Understanding of droplet nuclei dispersion and transport characteristics can provide more engineering strategies to control transmission of airborne diseases. Droplet dispersion in a room under the conventional well-mixed and displacement ventilation is simulated. Two droplet nuclei sizes, 0.01 and 10 μm, are selected as they represent very fine and coarse droplets. The flow field is modeled using k–ε RNG model. A new Eulerian drift-flux methodology is employed to model droplet phase. Under the conventional ventilation scheme, both fine and coarse droplets are homogeneously dispersed within approximately 50 s. Droplet nuclei exhibit distinctive dispersion behavior, particularly for low airflow microenvironment. After 270 s of droplet emission, gravitational settling influences the dispersion for 10 μm droplets, and concentration gradient can still be observed for displacement ventilation.