Scientists are harvesting water by building fog harps and zapping the air

>June 8, 2018

Scientists are harvesting water by building fog harps and zapping the air

Scientists are harvesting water by building fog harps and zapping the air

Scientists are harvesting water by building fog harps and zapping the airThe Earth is 70 percent water, but almost all of that liquid is seawater us humans can’t drink. Already, California is besieged by drought, while citizens in South Africa’s Cape Town try to push back Day Zero, the day the city runs out of water. As our population grows and temperatures rise, the global water crisis worsens, spurring scientists to develop better ways of harvesting water.

Around the world, people living on coasts collect water by harvesting the fog. “Fog is a cloud very low on the ground,” explains Jonathan Boreyko, an engineer at Virginia Polytechnic Institute and State University who studies nature-inspired fluids. Fog harvesters are mesh nets, usually one meter squared, erected perpendicular to the path of the wind. As the wind blows fog through the device, the mesh catches the droplets, and gravity pulls the water down into containers underneath. Most of the time, fog harvesters collect about three liters a day per square meter of mesh.

The beauty of fog harvesters, explains Boreyko, is that they take very little effort. The harvesters can be used in remote areas and don’t need constant supervision; just set it up, and collect water at the end of the day.

But they’re not very efficient, in part because the mesh holes have to be just the right size. If they’re too large, the droplets will escape through it. “But if you make them too small, the water is going to get clogged within a matter of seconds because of surface tension, and so it won’t slide down and won’t be easily collected,” Boreyko says. It’s hardly reasonable to have someone wringing the clogged mesh constantly.

So Boreyko worked with Virginia Tech industrial designer Brook Kennedy to create a more efficient harvester that they call a “fog harp.” (Their research was recently published in ACS Applied Materials and Interfaces.) Kennedy had spent time in northern California, where the giant redwoods get almost a third of their water from the rolling fog that comes in from the Pacific. “Their needles aren’t shaped like volleyball nets or screen door mesh,” says Kennedy. “They’re linear, and that was the little bit of insight that connected with what Jonathan had been working on.” Inspired by the trees, Kennedy and Boreyko’s “fog harp” only has vertical wires.

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