Effect of Droplet-Removal Processes on Fog-Harvesting Performance on Wettability-Controlled Wire Array with Staggered Arrangement

Development of freshwater resources is vital to overcoming severe worldwide water scarcity. Fog harvesting has attracted attention as a candidate technology that can be used to obtain fresh water from a stream of foggy air without energy input. Drainage of captured droplets from fog harvesters is necessary to maintain the permeability of harp-shaped harvesters. In the present study, we investigated the effect of the droplet-removal process on the amount of water harvested using a harvester constructed by wettability-controlled wires with an alternating and staggered arrangement. Droplet transfer from hydrophobic to hydrophilic wires, located upstream and downstream of the fog flow, respectively, was observed with a fog velocity greater than 1.5 m/s. The proportion of harvesting resulting from droplet transfer exceeded 30% of the total, and it reflected more than 20% increase of the harvesting performance compared with that of a harvester with wires of the same wettability: this value varied with the adhesive property of the wires and fog velocity. Scaled-up and multilayered harvesters were developed to enhance harvesting performance. We demonstrated certain enhancements under multilayered conditions and obtained 15.99 g/30 min as the maximum harvested amount, which corresponds to 13.3% of the liquid contained in the fog stream and is enhanced by 10% compared with that without droplet transfer.