Narayan Yagya, Chatterjee Sanghamitro, Agrawal Amit, Bhardwaj Rajneesh
Department of Mechanical Engineering, Indian Institute of Technology Bombay, Mumbai, 400076 India.
Trans Indian Natl Acad Eng. 2023;8(2):253-262. doi: 10.1007/s41403-023-00394-y. Epub 2023 Feb 23.
N95 mask has emerged as a potential measure to mitigate the airborne transmission of respiratory disease such as COVID-19. Herein, we experimentally investigated the impact and interaction of pure water droplets as surrogate to respiratory droplets with the different layers of a commercially available N95 mask to demonstrate the penetration and passage-capability of respiratory fluids through the different layers. The penetration of an impacting droplet through the mask layers was characterized by elucidating the ejection of secondary droplets from the rear-side surface of the target mask material. In addition, the passage of respiratory fluids through the mask layers was characterized by capillary imbibition of the droplet liquid through the pores, as a function of wettability of the mask material. Droplet impact at Weber numbers We = 208 and 416 has been considered in the present study; the chosen We range corresponds to that of cough droplets realized in real respiratory events. Each layer of the N95 mask is hydrophobic that prevents capillary imbibition through the pores: a sessile droplet placed over the surface exhibits classical diffusion-limited evaporation. Droplet impact experiments on N95 mask layer surfaces reveal that a single layer allows liquid penetration at We = 416; while a combination of five layers, as is the case of a commercially available N95 mask, blocks the penetration completely, consistent with the widely known effectiveness of N95 masks. Herein, we devote special attention to compare the so-obtained efficiency of N95 masks to that of a recently designed two-layer cloth mask containing an intermediate High-Efficiency Particulate Air (HEPA) filter layer (Narayan et al. in Phys Fluids 34:061703, 2022). We conclusively show that the performance of the designed cloth mask is identical to that of a commercially available N95 mask. The assessment of mask effectiveness further includes examination of breathability and comfort by means of passage of air through them. A comparative study has been presented herein for a clear demonstration of effectiveness of different masks in preventing air-borne transmission of COVID-19.
N95口罩已成为减轻诸如新冠病毒病等呼吸道疾病空气传播的一种潜在措施。在此，我们通过实验研究了作为呼吸道飞沫替代物的纯水液滴与市售N95口罩不同层之间的相互作用和影响，以证明呼吸道液体穿过不同层的渗透和通过能力。通过阐明从目标口罩材料后侧表面喷出的二次液滴，来表征撞击液滴穿过口罩层的渗透情况。此外，根据口罩材料的润湿性，通过液滴液体通过孔隙的毛细管吸液作用来表征呼吸道液体穿过口罩层的情况。本研究考虑了韦伯数We = 208和416时的液滴撞击；所选的We范围对应于实际呼吸事件中咳嗽飞沫的情况。N95口罩的每一层都是疏水的，可防止通过孔隙的毛细管吸液：放置在表面的静态液滴表现出典型的扩散限制蒸发。对N95口罩层表面的液滴撞击实验表明，单层在We = 416时允许液体渗透；而市售N95口罩那样的五层组合则完全阻止了渗透，这与N95口罩广为人知的有效性一致。在此，我们特别关注将如此获得的N95口罩效率与最近设计的包含中间高效空气微粒（HEPA）过滤层的双层布口罩（纳拉扬等人，《物理流体》34:061703，2022）的效率进行比较。我们最终表明，设计的布口罩的性能与市售N95口罩相同。口罩有效性评估还包括通过空气穿过口罩来检查透气性和舒适度。本文进行了一项比较研究，以清楚地证明不同口罩在预防新冠病毒病空气传播方面的有效性。
