Turning Waste Heat into Power

Thursday, September 30, 2010 @ 08:09 AM gHale

By using a novel “pyroelectric” method, it may soon be possible to power tiny devices using waste heat.
Using tiny structures called ferroelectric nanowires, they can rapidly generate an electrical current in response to any change in the ambient temperature, harvesting otherwise wasted energy from thermal fluctuations, according to a joint team of Ukrainian and American scientists.
“The second law of thermodynamics rules modern life: Through all kinds of industry, humans consistently produce an enormous amount of waste heat,” said lead researcher Anna Morozovska of the National Academy of Sciences of Ukraine. “However, the laws of thermodynamics do not exclude rescuing some of this energy by harvesting the thermal fluctuations to produce electricity.”
Pyroelectrictricity can play key role in consumer electronics, said Morozovska, and recovering this heat in the form of pyroelectric energy may bring about a new era of “tiny energy.”
Pyroelectric nanogenerators could be extremely useful for powering specific tasks in biological applications, medicine and nanotechnology, particularly in space because they perform well in low temperatures.
In an investigation of the pyroelectric properties of ferroelectric nanowires, the team analyzed how the pyroelectric coefficient corresponds to the radius of the wire and its coupling. They found the smaller the wire radius, the more the pyroelectric coefficient diverges until a critical radius at which the response changes to paraelectric (above the Curie temperature). This “size effect” could tune the phase transition temperatures in ferroelectric nanostructures, thus enabling a system with a large, tunable, pyroelectric response.
In theory, the use of rectifying contacts could enable the polarized ferroelectric nanowire to generate a giant, pyroelectric, direct current and voltage in response to temperature fluctuations which you could harvest and detect using a bolometric detector. Such a nanoscale device would not contain any moving parts and could be suitable for long-term operation in ambient applications such as in-vitro biological systems and outer space. The researchers calculate these little nanogenerators would have very high efficiency at low temperatures, decreasing at warmer temperatures.

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