How far droplets can move in indoor environments - revisiting the Wells evaporation-falling curve
How far droplets can move in indoor environments - revisiting the Wells evaporation-falling curve
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DOI：
10.1111/j.1600-0668.2007.00469.x
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发表时间：
2007-06-01
期刊：
影响因子：
5.8
通讯作者：
Seto, W. H.
中科院分区：
文献类型：
--
作者：
Xie, X.;Li, Y.;Seto, W. H.
据信，许多传染病是通过大飞沫和空气传播的。了解液滴和液滴核的蒸发和分散不仅对制定有效的传染病工程控制方法具有重要意义，而且对探索传染病的基本传播机制具有重要意义。飞沫移动的距离与飞沫传播疾病的传播距离有关。本文建立了一个简单的物理模型，用于研究呼吸活动中喷出的液滴的蒸发和运动；特别是，考虑到相对湿度、空气速度和呼吸射流的影响，重新审视了著名的威尔斯液滴蒸发下降曲线。我们的简单模型考虑呼出空气的运动，以及单个液滴的蒸发和运动。呼出的空气被视为一种稳态的非等温（热）射流，水平地向周围停滞的空气中释放。假设液滴在非等温射流中蒸发并运动。对纯水滴和氯化钠（生理盐水）溶液滴（0.9% w/v）进行了计算。我们计算了液滴的寿命和液滴大小的变化，以及液滴在不同相对湿度下移动的距离。我们的结果表明，液滴的大小主要决定了它在被排出后的蒸发和运动。在下落之前完全蒸发的最大液滴的大小是在不同条件下确定的。得到了飞沫在不同呼吸活动中所能到达的最大水平距离。我们的研究有助于制定有效的预防措施，以控制医院和整个社区的传染病。
A large number of infectious diseases are believed to be transmitted between people via large droplets and by airborne routes. An understanding of evaporation and dispersion of droplets and droplet nuclei is not only significant for developing effective engineering control methods for infectious diseases but also for exploring the basic transmission mechanisms of the infectious diseases. How far droplets can move is related to how far droplet-borne diseases can transmit. A simple physical model is developed and used here to investigate the evaporation and movement of droplets expelled during respiratory activities; in particular, the well-known Wells evaporation-falling curve of droplets is revisited considering the effect of relative humidity, air speed, and respiratory jets. Our simple model considers the movement of exhaled air, as well as the evaporation and movement of a single droplet. Exhaled air is treated as a steady-state non-isothermal (warm) jet horizontally issuing into stagnant surrounding air. A droplet is assumed to evaporate and move in this non-isothermal jet. Calculations are performed for both pure water droplets and droplets of sodium chloride (physiological saline) solution (0.9% w/v). We calculate the droplet lifetimes and how droplet size changes, as well as how far the droplets travel in different relative humidities. Our results indicate that a droplet's size predominately dictates its evaporation and movement after being expelled. The sizes of the largest droplets that would totally evaporate before falling 2 in away are determined under different conditions. The maximum horizontal distances that droplets can reach during different respiratory activities are also obtained. Our study is useful for developing effective prevention measures for controlling infectious diseases in hospitals and in the community at large.