Scientists at Columbia University have made two new devices that extract energy directly from the evaporation of water.
An immensely powerful yet invisible force brings water from the earth to the top of the tallest redwood and distributes snow to the peaks of the Himalayas.
Yet despite the power of water evaporation, its potential to power self-sufficient devices or produce electricity has remained largely untapped until now.
Researchers predict that the evaporation of water could one day produce electricity from giant mobile power generators located in bays or reservoirs or from huge rotating machines similar to wind turbines that are placed above the surface, predicts the lead author of the work. , Ozgur Sahin, Associate Professor of Biological and Physical Sciences at Columbia University.
"Evaporation is a fundamental force of nature - Sahin points out -. It is everywhere and it is more powerful than other forces such as wind and waves."
Last year, Sahin found that when bacterial spores shrink and swell with the change in humidity, they can push and pull other objects with force.
These spores carry more energy, in proportion, than other materials used in engineering to move objects, according to a paper published in 'Nature Nanotechnology', which builds on work Sahin had started when he was at the Wyss Institute for Biologically Inspired Engineering in Harvard University.
Building on last year's results, Sahin and his Columbia colleagues looked at how to build real devices that could be powered by this type of energy.
To build a movable piston engine, the researchers first glued spores to both sides of a thin, double-sided plastic tape, similar to that of cassette tapes, creating a dashed line of spores.
They did the same on the opposite side of the tape, but offsetting it, so that the gaps on one side were covered with traces of spores on the other.
When the dry air contracted the spores, the spore shell curled, transforming the straight ribbon into wavy and shortening it. If one or both ends of the tape stay anchored, the tape pulls whatever is anchored.
Conversely, when the air is humid, the tape stretches, releasing the force.
The result is a new type of artificial muscle that is controlled by the change in humidity. So, Sahin and Xi Chen, a postdoctoral researcher in their lab, placed dozens of these tapes side by side, creating a stronger artificial muscle that they then put inside a floating plastic box topped with blinds.
Inside the box, the evaporated water made the air humid and the humidity caused the muscle to lengthen and the blinds to open, causing the air to dry out.
When the moisture was gone, the spores shrunk and the tapes contracted, pulling the blinds closed and allowing moisture to build up again. Thus, a self-sustaining cycle of movement was created.
"When we put water under the device, it suddenly came back to life, it moved by itself," celebrates Chen.
The spore-covered artificial muscles function like a piston powered by evaporation. By coupling the piston to a generator, it produced enough electricity to make a small light flicker.
"We convert the evaporation of a pool of water into light", sums up Sahin.
With its generation of electrical power, the evaporative motion motor could supply tiny lights or sensors on the ocean floor to monitor the floating environment, Chen suggests, speculating that an enhanced version with stickier plastic tape and more spores could potentially generate even more energy per unit area than a wind farm.
Another new evaporative-powered motor from Columbia's team - a "Moisture Mill" - contains a plastic wheel with flanges protruding from the belt coated on one side with spores.
Half of the wheel is in dry air, causing the tabs to curl, and the other half is in humid environment, where the tabs are straight.
As a result, the wheel turns continuously, effectively acting like a rotary motor. The researchers then built a small toy car, powered by this moisture-driven mill, and were successful in getting the car to roll on its own, powered solely by evaporation.
In the future, according to Sahin, it may be possible to design engines that use mechanical energy stored in spores to power a life-size vehicle. Such an engine, if achieved, would not need to burn fuel or an electric battery.
A larger version of this mill could also produce electricity, Sahin says, like a wheel that hovers over a large body of water and where salty water evaporates, causing the wheel to turn and generate electricity.
This system would constantly produce as much electricity as a wind turbine, Sahin predicts.
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