By Richard A. Lovett
Scientists are studying desert beetles looking for clues to create better ways for people in dry climates to harvest moisture from fog.
That might seem like an oxymoron, but many deserts lie in coastal areas prone to fog, says Fan Kiat Chan, a mechanical engineering graduate student at the University of Illinois, US.
Examples include Morocco, Peru, Chile, southern and east Africa and Yemen.
In some of these places, fog harvesting is already in use as a low-cost way of obtaining fresh water. That water has the advantage, Chan says, of being clean, inexpensive, and constantly replenishable whenever the fog blows in.
The technology of harvesting it, however, is still in its infancy. Much is based on fog meshes, which like the needles and leaves of trees in a cloud forest, comb water droplets out of the fog as it drifts through.
Under ideal conditions, Chan says, it’s currently possible for a 40-square-metre installation to collect 200 litres a day. That’s enough that an array of such meshes might supply household needs and irrigation water for a small village.
To date, Chan says, most of the research has focused on choosing materials that allow water droplets to easily drain into gutters and collection tanks, rather than clinging to the collector and impeding its operation.
But that’s only half the equation. Also important is designing the collector so the largest possible fraction of fog droplets are trapped by it, rather than slipping by, uncollected.
That’s where the beetles come into the picture.
Namib desert beetles (Stenocara gracilipes) survive in one of the most arid regions on Earth by turning their backs to the breeze and using their wings to collect water droplets from fog.
But their wings aren’t smooth, like those of normal beetles; they are bumpy and lined with grooves.
Curious about how this process works, Chan’s team created an assortment of grooved and bumpy surfaces and blew fog past them in a wind tunnel, looking at the way fog droplets either flowed by or collided and were collected.
Not surprisingly, he told the annual meeting of the American Physical Society’s Division of Fluid Dynamics, the beetles appear to have discovered the trick.
After trying surfaces ranging from smooth to dimpled, grooved, and bumpy, he concluded that bumps worked best – though his team still needs to “play around with this” to determine the ideal texture.
The goal, he adds, isn’t to suddenly find ways for large coastal populations to develop a new source of water – something that would require very large fog collectors and might interfere with downwind ecosystems dependent on fog-related moisture.
“The things we’re looking at are small scale,” he says.
For example, if sufficiently efficient fog collectors can be made, they could be used for portable devices, such as camping equipment. “You could use it on a water bottle that collects water [from fog],” he says.
On a slightly larger scale, it might also be possible to create fog-collecting tents for use in refugee camps, where clean water can be hard to come by.
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December 01, 2019 at 08:04PM
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