An experimental study on melting characteristics of frozen sessile saline droplets

Icing of seawater droplets is prevalent for marine structures and substrate heating is a common de-icing method. The presence of NaCl induces distinct melting behaviors between saline and pure water droplets. This study experimentally investigates the melting characteristics of frozen sessile saline droplets with the ice profile and height, water-ice interface morphology and height, ice volume, and heat flux during the melting process acquired. The effects of initial salinity, droplet volume, and surface temperature on the above characteristics and melting stage duration are discussed. The increase of initial salinity and surface temperature and the decrease of droplet volume accelerate the droplet melting process and thus shorten the melting stage duration by 64.1 %, 61.0 %, and 53.7 % in the experimental ranges of this work. Saline droplets exhibit distinct water-ice interface morphologies compared to pure water droplets. The transient heat flux during melting is dominated by heat conduction and generally decays while the flow-induced heat convection causes an increase at the mid-term melting stage. A larger initial salinity, a smaller droplet volume, or a higher surface temperature yields a greater heat flux. Furthermore, a heat transfer model is developed by modifying the length scale to predict the melting stage durations under various conditions and achieves a prediction accuracy of ±20 %. Saline droplets exhibit distinct water-ice interface morphologies compared to pure water droplets. This research contributes to a deeper understanding of saline droplet melting and provides valuable insights for proposing and optimizing de-icing/anti-icing strategies.