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Revisit of Spread-Rebound Transition Criterion in Droplet-Wall Impingement
Sung Uk Ryu and Sang Yong Lee

In the present work, spread/rebound regime and transition criterion of a single water droplet impacting an unheated dry wall has been experimentally investigated. The droplet was directed on a Teflon coated plate, and the impinging behavior was visualized and recorded using a CCD camera. Droplet diameter and velocity approaching the wall were measured as well. The rebound mode appeared at the higher Weber number and/or the Reynolds number conditions compared with the spread mode. Based on the present experimental data, the Weber number criterion between the spread and the rebound modes turned out to be higher compared to that by the Mao et al.’s result. This change is considered to be due to difference between the actual shape and the model shape of the droplet at the maximum spread. In the present work, an improved model for an impacting droplet was proposed based on a more realistic shape of the droplet at the maximum spread. The improved model represents the measured values within accuracy of ±5% with more than 90% of the experimental data from different sources.

Keywords: Rebound regime, spread regime, transition criterion, maximum spreading ratio, half-torus shape, single droplet.

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