医院病房内呼出飞沫核形成与空气传播机理

Interpersonal transport of expiratory droplets and droplet nuclei in indoor environments constitutes a prerequisite for the transmission of respiratory diseases. Existing studies of inter-personal expiratory droplet exposure do not sufficiently consider evaporation of realistic droplets and the detailed impact of body microenvironment. This study aims to reveal the physical process of interpersonal airborne transport of droplets and droplet nuclei involving three length scales which is important for improving strategies of infection control. ..First, the composition of expiratory droplets would be simplified to NaCl solution containing suspended spherical particles (0.001-0.1mm). Our existing droplet two-stage evaporation mathematical model would be further developed to multi-stage evaporation model in order to more correctly predict droplet evaporation and dispersion in a turbulent buoyant puff induced by coughing and other respiratory activities in dry and humid air. . .Second, a series of experiments will be conducted to understand the characteristics of human exhalation airflows and thermal plume of a lying person simulated by a breathing thermal manikin (0.1-1m), in a full-scale test room with different ventilation systems. Further experiments employing two breathing thermal manikins will be carried out to evaluate the interpersonal transport of the expiratory droplets and droplet nuclei in a full-scale test ward. Numerical simulations of droplet dispersion considering droplet evaporation and droplet nucleus sizes will be carried out to evaluate the impacts of the parameters of droplet initial size, air humidity, distance between bodies , ventilation conditions , body posture, synchronization of exhalation etc on interpersonal exposure in hospital environments (1-10m) with two or more people.. .Finally, full-scale experiments and numerical simulations will also be carried out to investigate how transient events of realistic human walking and door motions influence the airborne transmission of droplet nuclei between different negative-pressure isolation rooms and within one six-bed isolation room (1-10m) with different ventilation systems.

呼出飞沫与飞沫核在人际间传播是呼吸道疾病传染的重要环节之一。已有文献对真实飞沫蒸发和飞沫核形成过程考虑不足，对人体微环境影响的研究不够细致。本项目从三个尺度出发探索病房内呼出飞沫人际间空气路径暴露过程，对医院疾病传染控制具有重要意义。首先将呼出飞沫(1-100微米)组分简化为含悬浮球状小颗粒的NaCl溶液, 并将现有飞沫蒸发二阶段数学模型发展为多阶段模型，以更准确预测咳嗽等呼出飞沫在干、湿空气中的蒸发和扩散。其次通过全尺度实验研究不同通风条件下单个躺卧暖体假人呼吸流和热羽流的特征 (0.1-1m)，以及两个暖体假人之间的飞沫传播；数值模拟研究病房环境中(1-10m)飞沫初始粒径、空气湿度、人体间距、通风设置、姿势、呼吸同步性等因素对两人或多人之间飞沫核暴露的影响。最后实验结合数值模拟研究不同通风条件下门的开关和人体走动对不同负压隔离病房之间以及同一六人病房中(1-10m)飞沫核传播的影响。

呼出飞沫与飞沫核在人际间传播是呼吸道疾病传染的重要环节之一。通过理论，实验和计算机模拟研究，我们发现飞沫核在湿润空气中的平衡尺寸比在干燥环境中大。呼出的飞沫在 干燥环境中可能传播地更远。空气传播在干燥空气中有更大的风险。这与 观测到的相对湿度或绝对湿度的重要性，以及某些呼吸道疾病，例如流感的季节性相符 合。在正常的鼻呼吸下，人体呼出的绝大部分 气流将会离开呼吸区而不会被人体重新吸入.咳嗽气流能够导致呼吸飞沫大范围的扩散。小尺寸飞沫能够 跟随气流传播很远的距离，而相对大尺寸的飞沫较快沉降。蒸发和湍流中的速度脉动对 增加飞沫的传播范围和传播距离都发挥了重要作用。与源病人的近距离接触中的疾病传播中，除了直接大飞沫沉降在他人 的身体表面而导致的间接接触传播，还包括大飞沫和短距离的空气传播。研究发现，如果易 感者与源病人之间相距1.5米以内，那么与由源病人产生的飞沫核的空气接触的机会将大 幅增加，即临近效应。大飞沫和短距 离空气传播的机理并不相同，并且他们各自的控制方法也不同。现有的对于飞沫的预防 措施以及稀释通风并不能有效地阻止短距离空气传播，因此需要新的手段加以控制. 此次研究表明，在移除污染物方面，屋顶排风口的设计比地面排风口设计有更好的效果 。真人走动产生的扰动促进了空气混合，并且身后的空气也随人往前流动。人体附近的 流场受人运动的影响，但房间中的浓度场很少受影响。我们还将我们的研究延伸到社区建筑空气通风控制的影响，以及飞沫沉淀等。