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The impact of indoor thermal stratification on the dispersion of human speech droplets

Liu, F., Qian, H., Luo, Z. and Zheng, X. (2021) The impact of indoor thermal stratification on the dispersion of human speech droplets. Indoor Air, 31 (2). pp. 369-382. ISSN 1600-0668

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To link to this item DOI: 10.1111/ina.12737


Exhaled jets from an infected person are found to be locked at a certain height when thermal stratification exists in rooms, causing a potential high risk of disease transmission. This work is focused on the theoretical analysis of the dynamic characteristics of human speech droplets and the residual droplet nuclei in both thermally-uniform and stratified environments. Results show that most droplets generated from human speaking can totally evaporate or deposit to the ground within 1.5-2m. For small droplets of <80μm, thermal stratification shows a more significant impact on their residues. The lock-up height of the droplet nuclei is a function of droplet size and the temperature gradient, and within this lock-up layer these droplet nuclei can travel a long distance, much more than 2m. For medium droplets of 80-180μm, thermal stratification can weaken the evaporation and accelerate the deposition processes, equivalent to a higher relative humidity (RH). Accordingly, more droplets can deposit to the ground, reducing the exposure to large droplets in close proximity to the source. Large droplets of >180μm show no dependence on stratification and RH. These findings can have implications for developing effective engineering methods to limit the spread of infectious disease.

Item Type:Article
Divisions:Interdisciplinary Research Centres (IDRCs) > Walker Institute
Science > School of the Built Environment > Urban Living group
Science > School of the Built Environment > Energy and Environmental Engineering group
ID Code:92001


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