Fog collection with hairy wires

Fog collection can be an affordable, practical solution to water scarcity in many regions around the world. Commercial fog harvesters typically use mesh structures composed of cylindrical wires or thin strips. The choice of their length scale, especially the width, has been a challenge due to a trade-off problem—wide wires or strips cause fog droplets to avoid contact and display lower deposition efficiency, while meshes comprising thin cylinders or strips often suffer from clogging and exhibit low drainage efficiency. In this study, we propose a cost-effective dual-scale structure, a vertical core composed of two twisted cylindrical wires surrounded by thin hairs protruding along radial direction, which can greatly improve the water collection efficiency by decoupling the mechanisms for droplet deposition and drain: while thin hairs allow fog droplets to retain high Stokes number and deposit with high efficiency, a vertical core functions as a wicking mechanism for deposited droplets to drain quickly. Fabricated hairy wires have a water collection rate of more than two and a half times that of smooth cylindrical wires of the same diameter, and their steady-state performance does not suffer from clogging, in contrast to conventional meshes composed of thin wires. Proposed hairy wires can be mass-produced by slightly modifying commercial products. This study provides a practical solution for the optimal design of fog collectors, benefiting the fight against the global water crisis.