Gradient droplet distribution promotes spontaneous formation of frost-free zone

Abstract

The inhibition of condensation frosting at harsh environments is critical in various anti-icing applications. However, frosting on the entire surface is the final fate for most passive anti-icing strategies as a result of inevitable ice nucleation of subcooled droplets from the surface edges or defects and the following inter-droplet freezing wave propagation. Here, we report the frost-free zone formation on a macro-ridged surface. We design a macroscale ridge on the surface and show that this surface configuration changes the spatial distribution of water vapor diffusion flux during the condensation stage, resulting in a gradient arrangement of condensate droplets according to their size. This allows numerous failures of local inter-droplet ice bridging in the area with a critical droplet coverage rate, which triggers the interruption of the global freezing wave propagation and the evaporation of the rest droplets to form a frost-free zone around the ridge corner. These findings extend our understanding of frost formation on the surface and provide a rationale for the surface design with impressive durable anti-frosting performance.