Air becomes a constant source of water

The sun scorches and dries everything – but even in desert regions there is always plenty of water – in the form of moisture. Swiss scientists now present a surprisingly uncomplicated concept that allows this treasure to be used around the clock for the first time: they have developed a particularly efficient condenser system that, thanks to self-cooling and without energy consumption, can also draw water from the humidity during the day. Since production costs are low, the system can make a useful contribution to water supply in arid regions, developers say.

Until now, fresh water could only be obtained with great effort: in coastal areas, seawater is desalinated, which requires a lot of energy. Inland, on the other hand, water can often only be obtained through condensation. Energy-intensive cooling technology is also used for this purpose – but so-called passive technologies such as dew-collecting films and absorber systems have already been developed. However, with the previous methods, water can only be extracted from moisture at night. On the other hand, in the heat, previous passive technologies do not allow condensation. Because the principle is like breathing on a glass pane: tiny water droplets are only formed because of the significant temperature difference between the air to breathe and the pane of glass.

Sophisticated passive cooling

However, scientists led by Ivan Hächler from the Swiss Federal Institute of Technology in Zurich have now developed a technology that allows them to obtain water for the first time around the clock without any energy source – under realistic humidity conditions. and even in the scorching sun. The system essentially consists of a specially coated glass pane that both reflects solar radiation and can effectively emit its own heat. As a result, it cools down surprisingly quickly: scientists report that the disk reaches temperatures as low as 15 degrees Celsius below ambient temperature. Due to such a large temperature difference, moisture condenses on the bottom – tiny droplets of water form. In fact, the process is the same as in the case of poorly insulating glass in winter.

Condenser system concept. (Photo: Haechler I et al. Science Advances 2021, ed.)

As reported by the creators, the secret of the “cool” dial is a sophisticated coating made of polymers and silver. This material causes the glass to emit infrared radiation with a specific wavelength range. The scientists explain that this frequency is not absorbed by the atmosphere and is not reflected back to the disk by the molecular components of the air. Another important element of the system is the newly developed conical radiation shield. This makes it possible to largely stop the thermal radiation from the air and the solar radiation from the pane, but at the same time allows the thermal radiation and thus cooling.

Promising dribble

Scientists report that the underside of the condensation disk also has a sophisticated coating. As they explain, with other technologies, the condensed water usually has to be wiped off the surface, which is associated with a lot of effort. Otherwise, some of the condensed water would stick to the surface and thus could not be used and would impede further condensation. In the new system, the water condenser has an extremely waterproof – super hydrophobic – coating. As a result, the condensed water drains away intensively. “Unlike other technologies, we really don’t need any extra energy, which is a decisive advantage,” says Hächler.

As demonstrated by tests in a small pilot plant under real conditions, the new technology can extract at least twice as much water per area per day as the best previous passive film technologies. Scientists’ calculations show that under ideal conditions, larger systems can extract up to 53 milliliters of water per square meter of disk area and hour. As with solar cells, multiple water condensers can be placed side by side to provide more water. Importantly, the production of coated glass is relatively straightforward, the researchers say. The system can make an interesting contribution to supply, especially in water-stressed developing and emerging countries. Hächler and his colleagues are now calling on other research teams to further develop the technology or combine it with other methods to further increase efficiency.

Source: ETH Zurich, Technical Article: Science Advances, doi: 10.1126

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