Researchers harness evaporation to power rotary engine

A group of scientists at Columbia University have devised a way to produce energy from something that happens every time, everywhere – water evaporation. The energy is generated by a certain type of bacterial spores and while the first demonstration of the principle is quite remarkable, practical applications are still far.

Rotary engine powered by evaporation (credit: Nature Communications/Columbia University)

Rotary engine powered by evaporation (credit: Nature Communications/Columbia University)

The principle of this curious phenomenon is strikingly simple: bacterial spores known as Bacillus Subtilis expand when they absorb water and contract when they dry out. The team of researchers have thus come up with a way to glue the spores on a tape-like surface and extract the mechanical energy they produce when they expand/contract in response to changes of moisture in the air.

The study which beautifully shows the working principle in a rotary engine powered by the bacterial spores was published last Tuesday on the journal Nature Communications. “It struck me as amazing how much mechanical energy they seem to have,” says Ozgur Sahin, co-author of the study. “They are so rigid that as the material’s shape changes it produces a lot of energy.”

Sahin and collaborators glued the spores to polyimide tape and surrounded them with a shutter mechanism that regulates the passage of moisture. The shutter is in effect a mechanical switch which opens and closes in response to the force produced by the spores. When the shutter is open, moisture escapes and the spores dry out and contract, closing the shutter; when it closes, moisture fills the gap again, causing the humidity to increase and the spores to expand and repeat the cycle.

An area of eight-centimetres squared of water surface can produce about 2 µW (1 µW is a millionth of a watt) of electricity, on average. Admittedly that is not a lot, but it was enough for Sahin’s team to power an LED and a miniature car that weighs 0.1 kg. “We know actually that it can be made 100 times more powerful by solving a number of problems,” Says commented.

Some of these solutions include: adjusting the size of the moisture cavities and optimize the mechanism of the shutters. Sahin advances that arrays of the devices operating on the surface of lakes or large bodies of water could produce a new scalable and renewable energy source, but he admits that it could still be a few years before we’ll see it, if at all. It would certainly be a remarkable new way of producing clean energy as, in the end, unlike solar and wind power, evaporation is not intermittent.

A link to the video showing the spores in action can be found here.

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Carlo Bradac

Carlo Bradac

Dr Carlo Bradac is a Research Fellow at the University of Technology, Sydney (UTS). He studied physics and engineering at the Polytechnic of Milan (Italy) where he achieved his Bachelor of Science (2004) and Master of Science (2006) in Engineering for Physics and Mathematics. During his employment experience, he worked as Application Engineer and Process Automation & Control Engineer. In 2012 he completed his PhD in Physics at Macquarie University, Sydney (Australia). He worked as a Postdoctoral Research Fellow at Sydney University and Macquarie University, before moving to UTS upon receiving the Chancellor Postdoctoral Research and DECRA Fellowships.

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