Dispersion and settling characteristics of evaporating droplets in ventilated room

Movement and evaporation of small droplets in the room air are investigated in this paper through CFD simulations. A modified drift-flux model is presented with the droplet evaporation rate and the drift velocity expressed as simple algebra functions of droplet diameter, which is integrated in the transport equations of droplet number density and droplet bulk density. Evaporating droplets are treated as a continuum phase with one way coupling with the carrier phase, i.e. air. Our numerical simulations reveal that the distribution of the large evaporating droplets in the ventilated room air is characterized by a combination of the settling feature when droplets are first generated and released and the dispersion feature after the droplets are evaporated to be either very fine or become droplet nuclei. For droplets less than 50 μm in diameter, the dispersion feature is dominant in the test room that we simulated, while for droplets larger than 100 μm in diameter, the settling feature dominates. For evaporating droplets between these two sizes, the spatial distribution of droplets tends to be located at the lower part of the test room than that of small neutral aerosol particles. Within this size range, a lower initial position of the droplets in the room results in a higher deposition rate of the droplets on the floor.