Collision of a Liquid Drop with a Static Hemispherical Droplet on Spherical Solid Surfaces

Experimental observations during a liquid drop impinging onto a static hemispherical droplet on steel spheres are performed using a high speed digital camera at 10,000 frames per second. The sphere diameters range from 4 mm to 16 mm. The 30 vol.% glycerol/water solution and water are selected as the experimental fluids. By increasing the impact velocity, the experimental observations present outcomes of rebound, coalescence, and circular liquid sheet successively. It is found that when the incoming droplet and the target droplet are off-centered, the circular liquid sheet has such an inclination with the horizontal line. Then the circular liquid sheet diameter is mainly discussed quantitatively, which can be increased by increasing the impact velocity or by reducing viscosity. With the increasing of the solid sphere diameter, the liquid sheet diameter varies less at the initial stage, but after the maximum value, the larger sphere diameter will lead to the larger liquid sheet diameter. A comparison of the collision behavior with different sizes of the target droplets is also performed and experimental results reveal that shapes of the liquid sheet are very different with each other, while the liquid sheet diameter almost dose not change until the maximum value, after which with the increasing of the target droplet diameter, the liquid sheet diameter can be increased slightly.