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Author Topic: How many thermocouples can be put in series?  (Read 16452 times)

Offline osocurious

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How many thermocouples can be put in series?
« on: 18/08/2010 04:22:46 »
Even the most efficient thermocouples produce minute amounts of electrical energy. However, if put into series as a thermopile they can generate more electrical energy. What I wanted to know is are there theoretical limits to how many thermocouples can be put in series? If one could, hypothetically, create a great column of thermocouples hooked in series could it generate a more substantial amount of energy? Or are there other forces that would come into play as the series gets larger?


 

Offline tommya300

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How many thermocouples can be put in series?
« Reply #1 on: 18/08/2010 06:47:30 »
Even the most efficient thermocouples produce minute amounts of electrical energy. However, if put into series as a thermopile they can generate more electrical energy. What I wanted to know is are there theoretical limits to how many thermocouples can be put in series? If one could, hypothetically, create a great column of thermocouples hooked in series could it generate a more substantial amount of energy? Or are there other forces that would come into play as the series gets larger?

http://en.wikipedia.org/wiki/Thermoelectric_effect
 

Offline Bored chemist

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Offline tommya300

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How many thermocouples can be put in series?
« Reply #3 on: 18/08/2010 08:30:17 »
 
Quote
Or are there other forces that would come into play as the series gets larger?

If this may help each terminating junction will hold a resistance that will add up,
Minimize this resistance by welding the terminating wire junctions together

If you use copper and constantan wire alloy, just need to weld each of the two opposing alloy in a cascade as many times as you need to obtain your goal.
« Last Edit: 18/08/2010 08:44:27 by tommya300 »
 

Offline osocurious

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How many thermocouples can be put in series?
« Reply #4 on: 18/08/2010 08:33:01 »
Those 2 links don't tell me anything I don't already know if you read my original question. I've read wikipedia, I'm not an idiot, or too lazy to do my own research.

What I can't find are physical limits. Would thousands or tens of thousands of thermocouples in series work, or does it create some resistive force that generates too much of it's own heat to properly allow temperature flow to work. No one is doing it...creating very large thermocouple arrays, I was wondering why. I know enough about Thermoelectric effects, I'm not looking for an education in that area.
 

Offline tommya300

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How many thermocouples can be put in series?
« Reply #5 on: 18/08/2010 14:53:55 »
.
Those 2 links don't tell me anything I don't already know if you read my original question. I've read wikipedia, I'm not an idiot, or too lazy to do my own research.

What I can't find are physical limits. Would thousands or tens of thousands of thermocouples in series work, or does it create some resistive force that generates too much of it's own heat to properly allow temperature flow to work. No one is doing it...creating very large thermocouple arrays, I was wondering why. I know enough about Thermoelectric effects, I'm not looking for an education in that area.

No intention to insult any one person's intelligent, and there was no intention previously.
With all due fairness to all, what investigations have you done?
So it can be seen by others, this way duplicate information will not provide an assumtion any intellegence is being offendeded.

OK do you have any electrical engineering knowledge.
Buffering each thermocouple from each other.
This would permit each units characteristic to freely operate within its own parameters without any other outside electrical inputs affecting it.
Now since we are looking at Milli to micro volts the buffers may load there units to a point that would offset the addition of the voltages of these cascading units.
Obviously the end product will resemble a closed circuit even if you just tie in a voltmeter across the whole lot.

http://www.electronics-tutorials.com/amplifiers/buffer-amplifiers.htm

If you can come up with a scheme that will self bias the buffer amps, this bias voltage needs to satisfy the buffer circuitry and balance the rest of the circuit outputs to obtain the goal of adding these individual voltages being produced from each thermocouple.
.

 
« Last Edit: 18/08/2010 15:00:48 by tommya300 »
 

Offline osocurious

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How many thermocouples can be put in series?
« Reply #6 on: 18/08/2010 18:07:54 »
Unfortunately no formal electrical engineering education. I went the software engineering route, but I follow a lot of what goes on and read a lot. I have a keen interest in solar power architectures, Stirling engines, thermo-electricity (and some related fields), and a variety of other things that I'm not formally educated in. I own and have tried to read newbielink:http://www.amazon.com/Thermoelectricity-Introduction-Principles-D-MacDonald/dp/0486453049/ref=sr_1_3?s=books&ie=UTF8&qid=1282143726&sr=1-3 [nonactive] . I understand a lot of it, but a lot also goes over my head right now. I've read (and re-read) everything available on wikipedia and some other science oriented sites. My curiosity has mostly been aroused by what *isn't* on the market, and massively serial thermopiles don't seem to be on the market. I was curious as to why. That is my main question I suppose.

The buffer you mention, that makes sense. But would the buffer need to be more of an electricity insulator or temperature insulator ? Which would I be more concerned with bleeding over between thermocouples? My guess is temperature, but something that is both electricity and temperature neutral would be best. Glass is a good electrical insulator, but not so good with temperature for example.
 

Offline tommya300

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How many thermocouples can be put in series?
« Reply #7 on: 18/08/2010 20:18:21 »
From what I understand here is your goal is to get the voltage producing characteristics of the thermocouple devices to add in cascade.

 It might be an unwanted interaction with eachother.
The word we need to focus on is isolation, not insulation.

 Any non passive device used in the buffering circuit will use some energy from an available source. Ideally from nothing external which would be defeating your purpose.

I use to think that something like this can be done with quartz radio that just needed a ground and an antenna which will provide a signal output to drive a piezo.
 

Offline Bored chemist

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How many thermocouples can be put in series?
« Reply #8 on: 18/08/2010 20:54:27 »
There are clearly theoretical limits to the number of thermocouples you can hook in series. For example, if you got enough of them together they would collapse into a black hole.
Similarly, if you only have this planet's resources to work with then there's a limit to what you can do. Eventually a stack of thermocouples might run into problems of electrical breakdown of the insulation, but that's probably not a practical consideration either.

On the other hand, if there had been a practical limit then it's possible that I might have mentioned it, rather than pointing out that stacks of a large number of thermo-junctions are already widely available (and, of course, you can hook them in series too).

It's true that the thermocouple has electrical resistance and this reduces the efficiency of the system but, if it turns out to be a problem you can connect them is series/ parallel arrays (or, as is equivalent) you can use bigger junctions made from thicker wire or whatever.
Adding a buffer amplifier just means you need another power supply; not very helpful in this case.
 

Offline tommya300

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How many thermocouples can be put in series?
« Reply #9 on: 19/08/2010 02:49:42 »
There are clearly theoretical limits to the number of thermocouples you can hook in series. For example, if you got enough of them together they would collapse into a black hole.
Similarly, if you only have this planet's resources to work with then there's a limit to what you can do. Eventually a stack of thermocouples might run into problems of electrical breakdown of the insulation, but that's probably not a practical consideration either.

On the other hand, if there had been a practical limit then it's possible that I might have mentioned it, rather than pointing out that stacks of a large number of thermo-junctions are already widely available (and, of course, you can hook them in series too).

It's true that the thermocouple has electrical resistance and this reduces the efficiency of the system but, if it turns out to be a problem you can connect them is series/ parallel arrays (or, as is equivalent) you can use bigger junctions made from thicker wire or whatever.
Adding a buffer amplifier just means you need another power supply; not very helpful in this case.
I do not know what the affects a collapse on a black hole or how it refers to the subject matter.

Quote
The thermoelectric generator
While the Seebeck voltage is very small (in the order of 10-70µV/°C), if the circuit's electrical resistance is low (thick, short wires), then large currents are possible (e.g. many amperes). An efficiency trade-off of electrical resistance (as small as possible) and thermal resistance (as large as possible) between the junctions is the major issue. Generally, electrical and thermal resistances trend together with different materials. The output voltage can be increased by wiring as a thermopile.

The thermoelectric generator has found its best-known application as the power source in some spacecraft. A radioactive material, such as plutonium, generates heat and cooling is provided by heat radiation into space. Such an atomic power source can reliably provide many tens of watts of power for years. The fact that atomic generators are highly radioactive prevents their wider application.


Wow this was an eye opener for me...
http://www.capgo.com/Resources/Temperature/Thermocouple/Thermocouple.html
 
Buffers are counter productive in this case.

How many thermocouples can be put in series?
Will depend on what goal you may want to reach.
The type of material the thermocouple alloys are and their characteristic.
What external heat source being applied. I thing in the terms of differential temperature.
From the looks of it the limit is in resources and cost overhead.
Is it economically fiesable, where is the gain?
« Last Edit: 19/08/2010 03:24:59 by tommya300 »
 

Offline osocurious

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How many thermocouples can be put in series?
« Reply #10 on: 19/08/2010 15:32:42 »
Thanks for that link. I hadn't seen that paper before.

My thoughts are purely blue-sky wonderings right now. I was fascinated by the idea of generating power from temperature differences and was exploring ways to create a constant temperature difference. Most literature on the effect marginalizes the benefit because of it's poor efficiency (5% to 10% is what I read) and it's very low output. But what intrigues me is the output is additive in series, and there doesn't seem to be a limit to the number in series. In programming we do a lot of things where a very small effect, done a tremendous number of times, has a perceived big effect. So my thinking was, so what if it's not efficient and has small output, put a lot of them together to boost the output, and the ability to harness temperature differences with no additional energy means it could have a net positive output.

So, blue-sky thought, what if you had a long pipe buried underground, the temperature on the outside of the pipe would be fairly constant. If done in arctic or volcanic areas you would even have a more extreme temp to work with. Then if you pumped water through the pipe at a different, controllable temperature, you would have a relatively cheap way to have a constant temperature differential. If that water was the runoff from some plant that super-heated it...even better.

Now, if the pipe was double hulled with a layer of thermocouples, hundreds of thousands of them in series, or mixed series/parallel inside the layer. They could tap into that temp differential. If the differential is small, say just 30 degrees C and the voltage for a thermocouple is micro or milli volts, would it matter if there were a massive number of them in play? It would still add up wouldn't it?

Anyway, thank you for indulging me my questions. I'm just curious about things and like to explore ideas.
 

Offline tommya300

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How many thermocouples can be put in series?
« Reply #11 on: 19/08/2010 17:46:22 »
Thanks for that link. I hadn't seen that paper before.

My thoughts are purely blue-sky wonderings right now. I was fascinated by the idea of generating power from temperature differences and was exploring ways to create a constant temperature difference. Most literature on the effect marginalizes the benefit because of it's poor efficiency (5% to 10% is what I read) and it's very low output. But what intrigues me is the output is additive in series, and there doesn't seem to be a limit to the number in series. In programming we do a lot of things where a very small effect, done a tremendous number of times, has a perceived big effect. So my thinking was, so what if it's not efficient and has small output, put a lot of them together to boost the output, and the ability to harness temperature differences with no additional energy means it could have a net positive output.

So, blue-sky thought, what if you had a long pipe buried underground, the temperature on the outside of the pipe would be fairly constant. If done in arctic or volcanic areas you would even have a more extreme temp to work with. Then if you pumped water through the pipe at a different, controllable temperature, you would have a relatively cheap way to have a constant temperature differential. If that water was the runoff from some plant that super-heated it...even better.

Now, if the pipe was double hulled with a layer of thermocouples, hundreds of thousands of them in series, or mixed series/parallel inside the layer. They could tap into that temp differential. If the differential is small, say just 30 degrees C and the voltage for a thermocouple is micro or milli volts, would it matter if there were a massive number of them in play? It would still add up wouldn't it?

Anyway, thank you for indulging me my questions. I'm just curious about things and like to explore ideas.
You are welcome I tripped over it.
I see that is resonable that they will add.
Remember this thermopile is in close proximity to the whole system. Its goal was to have a good power supply output in a rural area of outer space and have a long life span.


 Does not make it efficient or cost affective.
 It is just convienent to that particular net goal setup.
.
Making things long has its price.
« Last Edit: 19/08/2010 17:50:26 by tommya300 »
 

Offline John09

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How many thermocouples can be put in series?
« Reply #12 on: 20/08/2010 09:20:11 »
Hey thanks for the Wikipedia link. It will be useful to me.
 

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How many thermocouples can be put in series?
« Reply #12 on: 20/08/2010 09:20:11 »

 

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