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Old 8th February 2007, 05:49 PM   #1
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Post Thermopile, let extract some electricity from heat without steam

I want to build a Thermopile to generate usable electricity with a heat source, like a small fire or something,
I can build something like this but, I only get 1 mA and an ant of a volt. And it subjected to 1700C blow torch, it sucks.

So does anyone have some info about that, would be nice, to light a candle and then your able to watch a DVD
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Old 8th February 2007, 06:15 PM   #2
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Jacques, please do some research, and read up on the laws of thermodynamics. This is, in principle, no different to any of your questions from your other threads.

Here is a good place to start.

http://en.wikipedia.org/wiki/Laws_of_thermodynamics
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Old 8th February 2007, 06:23 PM   #3
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And just so I don't seem totally negative, here is your best bet for getting energy from heat.
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Old 8th February 2007, 07:22 PM   #4
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Yip, thanks pinkmouse, Iíve already checked out Laws of thermodynamics and also have tried to build a Stirling engine, but did not work so nice, Iím looking something more into solid state device and for something with a high wattage output.
How I see it, it sucks up a lot of watts to heat up n heating element, say like 1000W heater. But if you apply 1000W heat source to some thermocouples, you will newer get that 1000W back, I belief if you can covert something to another thing, then you can surely convert it back with at least 100% back in theory, but mostly we strive near
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Old 8th February 2007, 09:42 PM   #5
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[geeky, boring scientist mode]
Thermocouple power sources are horrendoulsy inefficient- about 10%. Therefore, you cannot get 'at least 100% back'. Not possible. The thermo couple is a heat engine:

____________
| Heat Source|
_____|_______
(Heat engine)-------> |useful work|
_____|___
|Heat sink|

(I apologise at my first attempt at ASCII drawing)

The heat energy moves from the heat source through the heat engine, where it produces useful work, and then the waste energy goes to the heat sink.

In a perfect heat engine, once the useful work is produced, there are no more losses, but in practice this is not the case (E.g. friction in an Internal Combustion Engine (ICE)).

The maximum theoretical effiecency of a 'perfect heat engine' is:


1- Temperature of 'heat sink'
__ Temperature of heat source.


All temperatures for this formula must be in Kelvin, not F or C.

To increase the output of the thermocouple, increase the area of the junction between the dissimilar metals, heat the hot end more and cool the 'cold' side (one metal on each 'side'). The first will increase the amount of electricity, but not the efficiency, the second two will improve the efficiency.

The Stirling engine is a more complex bit of kit, but can be significantly more efficeient (e.g. 20-30% or more).

However, running your TV and DVD player from a candle just isn't going to happen. Not possible. There is just not enough power from the flame (approx 40 watts, so using a realistic 5% thermocouple, you get 2 watts of electricity).

It would be lovely to convert energy from one form to another very efficiently, but it is extremely difficult. It is easier and more efficient to go from a 'high level' energy type (Electricity) to a low form (heat, light) than it is to go the other way. This is because to go from heat to another form of energy, you have to make use of a heat engine (see above)- you can't just heat a wire and expect electricity.

The best heat engines of today- multi-stage steam turbines in power stations and 'Cathedral Diesels' (Huge, 15M tall, 50-100rpm ship diesels) work at about 50% efficiency.

[/geeky, boring scientist mode]

If you want 'clean' electricity and heat, then grow your own wood (e.g. short rotation willow coppice), and then use a wood gasifier. You can then use the wood gas to run a stirling engine or even an ICE to produce electricity. The waste heat from the engine's 'cold' side (exhaust, cooled end of Stirling or thermocouple) can then be used for domestic heating. There is a lot of work involved though.

James
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Old 8th February 2007, 11:03 PM   #6
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I think Jacques needs to tap into an otherwise wasted power source. Like water running down a drain or downspout or the heat that goes up the flue of a gas heater or little children and pets on a treadmill or something that gives infinite return as it is otherwise wasted. So far he has only requested the holy grail.

How many thousands of trained, skilled and forethinking individuals do you think are looking for the same thing right now? Jacques, if the things you are looking for existed, do you really think you'd find those ideas here? For free?

Shake thy head man.
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Old 9th February 2007, 04:48 AM   #7
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I seem to recall reading about some satellites that have a nuclear power generator that essentially just gets hot and is surrounded by many thousands of thermocouples to power the electronics on the thing. Don't ask me why they don't use solar panels...

I_F
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Old 9th February 2007, 08:11 AM   #8
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Quote:
Originally posted by I_Forgot
I seem to recall reading about some satellites that have a nuclear power generator that essentially just gets hot and is surrounded by many thousands of thermocouples to power the electronics on the thing. Don't ask me why they don't use solar panels...
Inverse square law (go twice the distance from the sun, get a quarter the power per square inch) kicks in with a vengeance past the orbit of Mars, plus it also works against you for radio transmitters.

Jupiter is a bit more than five times Earth's distance from the sun, so you get about 4% of solar power available here. It's worse for Saturn. Forget Uranus, and at Neptune the sun is merely a very bright star.
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Old 9th February 2007, 10:27 AM   #9
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Quote:
I seem to recall reading about some satellites that have a nuclear power generator that essentially just gets hot and is surrounded by many thousands of thermocouples to power the electronics on the thing. Don't ask me why they don't use solar panels...
Iím getting the idea NASA already solve the problem with thermocouples, because they have some clever people working at high peak and getting big pays to solve this kind of problems, 5% efficient for heat to electricity is just crap, useless
I know in todayís life, we are all generating electricity from motion, via alternators and spinning rotors, but one of the nice thing are starting to get popular, sonar energy, solid state, thatís nice man. Itís starting to get more efficient with our new technology in progress.

Quote:
How many thousands of trained, skilled and forethinking individuals do you think are looking for the same thing right now? Jacques, if the things you are looking for existed, do you really think you'd find those ideas here? For free?
Your right man, I probably wonít find a thing, what will give me more that 1 mA at 1700C, but maybe, you never know, just maybe someone founds the right thing, and decides to share it with us, that would be nice but not impossible.
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Old 9th February 2007, 10:30 AM   #10
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The Nasa thermocouples have the benefit of having an extremely low external temperature- about 3K. Also, they are inefficient, but they don't provide a lot of energy.

If you read my post, you will see that i suggest that you increase the surface area of your thermocouple, and cool one side of it to increase the output.

james
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