Health effect investigation by respiratory droplet residuals under different distribution methods

In enclosed environment, the respiratory droplets exhaled by contagious person always bring some virus together into the occupied spaces, which will cause negative effects on the well-being of other healthy people, and also can be related to the outbreak of the severe acute respiratory syndrome (SARS) several years ago and swine flue recently. In this paper, numerical methods are used to simulate the droplets distribution and deposition in an indoor environment with a size range from 1 μm to 10 μm under normal respiratory process. The Brownian diffusion, gravitational settling and deposition mechanism of particles are accounted by using an Eulerian modeling approach with one-way coupling. In a small office assumed, two persons are working face to face, and one of them is treated as infector, while the other is receiver. Our study aims to investigate the spatial concentration distribution and the deposition rate of the droplets exhaled by the infected people, and the exposure risk of other occupants under three typical air distribution methods, specifically mixing ventilation (MV), under-floor air distribution (UFAD), and displacement ventilation (DV). The results show that the droplets are uniformly distributed under MV, while stratified under UFAD and DV with higher concentration in the head level. Although the average concentration in the head level under DV is highest for all particles studied, the exposed concentration is lowest under DV and highest under MV for the healthy staff. As to particle deposition rate, more particles deposit on the indoor surfaces under MV, compared with UFAD and DV, with the varying particle sizes. While DV can achieve the lowest deposition rate for particles smaller than 5 μm and slightly higher deposition rate for 10 μm particles. It shows that there are highest exposure risk under MV and lowest under DV for normal respiratory process. When contagious person coughs, the exposed concentration of aerosols and inhaled dose in the simulation process is highest under UFAD and lowest under DV, which implies highest infection risk under UFAD.