The effects of surfactants on droplet breakup in high-speed cross flows

The breakup of droplets in high-speed cross flows is important in many industrial, naval, and environmental applications. Surfactants, which are often present in many of these applications, are chemicals that have been shown to change the behavior of free-surface fluid flows by causing surface stresses. In this talk, we investigate the role of surfactants on the aerodynamic breakup of droplets in cross flows using laboratory experiments. Droplets are generated using a needle and released into an air stream, which deforms the droplets and eventually causes them to break up into many secondary droplets. The breakup process is explored using several different concentrations of a soluble surfactant. Large-scale droplet deformations are imaged using high-speed shadowgraphy from the time the droplet is released from the needle until after it breaks up into secondary droplets. An inline holographic technique is used to measure secondary droplet statistics such as diameter (d > 50 μm), speed, ejection angle, and number. The effects of surfactants on the breakup process are reported.