Researchers have discovered a new way to significantly reduce frost formation on any surface. The finding could help decrease the amount of energy needed for defrosting and could potentially result in fewer canceled flights, which can be grounded by even the slightest layer of frost.
By tweaking the texture of any material’s surface, the team was able to experimentally reduce frost formation by up to 60%. The millimeter-scale surface structure contains an optimized, jagged series of peaks and valleys, which the researchers observed in nature. With this structure, the team also showed theoretically that frost formation could be reduced by up to 80%.
The idea came from looking at leaves. There is more frost formation on the convex regions of a leaf. On the concave regions (the veins), there is much less frost. It is the geometry — not the material — that controls this. Frost forms when humid air vapor or condensation make contact with a surface that is at below-freezing temperature. Frost on airplane wings can create drag, making flight dangerous or even impossible. And when accumulating inside freezers and refrigerators, frost greatly reduces energy efficiency in appliances.
But for objects, such as leaves, that have rippling geometry, frost forms on the peaks but rarely in the valleys. The team found that condensation is enhanced on the peaks and suppressed in the valleys of wavy surfaces. The small amount of condensed water in the valleys then evaporates, resulting in a frost-free area. Even when the team used a surface material that attracts water, the water still evaporated from the valleys when below the freezing point.
This information was used to find the optimal surface texture to prevent frost formation. The best surface contains millimeter-tall peaks and valleys with small (40- to 60-degree) angles in between.
Although a thin line of frost still forms on the peaks of the surface topography, it can be defrosted with considerably less energy. It also bypasses the need for using liquids with lower frosting points or surface coatings, which can be easily scratched.