 An example of the Stefan flow occurs when a droplet of liquid evaporates in air.In this case, the vapor/air mixture surrounding the droplet is the flowing fluid, and liquid/vapor boundary of the droplet is the interface.As heat is absorbed by the droplet from the environment, some of the liquid evaporates into vapor at the surface of the droplet, and flows away from the droplet as it is displaced by additional vapor evaporating from the droplet.