Tip disappearance of frozen low-concentration saline droplets

Salt spray icing poses a great threat to the safety of offshore platforms and the conduct of offshore operations. The icing characteristics of low-concentration saline droplets on cold surfaces are experimentally investigated with the effects of salinity, droplet volume, and surface temperature on the droplet height, freezing time, and freezing tip discussed. With the increase of salinity, the final droplet height and tip angle diminish but the freezing time prolongs. When the salinity increases from 0 to 20 g/kg, the normalized final droplet height decreases from 1.19 to 1.10, and the freezing time increases by 23.5 %. The freezing tip disappears in a salinity range of 15 ∼ 20 g/kg. The normalized final droplet height and tip angles are less influenced by the surface temperature and droplet volume while the freezing time goes up with the increases of the surface temperature and droplet volume. The tip angle is almost independent of the icing rate. A theoretical model is developed to relate the tip angle with the salinity. The tip disappearance of frozen low-concentration saline droplets is attributed to the change in the solid-to-liquid density ratio. The critical salinity for the freezing tip can be predicted by the theoretical model with a maximum deviation of 7.44 % compared to the experiment results. This study helps understand the icing mechanism of saline droplets and may provide new ideas for anti-icing design.