Engineering Science

Water from air even in the hot sun

Unlike other radiative vapor condensers which can only operate at night, the new design works in direct sunlight and requires no energy input

May 6, 2021
The Scitech

Access to clean water is a pressing issue for many people around the world. Even in areas with ample water resources, a lack of infrastructure or reliable energy means purifying that water is sometimes extremely difficult. That’s why a water vapor condenser designed by University of Wisconsin–Madison engineers could be revolutionary. Unlike other radiative vapor condensers which can only operate at night, the new design works in direct sunlight and requires no energy input. “Water sustainability is a global issue,” says Zongfu Yu, an associate professor of electrical and computer engineering at UW–Madison. “You can’t set out to solve the water problem without addressing energy.” Yu, with University at Buffalo Professor Qiaoqiang Gan and their students, described the new radiative vapor condenser this week in the journal Proceedings of the National Academy of Sciences. In this project, the team, led by UW–Madison postdoctoral researcher Ming Zhou and supported by the National Science Foundation, constructed a small vapor condenser using a thin film of material called polydimethylsiloxane, which is very efficient at releasing thermal radiation in the atmospheric-transparency window. They layered that over silver, which reflects sunlight. The combination of the two is able to cool the condenser below the dew point, leading to condensation.

Zhou tested the device by placing it inside a condensation chamber alongside chambers containing a commercially available dew-collecting material as well as a simple “black body,” an object used for experimental comparisons because of the consistent way it absorbs and emits radiation. The team pumped humidified air into the three chambers, which they positioned on top of a UW–Madison building and, during another test, a parking garage. The polydimethylsiloxane was the only material that condensed water vapor while in direct sunlight. “Fundamentally, our radiative condenser is engineered to be in ‘thermal contact’ with the vast cold reservoir in the upper atmosphere and in outer space,” says co-author Mikhail Kats, a UW–Madison electrical and computer engineering associate professor and expert on managing infrared radiation. “The cooling power obtained via this thermal contact enables daytime water condensation with no need for an external power source.” Another benefit is that polydimethylsiloxane is widely available and relatively cheap, and the silver backing is not necessary for the condenser to work.

Source: University of Wisconsin-Madison news release