Analysis of the impact dynamics of water-in-oil composite droplets on metal plates

Abstract

Composite droplets composed of immiscible liquids often have unique applications in many situations, where splashing and recoil of the composite droplet upon impact with plane surfaces are important. Due to the different properties of the constituent liquids, composite droplets will have different flow morphology than single-phase droplets. This research employs an injection method to generate composite droplets and investigates the impact dynamics of these droplets on a horizontal copper plate at room temperature using high-speed cameras. Four impact heights (H = 10 cm, 15 cm, 20 cm, 25 cm) and seven water volume fractions (α = 0.0625, 0.125, 0.1875, 0.25, 0.3125, 0.375, 0.4375) were considered. The results show that the double squeezing of the oil phase by the water phase and the copper plate is the main reason for the droplet splashing phenomenon. The degree of droplet splashing and the probability of the droplet generating a satellite droplet are directly proportional to the impact velocity. When the impact height is constant, the extent of splashing decreases with an increase in α. Additionally, the maximum value of the jetting height for composite droplets is mainly influenced by the volume of satellite droplets during the recoil process. Overall, the maximum relative jetting height of composite droplets shows an initial increasing trend followed by a decreasing trend with an increase in α. At α = 0.1875 and 0.25, there is a negative correlation between the relative jetting height and impact height. This implies that the maximum value of the relative jetting height is primarily controlled by the volume of the satellite droplets during the recoil process.