Freezing of impact water droplets on cold surfaces

Abstract

In addition to the operating strategies to reduce or eliminate serious damages of ice to the industrial components, it is also important to understand the fundamental freezing characteristics of the sessile and impact water droplets on the surfaces of these components. In this study, the spreading and freezing characteristics of the impact water droplet onto stationary and moving cold surfaces are investigated experimentally and numerically. Novel freezing characteristics of the deposited water droplet are observed, such as no recalescence stage, unnoticeable influence of surface wettability. In addition, scaling analyses are presented to describe the temporal evolution of the freezing front and the relationship between freezing time and surface temperature. Then, based on the experimental results of water droplets impacting on horizontal moving surfaces, two models are proposed to characterize the maximum spreading factor ratio quantificationally on different surfaces. And the contact time reduction is explained by a scaling analysis. After that, limited influence of the cold moving superhydrophobic surface on the droplet rebound behaviors is observed for the total rebound cases. A model is proposed to characterize the cooling time of the droplet to predict the threshold of the rebound behaviors. The ratio of the rebound energy to the initial energy of the droplet is found to be smaller than 0.2 for the partial rebound cases. At last, numerical models are adopted to study the freezing morphologies which changes from central-pointy to central-concave pattern under different conditions.