Investigation of the Impact-Freezing Process of Supercooled Droplets on Porous Surfaces

The mechanism of droplet impingement on structured porous substrates has attracted considerable attention due to its relevance in applications such as water harvesting, high-efficiency filtration, and advanced heat-transfer technologies. After impingement, a droplet spreads across the surface of the porous substrate while simultaneously undergoing imbibition into the material. The dynamic processes of spreading and imbibition involve inertia, surface tension, capillary force, and the geometrical pattern of the substrates (i.e., porosity). However, most investigations have been conducted at room temperature, and the effects of phase change, such as freezing, have rarely been considered. In our previous work, we experimentally confirmed that the freezing process of a supercooled droplet can be initiated when subjected to disturbances such as impingement. This rapid freezing process can significantly influence the dynamics of an impinging droplet on porous substrates. In this study, we experimentally investigated the impingement of supercooled droplets on substrates with different porosities and droplet-to-pore size ratios, and compared their spreading and penetration behaviors with those of droplets under non-cooled conditions. The results provide valuable references for the design and performance evaluation of porous structures in practical applications such as anti-icing materials and desalination systems.