Tiny tubes squeeze electricity from water
13:18 20 October 03
NewScientist.com news service
An entirely new way of generating electricity has been discovered. The way it works is simple: squeeze water through fine pipelines and an electrical current flows.
If the output can be increased, says Larry Kostiuk of the University of Alberta in Edmonton, Canada, then high pressure water could one day be used to power small devices such as mobile phones and calculators.
Turbines are routinely used to convert the energy of flowing water into electricity, but these use the water's motion to drive a dynamo. The new device converts the motion of the water directly into current.
Physicists already knew about an electrical effect that makes it hard to force water through tiny channels. The surface of the channel walls become charged, either because ions from the water stick to them or because some of the material dissolves. This creates an electric field that hinders the flow of charged ions through the channel.
For example, when the channel walls are negatively charged they attract positive ions, which slows down their flow. Negative ions are pushed to the centre of the channel where they travel more quickly. This means negative charge builds up at the far end of the channel and positive at the near end, making it progressively harder to push the water through.
Different angle
This had always been regarded as a problem, but when Kostiuk, an engineer, learnt of the effect from his colleague Daniel Kwok, he saw its potential. "With my background in power I had a different way of looking at it" he told New Scientist. Wiring up the two ends of the channel, he realised, would give the excess charge an escape route and produce a current.
To test the idea, Kostiuk and his team pumped ordinary tap water through a block of glass riddled with half a million holes, each just a hundredth of a millimetre wide. When an electrode was attached to each end they measured a current of a few microamps.
To increase the current, they will need to increase the efficiency of the device. At the moment, says Kostiuk, "it's really pretty pathetic - a fraction of a percent."
But another way to extract more amps would be to increase the number of channels. In this respect, Nature might offer some useful power sources. Where water flows through a porous rock, for example, it squeezes through many tiny channels. Kostiuk suggests that buried electrodes could tap the current this produces.
Jordan MacInnes, an expert in fluid dynamics at the University of Sheffield, UK, expects the effect will be rather small: "It would take years to charge a mobile phone." Forcing the water through at higher pressure could cut this time, MacInnes told New Scientist, but this might raise other engineering problems.
Jenny Hogan
www.newscientist.com/news/print.jsp?id=ns99994291
� Copyright Reed Business Information Ltd.
University of Alberta, Mechanical Engineering: www.mece.ualberta.ca
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