Fog over mountains in Chinese park

‘Fog harp’ fine-tuning vastly increases water-harvesting potential

Image credit: Dreamstime

Researchers at Virginia Tech have developed a ‘fog harp’ capable of collecting three times more water than a conventional ‘fog net’.

Fog catching may sound like a thing of fantasy, but in arid and semi-arid areas which suffer water scarcity throughout summer, pure water is sometimes collected from fog using ‘fog nets’: large pieces of canvas or mesh. As droplets of water are caught on the vertical canvas, they trickle downwards, coalescing and falling into a trough at its base.

With an estimated two-thirds of the world’s population living with severe water scarcity for at least one month a year, fog nets have proved a valuable means of gathering this vital resource since the 1980s. However, installing huge fog nets in the countryside to collect water is impractical and previous efforts to collect water from fog on a large scale have proved unsustainable.

Now, a team of researchers at Virginia Tech have improved the design of fog nets to treble their collection capacity.

Researcher with fog harp

Virginia Tech

Image credit: Virginia Tech

Rather than using the usual sheet of canvas or mesh, the Virginia Tech team created an array of parallel wires – much like the strings of a harp – which shed droplets of water gathered from fog far more quickly and efficiently than conventional fog nets. The team dubbed this design the ‘fog harp’.

“From a design point of view, I’ve always found it somewhat magical that you can essentially use something that looks like a screen door mesh to translate fog into drinking water,” said Professor Brook Kennedy, associate professor of industrial design at Stanford. “But these parallel wire arrays are really the fog harp’s special ingredient.”

In a typical fog net mesh, if the holes in the mesh are too large, water droplets simply pass through, while if they are too small, the droplets block the mesh. The fog harp uses an array of small vertical wires with optimally sized gaps such that as much water can be collected as possible. Due to forgoing horizontal wires in their array, no clogging occurred. This harp-like design was, according to the researchers, inspired by nature.

“On average, coastal redwoods rely on fog drip for about one-third of their water intake,” said Kennedy. “These sequoia trees that live along the California coast have evolved over long periods of time to take advantage of that foggy climate. Their needles, like those of a traditional pine tree, are organised in a type of linear array. You don’t see cross meshes.”

The Virginia Tech team has already constructed a large prototype fog harp measuring approximately one metre square, which they plan to test on a nearby farm.

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