Micro waterflows make power
Technology Research News
Energy systems are all about converting
relatively abundant forms of stored energy to forms of energy that produce
Energy can be stored mechanically, in the pressure of water behind
a dam, chemically, in the bonds that link atoms to form molecules, and
atomically, in the forces that hold together the particles that make up
The trick to tapping into the stores is coaxing energy into a
form -- like a flow of electrons -- that can be easily directed to perform
work, and to do so efficiently and without creating toxic waste.
Researchers from the University of Alberta in Canada have made
a device that taps the same principles of charge separation used by fuel
cells in order to directly convert water pressure to electricity.
The device contains millions of microscopic channels, and gleans
a small amount of electricity from the interaction between flowing water
and the surface of each channel. The researchers' prototype tapped the
water pressure generated by a hand-operated syringe to power a light-emitting
In principle, the method could be used to convert any type of
water pressure, including river flows and tides, to electricity.
For several years now, microfluidics researchers developing devices
like biochips have used electricity to move tiny amounts of fluids. As
with many things in nature, the opposite is also true. Water pressure
can produce a voltage.
Microfluidics researchers have tended to concentrate on manipulating
fluids rather than generating power, however. "I have been working on
electrokinetic phenomena for years, but not power generation," said Daniel
Kwok, a professor of mechanical engineering at the University of Alberta.
The idea of using microfluidics to generate power came as a surprise
when talking to a colleague about separating charges by pushing water
into extremely small channels, said Kwok. The two realized that if they
were able to separate charges they should be able to make an energy conversion
device, said Kwok.
The conversion process depends on the way ions naturally congregate
at the boundary between water and the glass channel. The chemical reaction
at the boundary between water and most solids leaves the solid surface
negatively charged, which in turn attracts positive hydrogen ions contained
in the water.
Ions form when atoms gain or lose an electron and so have more
or fewer negatively-charged electrons hovering over the atomic nucleus
than positively-charged protons contained in the nucleus.
This charged liquid-solid interface, known as the electrical double
layer, is a focus of research aimed at using electricity to manipulate
liquids. Applying a voltage to a water-filled microscopic glass tube causes
the positively charged ions to flow, and friction drags the rest of the
Conversely, when water is forced through a microchannel it produces
a streaming electric current by pushing the positively-charged ions in
the direction of the water current.
The researchers realized that if they put many parallel microchannels
together, creating a large surface-area-to-volume ratio, the streaming
current could add up to a potentially useful force. The larger the ratio,
the more movable ions are available, and the larger the streaming current.
The researchers tested the idea using a glass filter that contained
millions of microscopic channels. They produced electrical currents of
1 to 2 millionths of an amp by flowing water through the filter from a
30-centimeter hydrostatic pressure drop. The researchers were able to
increase the electrical flow by increasing the salt concentration in the
The device produced enough electricity to power a light-emitting
diode, according to Kwok. "So far, by a simple push on a syringe using
my hand... we can light up LEDs," he said. The hand pressure on the syringe
was about three pounds per square inch, he said.
It should be possible to scale the method up to produce larger
amounts of electricity, said Kwok. "In principle, one can scale up the
channel to do [more] work -- that should not be a problem." The method
should also work with naturally porous materials, he said.
Research into better understanding interactions at small scales
is needed before practical devices can be made, said Kwok.
Using microchannels to create streaming current drag and harnessing
energy from it is an interesting idea, said Bor Yann Liaw, an associate
specialist at the Hawaii Natural Energy Institute. "I think the idea will
work in principle; the question is how to make it work efficiently," said
It will take at least 8 to 10 years for electrokinetic microchannel
power generators to become practical, according to Kwok.
Kwok's research colleagues were Jun Yang, Fuzhi Lu and Larry W.
Kostiuk. The work appeared in the November, 2003 issue of the Journal
of Micromechanics and Microengineering. The research was funded by
the Alberta Ingenuity Establishment Fund, the Canada Research Chair Program,
the Canada Foundation for Innovation, and the Natural Sciences and Engineering
Research Council of Canada.
Timeline: 8-10 years
TRN Categories: Energy; Microfluidics and BioMEMS
Story Type: News
Related Elements: Technical paper, "Electrokinetic Microchannel
Battery by Means of Electrokinetic Microfluidic Phenomena," Journal of
Micromechanics and Microengineering, November, 2003
November 5/12, 2003
Crystal bends light backwards
Micro waterflows make
Web game reveals market
Crystal fiber goes distance
Stored data continues
Textbook queries video
Rig fires more photon
Research News Roundup
Research Watch blog
View from the High Ground Q&A
How It Works
News | Blog
Buy an ad link