Spread and recoiling of liquid droplets impacting solid surfaces

The impact of water droplets on solid surfaces is studied experimentally and theoretically. Theoretical equations based on energy conservation are developed. In our theoretical study, the droplet is modeled as a ring-like shape, which matches the dynamic shape of droplets observed from our experimental tests. In the analysis of energy conservation, the nonuniform distribution of pressure inside the deformed droplet is taken into account by introducing a flow potential energy term in the theoretical equations. To derive viscous dissipation for recoiling, a viscous layer coefficient is introduced. Its values for the tests using smooth surfaces are found to be within a small range. Both theoretical predictions and experimental data show significant influence of surface wettability on maximum spread and recoiling process. With the increase of advancing contact angle, surface energy shows a decreasing trend, whereas flow potential energy shows an increasing trend and becomes significant for hydrophobic surfaces. (c) 2014 American Institute of Chemical Engineers AIChE J, 60: 2683-2691, 2014