INVESTIGATION OF MOIST AIR FLOW NEAR CONTACT LINE USING MICRODROPLETS AS TRACERS

We study the trajectories of levitating microscale droplets of water in the vicinity of a contact line which is the boundary of a dry patch in a liquid layer on a heated horizontal substrate. Droplets initially form by condensation and move under the action of gravity, buoyancy, and Stokes drag force which depends on the moist air velocity. The time-dependent data on the droplet trajectories are used to obtain detailed information on the steady air velocity distributions near the contact line. An increase in the flow velocity is observed in the immediate vicinity of the contact line and explained in terms of local increase in evaporation rates. Velocity profiles are compared at different substrate temperatures.