Face mask filters—textile, surgical, or respiratory—are widely used in an effort to limit the spread of airborne viral infections. Our understanding of the droplet dynamics around a face mask filter, including the droplet containment and leakage from and passing through the cover, is incomplete. We present a fluid dynamics study of the transmission of respiratory droplets through and around a face mask filter. By employing multiphase computational fluid dynamics in a fully coupled Eulerian–Lagrangian framework, we investigate the droplet dynamics induced by a mild coughing incident and examine the fluid dynamics phenomena affecting the mask efficiency. The model takes into account turbulent dispersion forces, droplet phase-change, evaporation, and breakup in addition to the droplet–droplet and droplet–air interactions. The model mimics real events by using data, which closely resemble cough experiments. The study shows that the criteria employed for assessing the face mask performance must be modified to take into account the penetration dynamics of airborne droplet transmission, the fluid dynamics leakage around the filter, and reduction of efficiency during cough cycles. A new criterion for calculating more accurately the mask efficiency by taking into account the penetration dynamics is proposed. We show that the use of masks will reduce the airborne droplet transmission and will also protect the wearer from the droplets expelled from other subjects. However, many droplets still spread around and away from the cover, cumulatively, during cough cycles. Therefore, the use of a mask does not provide complete protection, and social distancing remains important during a pandemic. The implications of the reduced mask efficiency and respiratory droplet transmission away from the mask are even more critical for healthcare workers. The results of this study provide evidence of droplet transmission prevention by face masks, which can guide their use and further improvement.

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关于呼吸道飞沫和口罩


面罩过滤器（纺织品、外科或呼吸面罩）被广泛使用，以限制空气传播的病毒感染的传播。我们对口罩过滤器周围的液滴动态的理解，包括液滴遏制以及从盖子和穿过盖子的泄漏，是不完整的。我们对呼吸液滴通过面罩过滤器及其周围的传播进行了流体动力学研究。通过在完全耦合的欧拉-拉格朗日框架中采用多相计算流体动力学，我们研究了轻微咳嗽事件引起的液滴动力学，并检查了影响面罩效率的流体动力学现象。除了液滴-液滴和液滴-空气相互作用之外，该模型还考虑了湍流分散力、液滴相变、蒸发和破碎。该模型通过使用数据来模拟真实事件，这与咳嗽实验非常相似。研究表明，用于评估口罩性能的标准必须进行修改，以考虑到空气中液滴传播的渗透动力学、过滤器周围的流体动力学泄漏以及咳嗽周期期间效率的降低。提出了一种通过考虑穿透动力学来更准确地计算掩模效率的新标准。我们证明，使用口罩可以减少空气中飞沫的传播，也可以保护佩戴者免受其他对象排出的飞沫的侵害。然而，在咳嗽周期中，许多飞沫仍然会累积地在盖子周围和远离盖子的地方扩散。因此，使用口罩并不能提供完全的保护，在大流行期间保持社交距离仍然很重要。 对于医护人员来说，口罩效率降低和呼吸道飞沫传播远离口罩的影响更为严重。本研究结果为口罩预防飞沫传播提供了证据，可指导口罩的使用和进一步改进。