Ancient solar water purifier is upgraded

Adrienne SorensenAugust 2, 2018 1273 0

Ancient solar water purifier is upgraded

Solar experts are bringing back an ancient device that sanitizes water at record-breaking rates. A water purification technique that drapes a sheet of carbon-dipped paper in an upside-down "V." The paper's bottom edges soak up water, while the carbon coating absorbs solar energy and transforms it into heat for evaporation. The idea of using energy from the sun to evaporate and purify water is ancient. The Greek philosopher Aristotle reportedly discussed this more than 2,000 years ago. By draping black, carbon-dipped paper in a triangular shape and using it to both absorb and vaporize water, they developed a method for using sunlight to generate clean water with near-perfect efficiency. "Our technique is able to produce drinking water at a faster pace than is theoretically calculated under natural sunlight," says lead researcher Qiaoqiang Gan, PhD, associate professor of electrical engineering in the University at Buffalo School of Engineering and Applied Sciences. The system draws heat from the surrounding environment. The economical device could provide drinking water in regions where resources are scarce or where natural disasters have struck. The device could generate 10 to 20 liters of clean water daily. 

Modernizing the ancient idea 

Solar stills use the sun's heat to evaporate water, leaving salt, bacteria and dirt behind. It then cools and returns to a liquid state,being collected in a clean container. Gan’s them increased the device’s efficiency by cooling it down. A central component of their still is a sheet of carbon-dipped paper that is folded into an upside-down "V" shape, like the roof of a birdhouse. The bottom edges of the paper hang in a pool of water, soaking up the fluid like a napkin. At the same time, the carbon coating absorbs solar energy and transforms it into heat for evaporation. The paper's sloped geometry keeps it cool by weakening the intensity of the sunlight illuminating. It compensates for regular loss of solar energy that takes place during the vaporization process. Researchers evaporated the equivalent of 2.2 liters of water per hour for every square meter of area illuminated by the regular sun, higher than the theoretical upper limit of 1.68 liters. The team conducted its tests in the lab, using a solar simulator to generate light at the intensity of one regular sun. "Importantly, this is the only example I know of where the thermal efficiency of the solar evaporation process is 100 percent when you consider solar energy input. By developing a technique where the vapor is below ambient temperature, we create new research possibilities for exploring alternatives to high-temperature steam generation."

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