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3D printed generators recycle waste heat into energy

Posted: 02 Apr 2013 ?? ?Print Version ?Bookmark and Share

Keywords:Fraunhofer Institute? power stations? Thermoelectric generators? energy?

Researchers at the Fraunhofer Institute for Material and Beam Technology IWS have been working on a method that uses the potential lying dormant in large power stations. The 150m high concrete giants rarely manage to convert more than 40 per cent of the heat they produce into energy for electrical power. The rest is released into the atmosphere, unused. The researchers' idea is to use thermoelectric devices fitted inside cooling towers, where there can be very large differences between the hot steam and cooler concrete skin under some circumstances.

"Thermoelectric generators (TEG) currently have an efficiency of around eight per cent. That sounds very small. But if we succeed in producing TEG cost-effectively, on a large scale and from flexible materials we can install them extensively on the insides of the concave cooling tower wall. In this way, through the enormous amount of energy produced in the huge plants, we could generate large quantities of electricity," explained Dr. Aljoscha Roch of the Fraunhofer Institute for Material and Beam Technology IWS.


3D printing makes it possible: A demonstrator of a printed TEG wriggles flexibly around a sample component. Source: Fraunhofer IWS.

Together with his colleagues at the IWS, Roch has now taken a big step closer to this goal. The scientists have succeeded in producing TEG by means of a printing process. The miniaturized generators can not only be produced cost-effectively, on large surfaces and in a flexibly manageable manner, but an additional major advantage is that the materials used are environmentally-friendly.

"TEG are today largely produced by hand from toxic components which contain lead for example. We are now using modern 3D printing technology and harmless polymers (plastics) that are electrically conductive," said Roch.

The new printing technology functions in a similar way to an inkjet printer. The difference is that instead of a thin jet of ink, a thermoelectrically active polymer paste emerges from the cartridge and produces the around 20 to 30?m thick thermoelectric layers. "The generators have to be of a certain thickness in order to build up electrical voltage from temperature difference. Currently available 3D printing processes could be very suitable for achieving the required depth," says Roch.

But how is the electricity then "harvested" in a cooling tower from these polymer generators which are only a few micrometers in size? The hot steam activates the electrons in the generator, the negatively charged particles migrate to the cooler side and an electrical voltage is produced. Even small temperature differences such as one degree are sufficient for this effect. This could also be applied to car exhaust pipes.

Cars and cooling towers are, however, only two examples out of many. "In principle waste heat is produced through the operation of every technical installation. With TEG fitted on industrial production lines, in sewerage systems, at large computer centres or on any type of exhaust air system very large unused sources of energy could be developed," concludes Roch.

- Julien Happich
??EE Times

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