Static freezing characteristics of saline droplets on flat substrates

Sea spray icing remains a critical hazard jeopardizing the maritime safety of vessels. To advance the mechanistic understanding of sea spray icing at the microscale, this study experimentally investigates the morphological evolution during static freezing of individual saline droplets on flat substrates. Utilizing a custom-built droplet freezing platform coupled with high-speed videography, this work systematically investigates the effects of droplet salinity, volume, and substrate temperature on volume expansion, height evolution, and contact angle variation during static freezing of saline droplets. The experimental measurements elucidate parametric influences on freezing characteristics. The results demonstrate: (1) Compared to pure water, saline droplet solidification requires an additional ‘salt precipitation’ stage; (2) at substrate temperatures ≤−24 °C, eutectic reactions during freezing significantly influence volume expansion; (3) salinity dominates droplet height evolution, with post-freezing height variations remaining below 5.3% when altering droplet volume or substrate temperature at fixed salinity. In addition, based on the experimental data, this paper proposed an empirical relationship between the morphological changes of saline droplets and the droplet salinity, droplet volume, and substrate temperature. Therefore, this study can not only be applied to practical engineering predictions under specified conditions but also help deepen the understanding of the microscopic mechanisms of saline droplet freezing.