Capillary-Driven Passive Fog Harvesting With Cones From 3D Printing

Abstract Capillary pressure induced by the shape gradient of micro-cones can enable self-propelled droplet transport and promise great potential in many applications, including atmospheric water harvesting, self-cleaning surfaces, and condensation heat transfer. In order to enhance droplet mobility for fog harvesting, micro-cones are fabricated by 3D printing. Small water droplets in fog form a clamshell shape on the surface initially; then, they transition into a non-axisymmetric or axisymmetric barrel shape when growing and moving along the cone axis. In comparison with a smooth micro-cone, a rough micro-cone exhibits a reduction in water contact angle from 49o to 35o and causes different dynamics of droplet growth and transport. Preliminary results from a three-minute fog harvesting experiment show that clamshell water droplets on smooth cones remain stationary, and only half of them coalesce after growth, while barrel-shaped droplets on the rough cones fully coalesce and travel longer distances along the axis. Our analysis shows that as the droplet grows on the rough cone, it moves proportionally towards a higher cone radius, confirming the improvement of fog harvesting with rough cones.