Levitation conditions for condensing droplets over heated liquid surfaces.

We report experimental studies and develop mathematical models of levitation of microscale droplets over an evaporating liquid layer. The maximum size of droplets is estimated from the balance between gravity and Stokes force due to the action of upward Stefan flow generated by evaporation. Mathematical models of diffusion around levitating droplets allow us to determine Stefan flow velocity at the liquid layer surface. These results are then used to determine the dependence of levitation height on droplet size. Experimental data for a range of conditions are shown to collapse onto a single curve predicted from the model.