameter S and the dynamic model of penetration. The bounce effect has a large influence on the penetration rate, because it has a contribution of 30%-40% of the penetration at the particle size near the most penetration particle size (MPPS). Therefore, much attention should be paid to the impacts of the bounce effect in HEPA filters.