Posted: Dec 08, 2014 |
Biomimetic dew harvesters
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(Nanowerk News) Insects are full of marvels - and this is certainly the case with a beetle from the Tenebrionind family, found in the extreme conditions of the Namib desert. Now, a team of scientists has demonstrated that such insects can collect dew on their backs - and not just fog as previously thought. This is made possible by the wax nanostructure on the surface of the beetle's elytra. These findings by José Guadarrama-Cetina, then working at ESPCI ParisTech, France - on leave from the University of Navarra, in Spain - and colleagues were recently published in EPJ E ("Dew condensation on desert beetle skin"). They bring us a step closer to harvesting dew to make drinking water from the humidity in the air. This, the team hopes, can be done by improving the water yield of man-made dew condensers that mimick the nanostructure on the beetle's back.
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It was not clear from previous studies whether water harvested by such beetles came from dew droplets, in addition to fog. Whereas fog is made of ready-made microdroplets floating in the air, dew appears following the cooling of a substrate below air temperature. This then turns the humidity of air into tiny droplets of water because more energy - as can be measured through infrared emissions - is sent to the atmosphere than received by it. The cooling capability is ideal, they demonstrated, because the insect's back demonstrates near-perfect infrared emissivity.
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Guadarrama-Cetina and colleagues also performed an image analysis of dew drops forming on the insect's back on the surface of the elytra, which appears as a series of bumps and valleys. Dew primarily forms in the valleys endowed with a hexagonal microstructure, they found, unlike the smooth surface of the bumps. This explains how drops can slide to the insect's mouth when they reach a critical size.
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