Characterization of secondary droplets during thermal atomization regime

When a single drop impacts onto a very hot substrate with a high impact velocity the collision leads to a generation of a fast vertical spray of fine secondary droplets. These small drops are generated during disintegration of a thin drop lamella by a vapor, formed by the liquid vaporization. They are formed near the moving, disordered dewetting front. Finally, the remaining liquid of the drop breaks up into several larger fragments. The present study is focused on the characterization of such secondary droplets generated during drop impact in the thermal atomization regime. The drop impact has been observed and characterized using two high-speed video systems observing from the side and top. The characterization of secondary droplets has been performed using a dual-mode phase Doppler measurement system. The characteristic number, size and velocity of secondary droplets are measured for various parameters. It has been shown that the velocity of the secondary drops is scaled with the characteristic vapor velocity.