Coughed droplet dispersion pattern in hospital ward under stratum ventilation

Abstract

This study aims to investigate the characteristics of coughed droplet dispersion in hospital wards under stratum ventilation (SV). The dynamic dispersion process of the coughed droplets and the spatial distribution of the droplets in a two-bed ward under SV are investigated, considering the initial size and evaporation of the droplets. For SV, the supply air grilles are on the wall opposite the patients with the centre height at 1.5 m above the floor, the exhaust diffusers are on the lower part of the wall near the patients, and the air change rate is 12 ACH. For comparison, displacement ventilation (DV) and mixing ventilation (MV) are also discussed. The RANS-based RNG k-ε model is applied to solve the flow field. The Lagrangian approach is applied to solve the droplet motion. The exposure risk in the ward is less under SV because (a) The horizontal airflow leads to a strong deposition at the initial dispersion stage that decreases droplet concentration. With the infector in the supine and sitting positions, 68% and 49% of the coughed droplets are deposited on indoor surfaces in 10 s, respectively. (b) The air jet directly supplied to the breathing zone dilutes local droplet concentration. Compared with DV and MV, SV has better control over the 50 μm diameter droplet because the higher airflow velocity under SV could increase the deposition of the 50 μm diameter droplet. Controlling the droplet dispersion in the initial stage is more efficient to improve the infection control performance of SV.