ACS News Service Weekly PressPac: April 18, 2018

Harvesting water from fog with harps (video)

Fog Harvesting with Harps
ACS Applied Materials & Interfaces

As summertime draws near, some people around the U.S. will face annual water usage restrictions as water supplies become strained. But for those who live in arid climates year-round, water shortages are a constant concern. In these areas, residents must capitalize on even the smallest bit of moisture in the air. Now researchers report in ACS Applied Materials & Interfaces that they have developed a type of “harp” to harvest fresh water from fog.

According to the World Wildlife Foundation, as much as two-thirds of the world’s population could face water shortages by 2025. To combat this, fog harvesting is used to collect fresh water in dry climates. Current methods involve setting out a mesh netting with vertical and horizontal wires to catch water droplets, which then fall into a collector. If the wire mesh is too coarse, it cannot effectively capture water, but if the wire mesh is too fine, it gets clogged easily. Coatings and lubricants have been applied to the mesh to prevent clogging, but they don’t last and can leach into the water, contaminating it. Although previous studies have tested harp-like structures for this application, the researchers had not optimized the harps, nor had they compared their performances to mesh devices. So, Jonathan Boreyko and colleagues wanted to take those extra steps.

The researchers made three harp prototypes with uncoated vertical wires of three different diameters pulled taut on support frames. They then compared these harps with uncoated meshes that had nearly the same thicknesses. The water collection efficiency decreased for meshes with fine wires as they became clogged. But the efficiency rose with smaller-diameter wires in the harps because of a reduced pinning force of the droplets being shed along the same plane as the wires. In addition, the harps consistently collected more water than the equivalent meshes at all wire diameters. In fact, the fog harp with the finest wires collected more than three-times the amount of water of the finest mesh. The researchers also showed that the harp could be scaled up to a real-world size.

The authors acknowledge funding from the Institute for Creativity, Arts, and Technology at Virginia Tech and the Department of Biomedical Engineering and Mechanics at Virginia Tech.

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