Department of Mechanical Engineering, Indian Institute of Technology (ISM)Department of Mechanical Engineering, Indian Institute of Technology (ISM)Department of Mechanical Engineering, Indian Institute of Technology (ISM)
The impact of palm oil methyl ester drops of various sizes on a PMMA surface at normal temperature and pressure is reported. The entire process of impact of a desired drop, falling from a given height, on the surface, was recorded using a highspeed camera. Drops of three different sizes were tested for three impact heights (4, 8, and 12 cm). Various subprocesses were observed. Upon impact, the drop spreads, followed by negligible recoil and partial rebound. The results show that, for a drop of a given size, the maximum spreading diameter increases with the increase in the impact height, which raises the kinetic energy, causing the drop to spread. At the initial phase, the inertia force dominates over the viscous and surface tension force, until the drop reaches its maximum spreading diameter. As the drop spreads, a ring was observed to form around the periphery. Upon reaching the maximum spread, the inner edge of the rim starts to recoil toward the center whereas the outer edge remains almost stationary. This results in the increase in the thickness of the rim. The larger resistance between the substrate and drop, i.e., adhesion, dominate over the available forces required for recoiling. The lower value of the surface tension and viscous force cannot recoil the drop back. The resistance increases with increase in the Weber number, because the increase in the spread diameter raises the adhesion. Hence, the rebound height decreases with increase in the impact height for a given drop.
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关键词
Drop impact;Spreading factor;Weber number;Wettability
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