We all know that the freshwater is very important for us. Freshwater environments include rivers, lakes, wetlands, streams and underground aquifers. They store and clean the water that’s crucial for people and wildlife. It’s benefits is to supply water for drinking, growing crops, manufacturing etc. They also help to prevent erosion, dispose of waste and provide natural protection from flooding. It is scarce in many parts of the world and it must be obtained at great expense.
Freshwater scarcity
Because of carelessness, freshwater environments have been mismanaged, leading to pollution, drying rivers and damaged habitats. In the last century we’ve lost so many of the world’s wetlands and their wildlife. Dams disrupt natural river flow, which can affect people downstream that rely on the river. Unsafe water has had severe health and financial costs. Rising water consumption is putting pressure on water resources: by 2030 nearly half the world’s population will live in areas of high water stress.
Current Technologies
In coastal areas, freshwater is obtained by desalination of salt water. The only remaining option is to condense atmospheric humidity through cooling, either through processes that similarly require high energy input or by using “passive” technologies that exploit the temperature swing between day and night. With current passive technologies, such as dew-collecting foils, water can be extracted only at night. This is because the sun heats the foils during the day, which makes condensation impossible.
Self-cooling and protection from radiation
ETH Zurich Researchers have developed a technology that harvests fresh water 24 hours around the clock, with no energy input, even under the blazing sun. The device consists of a specially coated glass pane, which both reflects solar radiation and also radiates away its own heat through the atmosphere to the outer space. It cools itself down to as much as 15 degrees Celsius (59 degrees Fahrenheit) below the ambient temperature. On the underside of this pane, water vapour from the air condenses into water.
The scientists coated the glass with specifically designed polymer and silver layers. This special coating causes the pane to emit infrared radiation at a specific wavelength window to the outer space, with no absorption by the atmosphere nor reflection back onto the pane. A novel cone-shaped radiation shield deflects heat radiation from the atmosphere and shields the pane from incoming solar radiation. This allows the device to radiate the aforementioned heat outward and thus to self-cool, fully passively.
Close to the theoretical optimum
The device is tested on the roof of an ETH building in Zurich. It can produce at least twice as much water per area per day as the best current passive technologies based on foils: the small pilot system with a pane diameter of 10 centimetres delivered 4.6 millilitres of water per day under real-world conditions. Under ideal conditions, the device could harvest up to 0.53 decilitres (approximately 1.8 fluid ounces) of water per square metre of pane surface per hour. Iwan Hächler, doctoral student and professor of Thermodynamics at ETH Zurich said that this is close to the theoretical maximum value of 0.6 decilitres (2.03 ounces) per hour, which is physically impossible to exceed.
In other technologies, the condensed water is wiped from the surface. The ETH Zurich researchers applied a novel super hydrophobic (extremely water-repellent) coating to the underside of the pane in their water condenser. This causes the condensed water to bead up and run or jump off on its own accord.
Future Goals
The researchers’ goal is to develop this technology in other countries. They say that the other countries can either further develop this technology or a combination of this technology with desalination of saltwater. The production of the coated panes is relatively simple and building water condensers that are larger than the current pilot system ought to be possible.
Story Source
Materials provided by ETH Zurich. Original written by Fabio Bergamin.
Journal Reference
- Haechler I, Park H, Schnoering G, Gulich T, Rohner M, Tripathy A, Milionis A, Schutzius TM, Poulikakos D. Exploiting radiative cooling for uninterrupted 24-hour water harvesting from the atmosphere. Science Advances, 23 June 2021 DOI: 10.1126/sciadv.abf3978
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