In “Star Wars”, Luke Skywalker grows up on the hot desert planet Tatooine. His family owns a moisture farm that uses devices called “vaporators” to extract drinking water from the air.
But while vaporizers are the stuff of science fiction, the technology that powers them may be closer to reality.
Researchers from Xianming “Simon” Dai’s lab at the University of Texas at Dallas are developing technology that can extract water from the air. They recently published an article in the journal Proceedings of the National Academy of Sciences featuring a more efficient way to harvest water that is inspired by a carnivorous plant.
The technology still has a long way to go before it is ready for human use. But researchers hope to one day create a wearable device that people could use to access clean drinking water in times of shortage.
“We’re trying to have water everywhere, anytime, anywhere. That’s our goal,” said Dai, an assistant professor of mechanical engineering at UTD.
Tackling water shortages
In August, 62% of Texas was facing extreme drought, according to the US Drought Monitor, a partnership between the National Drought Mitigation Center, the US Department of Agriculture and the National Oceanic and Atmospheric Administration.
Triple-digit temperatures like Dallas experienced this summer can worsen heat waves and droughts, leading to water shortages.
Dai is interested in decentralized water distribution: providing people with the water they need without using city-regulated water treatment plants and reservoirs. He has been studying water harvesting for 10 years, hoping to improve access to clean water by harnessing a natural process called condensation.
When you take a glass of cold water outside on a hot day, tiny water droplets may form on the rim of the glass. Hot water vapor in the air is drawn to the cold glass and cools, or condenses, into these droplets.
Dai and his lab aimed to harvest water using a similar approach. If they could keep a surface cool, by attracting hot water vapor to it, they could condense the water into droplets and collect it.
Nature as a source of inspiration
A problem that slows down current water-harvesting technology is that once water droplets form on a surface, they have nowhere to go.
They accumulate on the surface, slowing the formation of new droplets. Dai and his lab have developed a new solution to this problem that collects water droplets in the same way carnivorous pitcher plants devour insects.
The vase-shaped pitcher plant attracts its prey by secreting sweet nectar. When an insect lands on the upper slippery edge of the plant, it falls into the “vase”, where it is digested.
Dai and his lab set up a similar “trap” for already-formed water droplets by creating multiple T-shaped channels – smaller than a human hair in diameter – in their test water collection system. , a rectangle about 2 centimeters wide made of silicon.
As the water collects, the water droplets form at the very top of the T, which is coated with a slippery lubricant. Then the droplets slide from the T into channels where they are collected.
“If you can pull the droplet off the surface, you have more space for the condensation to reoccur,” said Dylan Boylan, a second-year Ph.D. student in Dai’s lab.
The lab’s water collection technique increased the rate of water collection compared to a model without T-shaped channels. According to Boylan, their collection surface could fill a glass of water in about seven minutes in wet conditions.
Dai’s use of canals to make water harvesting more efficient has not been thoroughly explored in existing research. There is still work to be done before its technology is available for purchase.
Dai’s water collection system relies on keeping its surface cool to draw in hot water vapor for condensation. It takes energy, especially to produce enough water to keep a family hydrated in times of shortage. The technology also relies on the presence of steam in the air to produce water, which means it could be more difficult to operate in hotter, drier climates.
Sameer Rao, an assistant professor at the University of Utah whose research interests include water harvesting and purification, said Dai’s research is an exciting advancement in the field. He added that future research will be needed to see if this technology can be scaled up to solve a problem as big as water scarcity on a national or global scale.
“It’s promising,” said Rao, who was not involved in Dai’s study. “But I think answering questions about, ‘Is it promising when you make a million? is something worth exploring.”
Now that Dai’s lab has mastered the basics of the technology, his team is scrambling to figure out how to integrate it into something scalable and affordable. Dai also sees applications for his work in systems like air conditioning, where extracting vapor from the air could help control a room’s humidity.
He said one of his favorite parts of exploring water harvesting is harnessing nature’s secrets to improve human life. Nature has been scavenging for water for quite some time: the Namib desert beetle, native to southwestern Africa, stays hydrated by condensing water droplets on its back which run into its mouth.
Dai and Boylan hope that one day humans can benefit from the process. “If we can see that nature can do it, we can take that idea and we can make it a reality for ourselves,” Boylan said.
Zongqi Guo et al, hydrophilic reentrant SLIPS enabled flow separation for rapid water collection, Proceedings of the National Academy of Sciences (2022). DOI: 10.1073/pnas.2209662119
2022 The Dallas Morning News.
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