Agrawal Amit, Bhardwaj Rajneesh
Department of Mechanical Engineering, Indian Institute of Technology Bombay, Mumbai 400076, India.
Phys Fluids (1994). 2020 Oct 1;32(10):101704. doi: 10.1063/5.0029186.
The cough of a COVID-19 infected subject contaminates a large volume of surrounding air with coronavirus due to the entrainment of surrounding air in the jet-like flow created by the cough. In the present work, we estimate this volume of the air, which may help us to design ventilation of closed spaces and, consequently, reduce the spread of the disease. Recent experiments [P. P. Simha and P. S. M. Rao, "Universal trends in human cough airflows at large distances," Phys. Fluids , 081905 (2020)] have shown that the velocity in a cough-cloud decays exponentially with distance. We analyze the data further to estimate the volume of the cough-cloud in the presence and absence of a face mask. Assuming a self-similar nature of the cough-cloud, we find that the volume entrained in the cloud varies as , where is the spread rate and is the final distance traveled by the cough-cloud. The volume of the cough-cloud without a mask is about 7 and 23 times larger than in the presence of a surgical mask and an N95 mask, respectively. We also find that the cough-cloud is present for 5 s-8 s, after which the cloud starts dissipating, irrespective of the presence or absence of a mask. Our analysis suggests that the cough-cloud finally attains the room temperature, while remaining slightly more moist than the surrounding. These findings are expected to have implications in understanding the spread of coronavirus, which is reportedly airborne.
由于咳嗽产生的喷射状气流会夹带周围空气，新冠病毒感染患者的咳嗽会使大量周围空气被冠状病毒污染。在本研究中，我们估算了这部分空气的体积，这可能有助于我们设计封闭空间的通风系统，从而减少疾病传播。最近的实验[P. P. 西姆哈和P. S. M. 拉奥，“远距离人类咳嗽气流的普遍趋势”，《物理流体》，081905(2020)]表明，咳嗽云团中的速度随距离呈指数衰减。我们进一步分析数据，以估算在佩戴和不佩戴口罩情况下咳嗽云团的体积。假设咳嗽云团具有自相似性，我们发现云团夹带的体积变化规律为 ，其中 是扩散速率， 是咳嗽云团传播的最终距离。不戴口罩时咳嗽云团的体积分别比戴外科口罩和N95口罩时大7倍和23倍左右。我们还发现，无论是否戴口罩，咳嗽云团都会持续5秒至8秒，之后云团开始消散。我们的分析表明，咳嗽云团最终会达到室温，同时比周围空气略潮湿。这些发现预计将对理解据报道通过空气传播的冠状病毒的传播产生影响。
