Water isn’t quite coming out of thin air, but it’s close.
In an effort to address global water shortages, a team at Virginia Polytechnic Institute and State University recently unveiled a new method of harvesting fresh drinking water from fog.
It’s not a new concept — fog harvesting has been a working practice since the 1980s, and several researchers, including ones at MIT, have worked extensively for years on developing the most effective methods of collecting water from mist.
But Virginia Tech professors recently presented a new design — introduced as a fog harp — to catch the water in fog, which collects three times more water than the traditional mesh netting style does, said Brook Kennedy, an industrial design professor at Virginia Tech and co-author of the study, which was published Wednesday in the journal ACS Applied Materials and Interfaces.
“With all the technology you read about — artificial intelligence, driverless cars — fog harvesting is quintessentially low-tech,” Kennedy said. “It’s remarkable effective, but not really developed considerably.”
Here’s how this water-saving practice has traditionally worked.
It started out in the mountainous regions of Chile, with screen door materials that looked like large volleyball nets, Kennedy said. It’s generally used to harvest fresh drinking or agricultural water, and it’s most effective in arid coastal regions, including the coasts of Africa, South America, Asia, the Middle East, and even California, he said.
The traps are usually comprised of mesh nettings, with vertical and horizontal wires crisscrossed together, ideally catching water droplets in the fog and letting gravity pull them into collection troughs below. In some areas, these nets collect more than 1,500 gallons of water every day, a Virginia Tech statement said.
But this isn’t a perfect system. This traditional model suffers from a dual constraint issue, said Jonathan Boreyko, a fluid mechanics professor at Virginia Tech and another co-author of the study.
If the wiring is too large, the wind passes through the net and the droplets float right through the holes without dropping into the troughs below. But if the wiring is too small, the droplets get stuck in the tiny holes, trapping it by surface tension. Once the holes are clogged, the net is impermeable to the wind, Boreyko said.
It’s a fragile balance, easily capable of tipping one way or another, so the Virginia Tech team decided to abandon the idea of crisscross mesh wiring completely.
“Our model is an array of vertical wires, which we call a harp,” Boreyko said. “It’s very efficient physically for the tiny droplets to fall down because there’s no horizontal wire obstructing the pathway.”
The team found that the harp could catch about 3 grams per centimeter squared of water per hour, as opposed to the fog net’s 1 gram, Boreyko said.
Boreyko said it’s the first time anyone has tried a harp design before, which was an idea initially inspired by nature.
“There are certain plants that essentially gather water to survive better by a process called fog drip,” Kennedy said. “Coastal redwoods in California, for example, essentially convert moving coastal fog. One-third of their water consumption comes from fog.”
There’s no cross mesh in their pine needles, he said. It’s an array of linear features.
The team’s fog harps are currently handmade, but they’re currently working to mass produce them with manufacturers that make stainless steel meshes with a wire loom, Kennedy said.
“We want to raise awareness about the preciousness of water and potential of biologically-inspired design,” he said.
Researchers estimated that two-thirds of the world’s population is suffering from “severe water scarcity” at least one month of the year, the Virginia Tech statement said.
“There’s plenty of statistics of water scarcity and billions of people who are facing water shortages,” Kennedy said. “We envision these fog harps could be deployed globally from Morocco to South Africa to Nepal to Peru to gather life-essential drinking water worldwide.”