Experimental and numerical investigations on the spreading dynamics of impinging liquid droplets on diverse wettable surfaces

Abstract

The impact of liquid droplets on solid surfaces is a complex multiphase flow abounding with numerous applications, particularly in heat and mass transfer fields. Though this research topic has been extensively investigated for more than two centuries, the underlying dynamics has not been completely recovered. In this work, we combine experimental observations and numerical simulations to perform a systematic study on the spreading of diverse viscous droplets on different wettable surfaces, ranging from hydrophilic to superhydrophobic. Experimentally, we spell out the coupling effect of liquid viscosity, surface wettability and impact velocity on droplet configuration evolutions, droplet-surface contact line dynamics, and dynamic variations of contact angles. Numerically, we not only reproduce the spreading characteristics of diverse impinging droplets, but also recover their energy budgets, which further allow us to understand the failure of the general theoretical model based on the energy conservation law to predict the maximum spreading factor in the experiments. We also performed analyses of the residual flow fields in the impinging droplets at the maximum spreading, where circular flows can be formed when the impact velocity is sufficiently high, and we experimentally visualized such flows.