Experimental and mathematically validated studies of pure water droplet freezing under natural free convection

Supercooling is a challenge in various fields, including freeze-desalination, frozen-food industry, and phase-change materials. Supercooling of brine reduces the desalination efficiency and cost. Study of freezing droplet provide understanding to supercooling and crystallization processes. Here, we present experimental measurements for water droplet freezing to investigate the role of the droplet volume, cooling temperature, and nucleating agent on the extent of the supercooling-degree. Results show that supercooling-degree increases with decreasing cooling temperature, but decreases with increasing droplet size. Adding AgI nucleating agent significantly reduced the supercooling-degree. The crystallization time is found to be inversely proportional with supercooling-degree. When cooling temperature decreases from −15 to −30 °C, the supercooling-degree increases from 13.4 to 16.7 °C and the crystallization time decreases from 84.0 to 49.6 s; When the droplet size increases from 2 to 9 μL, the supercooling-degree decreases from 15.6 to 12.4 °C and the crystallization time increases from 31.9 to 106.9 s. And when AgI concentration increases from 0 to 0.5 % in the pure water, the supercooling-degree decreases from 13.4 to 3.3 °C and the crystallization time increases from 84.0 to 121.6 s. This work highlights and captures the supercooling-degree and numerically models the entire freezing events.