Force analysis of droplet motion under shear flow

The force balance at the point of motion of a shear-driven droplet on surface is studied experimentally. The experiment is carried out in a wind tunnel. A series of liquids and solid surfaces are used to obtain various contact angles of droplet. The velocity required to initiate droplet motion is measured and analyzed, and a model is formulated that describes surface tension forces at the contact line and the drag force due to the air motion, which reveals the force balance of droplet at the point of initiation. The model is good for liquid 1 motion and also offers reasonable predictions of velocity to move droplet of other liquids.