Scientists develop faster way of pulling water vapour out of the air

Development could have dramatic implications from survival in arid environments to commercial processes

Steve Connor
Science Editor
Wednesday 24 February 2016 19:23
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Condensation on a window. Researchers have designed a surface to capture and store water droplets
Condensation on a window. Researchers have designed a surface to capture and store water droplets

A beetle, a cactus and a fly-catching plant have each provided inspiration for scientists who have developed a way of pulling water vapour out of the air ten times faster than standards methods of condensation.

The researchers have designed a surface that uses nature’s own ways of catching water droplets and transporting them for safe storage.

They believe it is many times more effective than the most efficient water-condensation surfaces currently in commercial use.

The development could have dramatic implications for a range of applications, from survival in arid environments to commercial processes that require rapid and efficient water condensation – from power plants to greenhouses.

A desert beetle, which collects moisture on its back, a cactus, which directs water droplets down its spines towards its roots, and the slippery surface of an insectivorous pitcher plant were all used to design a surface that collects condensed water vapour and rapidly transports the liquid to a collecting area, the scientists said.

The surface is so effective it can draw water vapour from the air and even transport it against the influence of gravity or unfavourable temperature gradients, which could prove invaluable in some industrial situations, the scientists said.

“Thermal power plants, for example, rely on condensers to quickly convert steam to liquid water. This design could help to speed up that process and even allow for operation at a higher temperature, significantly improving the overall energy efficiency,” said Philseok Kim of Harvard University in Cambridge, Massachusetts.

“This research is an exciting first step towards developing a passive system that can efficiently collect water and guide it to a reservoir,” Dr Kim said.

Current approaches to pulling water vapour from the air use technology that are good at either promoting either the growth of water droplets or the “shedding” of water droplets away from the condensation area – but rarely both together.

However, the scientists exploited the physical attributes of three living organisms that have evolved to do one or both of these functions, and then combined what they learnt into a single, synthetic surface that exploits the evolved traits.

Millimetre-sized bumps on the back of the Namib desert beetle, for instance, have evolved to encourage the condensation of water into large droplets. The scientists analysed the shape and size of these bumps, along with the water repellent surface coating on the beetle’s back, to design a similar bumpy surface.

They combined this with the attributes of cactus spine which has a geometry that optimises the movement of water down a slope. Finally, they added the slippery surface of a pitcher plant, which is designed to trap flies, which has a slippery “nanocoating” that encourages the natural capillary-movement of water – which can work against gravity if necessary.

“We experimentally found that the geometry of bumps [of the beetle] along could facilitate condensation,” said Kyoo-Chul Park, a postdoctoral researcher at Harvard and lead author of the study published in Nature.

“By optimising that bump shape through detailed theoretical modelling and combining it with the asymmetry of cactus spines and the nearly friction-free coatings of pitcher plants, we were able to design a material that can collect and transport a greater volume of water in a short time compared to other surfaces,” Dr Park said.

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