Condensation frosting and freezing of impact water droplets on cold surfaces

Abstract

The accretion of ice/frost stemming from condensation frosting and freezing of impact water droplets is pervasive in both nature and industry, causing enormous losses every year worldwide especially in aviation and transportation. Most existing studies regarding condensation frosting focus on the anti-frosting potential by leveraging the ice-liquid or icevapor interactions on two-dimensional structured surfaces. Little is known about condensation frosting on one-dimensional surfaces with temperature gradient. This thesis first reports on the non-uniform condensate morphologies on a cantilevered microfiber during condensation due to the competition between conductive thermal resistance within the fiber and condensation heat transfer resistance on the fiber surface. Scaling analyses were provided to reveal the underlying physics. During the frosting phase, the nucleation of supercooled liquid microdroplet is triggered at locations where ice bridges are upon contact instead dropletsubstrate interfaces. Furthermore, an inter-droplet ice wicking regime is reported where the liquid droplet is sucked by physical contact of ice bridge, different from the classical interdroplet ice bridging. Such phenomenon results from the competition between wicking dynamics and nucleation crystallization timescales. Intriguingly, the frosting morphology on the microfiber demonstrates a similar trend to the condensate morphology. Moreover, the directional migration and easy assembling of melted water can be achieved by tailoring the fiber length and cooling temperature during defrosting, and well explained by the analytical models proposed. Additionally, a unique distribution pattern of condensed droplets is found during condensation on stainless-steel mesh, with one droplet atop every other knot. Such phenomenon arises from the extent of the region of inhibited condensation imposed by the central knot within the smallest periodic unit of the distribution pattern. Lattice Boltzmann simulation is implemented to obtain the water vapor concentration, and the pattern region under