Evaporation and dispersion of exhaled droplets in stratified environment

Exhaled droplets of an infected person can spread diseases with the expiratory flows in indoor environments. This work focuses on how the thermal stratification affects the evaporation and dispersion of exhaled droplets by using a theoretical integral model. Pure water droplets with different diameters (10-240μm) are exhaled and disperse with different RHs (0, 30%, 50% and 60%). Results show that for medium droplets (50-170μm), the thermal stratification can obviously weaken the evaporation of droplets due to less heat and mass transfer between droplets and ambient air. The droplets were similarly influenced when the ambient RH increases from 0 to 50%, particularly, the 50μm droplets showed an obvious fluctuation trend with the jet flow at the lockup height in the stratified environment. When RH increased to 60%, a possible condensation phenomenon occurred on droplets, increasing the suspending time of droplets in the air. This theoretical model will be useful to control infectious diseases in rooms, especially when the thermal stratification exists.