Material Breaks Record For Turning Heat Into Electricity 102
ananyo writes "A new material has broken the record for converting heat into electricity. The material had a conversion efficiency of about 15% — double that of one of the most well-known thermoelectrics: lead telluride (abstract). For decades, physicists have toyed with ways to convert heat into electricity directly. Materials known as thermoelectrics use temperature differences to drive electrons from one end to another. The displaced electrons create a voltage that can in turn be used to power other things, much like a battery. Such materials have found niche applications: the Curiosity rover trundling about on the surface of Mars, for example, uses thermoelectrics to turn heat from its plutonium power source into electricity. That doesn't mean that the material is ready to be used on the next Mars rover, however: NASA has been looking at similar materials for future space missions, but the agency is not yet convinced that they are ready for primetime."
Re:heatsinks (Score:5, Informative)
In a heat-sink you want to carry heat away from an object. A termoelectric is by definition a poor heat-sink because it requires a temperature gradient to work. This gradient means that the material is a poor conductor of heat. If it were a good conductor then both sides would quickly reach the same temperature and it would stop working.
Re:heatsinks (Score:5, Informative)
You seem to have a very poor grasp pf thermodynamics but to put it simple I will refer to the article itself.
"Building a better thermoelectric depends on finding materials that conduct electricity, but not heat"
There it is in plain language. Thermoelectrics are poor conductors of heat.
Also, nearly everything you say in your post is simply wrong. You do not convert heat into electricity. You use a heat gradient to cause an electric field. The electrons flow out one side and return to the other. You are not "piping" heat anywhere.
Thermo-electrics do not run on the heat gradient between themselves and the air. They run on the heat gradient between two sides of the material itself. I can have a block of ceramic at relatively uniform 1000C without it being 'maximally cool'.
Efficiency in sensible units (Score:5, Informative)
Considering a thermoelectric device with a cold-side temperature of 350K and a hot-side temperature of 950K, respective waste-heat conversion efficiencies of ~16.5% and ~20% are predicted.
For a hot-side temperature of 950 K and a cold-side temperature of 350 K, the Carnot efficiency [wikipedia.org] (i.e. the maximum possible efficiency of any device) is ~63%. So this is somewhere between 1/4 and 1/3 as efficient as it could possibly be. Large generators, such as combined cycle gas turbines [wikipedia.org] are considerably more efficient, but these devices are small and silent. In other words: not bad.
Re:Plutonium Power Source?! Sweet (Score:4, Informative)
Discovery in fact uses a radioisotope thermal generator (RTG) with plutonium as the power source. It used a substantial fraction of the Pu-238 available for space missions.
sPh
Re:heatsinks (Score:5, Informative)
Poor AC getting so mean comments.
Actually you ARE right, but only from a certain point of view. Firstly, you are right that thermoelectric materials take heat away, and thus cool down whatever they are attached to.
The critical point here is that merely cooling down is not enough for a heat sink. The heat sink has to be cooled down FAST. Faster than it's heat source is heating it. Thermoelectrics just can't turn heat into electricity fast enough to let a heat sink do it's job.
So it's not really a matter of thermoelectrics heating up heat sinks, they don't heat them up, they in fact cool them down, what is heating up the heat sink is the heat source (say a CPU or a power engine).
The problem is that no thermoelectric so far can transform heat intro electricity faster than a CPU turns electricity into heat.
Re:heatsinks (Score:5, Informative)
Interesting idea, but a similar thing has been done for a century+ with the outgoing steam being used to preheat the incoming water. There's orders of magnitude of difference in energy gained between that and thermocouples at huge scales. However at small scales a steam plant is not possilbe while a thermocouple is.