Droplet Impact and Spray
The impact of a liquid droplet on a solid surface is a fascinating phenomenon. There has been much effort devoted to studies of droplet impact, motivated by the development of several technologies that involve deposition of liquid droplets on solid surfaces. Applications in which droplet impact models have been used include spray cooling of hot surfaces, ink jet printing, spray painting, fire suppression using sprinkler systems, spray forming, deposition of solder bumps on printed circuit boards, thermal spray coating, soil erosion by rain drops, and ice accumulation on electric wires and aircraft. From a researcher's viewpoint, analysis of droplet impact and splashing offers very interesting challenges. Much of the physical phenomena involved is poorly understood, including flow of free liquid surfaces, motion of a liquid-solid-air contact line, wetting of solid surfaces, and fluid instabilities that cause formation of fingers around the droplet periphery, leading to detachment of satellite droplets. The problem becomes even more complex if droplets freeze while spreading.