Dynamics of droplet impact on a rotating surface with different contact angles

The dynamic characteristics of the droplets impacting a smooth stainless-steel rotating surface with different Weber numbers (We) have been studied. Liquids with various surface tensions and static contact angles (ethanol, 50%, 25%, and 20% ethanol solutions, and water) have been investigated. The result reveals that the increase in both the rotational speed (ω) and We is accompanied by the droplet spreading enhancement and the droplet distortion time reduction. Ethanol (with the lowest static contact angle) shows higher β_max than other studied liquids. Moreover, clear spreading and receding behaviors can be noticed for water droplets impacting a rotating surface, which are contingent upon the physical characteristics of the droplet, the surface structure, and external force. However, the receding behavior is not observed for ethanol and various ethanol solutions during the impingement process. The range of 20%-25% volume concentration of ethanol solution is considered critical, where the outer rims of droplets distort quickly after the spreading stage, and the droplet receding phenomenon starts diminishing. A receding regime is absent due to several factors, such as contact angle, low surface tension, viscous dissipation, etc. The curve-fitting and constant values of empirical models of D s ( t ) D s . max and β max are re-estimated to reduce the error and fit the experimental data, as well as an empirical receding model for water ( D r ( t ) D s . max ) is estimated.