Temperature differences give rise electricity

Temperature differences give rise to electricity

9:59 PM, 10th November 2011
Temperature differences give rise to electricity
HOT AND COLD WATER: Ole Martin Lovvik demonstrates thermoelectricity with one glass of cold and one glass of hot water. The new technology utilises the temperature difference and generates enough energy to operate a rapidly rotating fan.


OSLO, NORWAY: More than half of today’s energy consumption is squandered in useless waste heat, such as the heat from refrigerators and all sorts of gadgets and the heat from factories and power plants. The energy losses are even greater in cars. Automobile motors only manage to utilise 30 per cent of the energy they generate.

Scientists at the Centre for Materials Science and Nanotechnology at the University of Oslo in Norway (UiO) are now collaborating with SINTEF (the Foundation for Scientific and Industrial Research at the Norwegian Institute of Technology) to develop a new environmentally friendly technology called thermoelectricity, which can convert waste heat to electricity. The technology involves making use of temperature differences.

Thermoelectric materials are put to many uses in space flight. When a space probe travels far enough away from the sun, its solar cells cease to work. Batteries have much too short a lifetime. However, a lump of Plutonium will do the trick. With a temperature of a thousand degrees, it is hot. Outer space is cold. Thanks to the temperature difference, the space probe gets enough electricity. This is not a practical solution for cars and other earthly objects.

“We want to replace them with inexpensive and readily available substances,” said Ole Martin Lovvik, Associate Professor, Department of Physics, UiO and Senior Scientist at SINTEF.

With the current technology, it is possible to recover scarcely ten per cent of the lost energy. Together with the team of scientists led by Professor Johan Tafto, Lovvik is now searching for pollution-free, inexpensive materials that can recover fifteen per cent of all energy losses. That is an improvement of fully fifty per cent.

“I think we will manage to solve this problem with nanotechnology,” stated Lovvik.

The new technology will initially be put to use in thermoelectric generators in cars. Several major automobile manufacturers are already interested. Lovvik and his colleagues are currently discussing the situation with General Motors.

“Modern cars need a lot of electricity. By covering the exhaust system with thermoelectric plates, the heat from the exhaust system can increase the car’s efficiency by almost ten per cent at a single stroke,” said Lovvik.

In order to create thermoelectric materials, physicists have to resolve an apparent paradox. A metal conducts both electricity and heat. An insulator conducts neither electricity nor heat.

“This is not a simple combination and it may even sound like a self-contradiction. The best solution is to create small structures that reflect the heat waves at the same time as the current is not reflected,” said Lovvik.

“We have achieved this by using a completely new “mill.” The scientists will grind down semi-conductors to nano-sized grains. They will do that by cooling them down with liquid Nitrogen to minus 196 degrees. That makes the material more brittle, less sticky and easier to crush. Afterwards the grains are glued back together again and in this way the barriers are created,” explained Lovvik.

The scientists are now searching for next generation of thermoelectric materials. They have just tested cobalt arsenide mineral, skutterudite. “It was just recently discovered that skutterudite may have atoms located in small nano-cavities. These cavities act as barriers to heat dissipation,” concluded Lovvik. Also the thermal resistance must be as high as possible at the same time as the current must flow through easily.

(C) University of Oslo News




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