Department of Building Science, School of Architecture, Tsinghua University, Beijing, China.
Indoor Air. 2010 Apr;20(2):95-111. doi: 10.1111/j.1600-0668.2009.00626.x. Epub 2009 Sep 24.
This study employs a numerical model to investigate the dispersion characteristics of human exhaled droplets in ventilation rooms. The numerical model is validated by two different experiments prior to the application for the studied cases. Some typical questions on studying dispersion of human exhaled droplets indoors are reviewed and numerical study using the normalized evaporation time and normalized gravitational sedimentation time was performed to obtain the answers. It was found that modeling the transient process from a droplet to a droplet nucleus due to evaporation can be neglected when the normalized evaporation time is <0.051. When the normalized gravitational sedimentation time is <0.005, the influence of ventilation rate could be neglected. However, the influence of ventilation pattern and initial exhaled velocity on the exhaled droplets dispersion is dominant as the airflow decides the droplets dispersion significantly. Besides, the influence of temperature and relative humidity on the dispersion of droplets can be neglected for the droplet with initial diameter <200 microm; while droplet nuclei size plays an important role only for the droplets with initial diameter within the range of 10 microm-100 microm. Practical Implications Dispersion of human exhaled droplets indoor is a key issue when evaluating human exposure to infectious droplets. Results from detailed numerical studies in this study reveal how the evaporation of droplets, ventilation rate, airflow pattern, initial exhaled velocity, and particle component decide the droplet dispersion indoor. The detailed analysis of these main influencing factors on droplet dispersion in ventilation rooms may help to guide (1) the selection of numerical approach, e.g., if the transient process from a droplet to a droplet nucleus due to evaporation should be incorporated to study droplet dispersion, and (2) the selection of ventilation system to minimize the spread of pathogen-laden droplets in an indoor environment.
本研究采用数值模型研究了通风室内人体呼出飞沫的扩散特性。在应用于研究案例之前，通过两个不同的实验对数值模型进行了验证。综述了室内研究人体呼出飞沫扩散的一些典型问题，并进行了使用归一化蒸发时间和归一化重力沉降时间的数值研究，以获得答案。结果表明，当归一化蒸发时间<0.051 时，可以忽略由于蒸发而使液滴转变为液核的瞬态过程。当归一化重力沉降时间<0.005 时，可以忽略通风速率的影响。然而，通风模式和初始呼气速度对呼出飞沫的扩散影响较大，因为气流显著决定了飞沫的扩散。此外，对于初始直径<200 微米的液滴，温度和相对湿度对液滴扩散的影响可以忽略不计；而对于初始直径在 10 微米至 100 微米范围内的液滴，液核尺寸则起着重要作用。
评估人类接触传染性飞沫时，室内人体呼出飞沫的扩散是一个关键问题。本研究详细的数值研究结果揭示了液滴的蒸发、通风率、气流模式、初始呼气速度和颗粒成分如何决定室内飞沫的扩散。对这些影响飞沫在通风室内扩散的主要因素的详细分析，可能有助于指导（1）数值方法的选择，例如，是否应将由于蒸发而导致的液滴向液核转变的瞬态过程纳入到研究液滴扩散中；（2）通风系统的选择，以最大程度地减少室内环境中载病原体飞沫的传播。
