Dispersion characteristics of human expiratory droplets and droplet nuclei in a mechanically ventilated general hospital ward

Abstract

Dispersion characteristics of polydispersed droplets with non-volatile content were studied in a general hospital ward equipped with ceiling-mixing type ventilation system. A multiphase numerical model was also employed to simulate the droplet dispersion tracks. Results show that the dispersion of the droplets or droplet nuclei was highly affected by the air flow pattern. The laterally projected supply jets enabled the small droplets or droplet nuclei (initial size 45μm) to exhibit a two-stage lateral dispersion behavior, in which rapid dispersions were found in the early 'initial dispersion' stage followed by much slower dispersions in the subsequent 'stable' stage. The exhaust air vent significantly enhanced lateral dispersion towards its direction. Dispersion rates increased with decrease in droplet size. Large droplets (initial size ≫ 87.5μm) were subjected to heavy gravitational effect and only the 'initial dispersion' stage behavior was observed.