School of Atmospheric Sciences, Guangdong Province Key Laboratory for Climate Change and Natural Disaster Studies, Sun Yat-sen University, Guangzhou, PR China.
Department of Building Science, School of Architecture, Tsinghua University, Beijing, 100084, PR China.
J Hazard Mater. 2020 Oct 5;397:122609. doi: 10.1016/j.jhazmat.2020.122609. Epub 2020 Apr 12.
Droplet dispersion carrying viruses/bacteria in enclosed/crowded buses may induce transmissions of respiratory infectious diseases, but the influencing mechanisms have been rarely investigated. By conducting high-resolution CFD simulations, this paper investigates the evaporation and transport of solid-liquid mixed droplets (initial diameter 10 μm and 50 μm, solid to liquid ratio is 1:9) exhaled in a coach bus with 14 thermal manikins. Five air-conditioning supply directions and ambient relative humidity (RH = 35 % and 95 %) are considered. Results show that ventilation effectiveness, RH and initial droplet size significantly influence droplet transmissions in coach bus. 50 μm droplets tend to evaporate completely within 1.8 s and 7 s as RH = 35 % and 95 % respectively, while 0.2 s or less for 10 μm droplets. Thus 10 μm droplets diffuse farther with wider range than 50 μm droplets which tend to deposit more on surfaces. Droplet dispersion pattern differs due to various interactions of gravity, ventilation flows and the upward thermal body plume. The fractions of droplets suspended in air, deposited on wall surfaces are quantified. This study implies high RH, backward supply direction and passengers sitting at nonadjacent seats can effectively reduce infection risk of droplet transmission in buses. Besides taking masks, regular cleaning is also recommended since 85 %-100 % of droplets deposit on object surfaces.
在封闭、拥挤的公交车内，携带病毒/细菌的液滴扩散可能会引发呼吸道传染病的传播，但影响机制却很少被研究。本文通过进行高分辨率的 CFD 模拟，研究了在一辆有 14 个热人体模型的长途客车中呼出的固液混合液滴（初始直径为 10μm 和 50μm，固液比为 1:9）的蒸发和传输。考虑了五种空调送风方向和环境相对湿度（RH=35%和 95%）。结果表明，通风效率、RH 和初始液滴尺寸对长途客车中的液滴传播有显著影响。当 RH 分别为 35%和 95%时，50μm 液滴在 1.8s 和 7s 内几乎完全蒸发，而 10μm 液滴则需要 0.2s 或更短的时间。因此，10μm 液滴比 50μm 液滴扩散得更远，范围更广，而 50μm 液滴则更容易沉积在表面上。由于重力、通风流和向上的热体羽流的各种相互作用，液滴的扩散模式也有所不同。定量分析了悬浮在空气中的液滴和沉积在壁面上的液滴的分数。本研究表明，高 RH、向后的送风方向和乘客坐在不相邻的座位上，可以有效地降低公共汽车内液滴传播的感染风险。除了戴口罩外，还建议定期清洁，因为 85%-100%的液滴会沉积在物体表面上。
