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Registered Member #4266
Joined: Fri Dec 16 2011, 03:15AM
Location:
Posts: 874
Hi Just been wondering about themopiles and I'm abit stuck. Say you have 300W of input heat, and a themopile is 10% eff does that mean that you select a 30 watt pile...What happens if you get a 300watt pile, will that convert all the 300W into electrical power?
Registered Member #4266
Joined: Fri Dec 16 2011, 03:15AM
Location:
Posts: 874
Thanks Carbon Rod
Another question :) Say the pile datasheet say at 40C difference between the hotside and cold will make 30W and its 10% eff, if thats 300W about that needs to be taken from the cold side....The hotside is 40C and the cold is cold water at 20C making a difference of 20C, but the water is flowing fast enought to remove 600W, would the tempture of 20C be enought to make the 30W pile run at that power output, even thought the difference in temp is only 20C .
Registered Member #27
Joined: Fri Feb 03 2006, 02:20AM
Location: Hyperborea
Posts: 2058
Here is the formula you need:
Your efficiency only depends on the temperature difference as described in the formula. There is nothing you can do about it. If you think you can improve on it you will be considered to suffer from .
If the heat input is 300W and the pile delivers 30W into a load then the heat you need to remove from the cold side is 270W. Beyond that I don't think your question can be answered on a hypothetical basis. Also your numbers sound... optimistic. Last I looked hundreds of degrees could get 3% power into a load.
Registered Member #96
Joined: Thu Feb 09 2006, 05:37PM
Location: CI, Earth
Posts: 4062
Tin selenide (SnSe) is a new material and could exceed double the thermal efficiency of anything yet discovered, see arXiv..
Also thermophotovoltaic (TPV) systems are being investigated as a potential application, where the TPV cell is encapsulated in zinc selenide as it is transparent to long wave infrared.
"When the team at Northwestern tested it as a possible material for use in a thermoelectric generator they found it had the highest zT ever found, 2.6.
Registered Member #4266
Joined: Fri Dec 16 2011, 03:15AM
Location:
Posts: 874
Hi All Bjorn
Your efficiency only depends on the temperature difference as described in the formula. There is nothing you can do about it
Not explaining myself, I thought that the max efficiency of themopiles was 27% and read on here assumed a value of 10%,I'm not after efficiency, don't mind if the efficiency is 1%, but if a pile makes 30W at 40 degrees difference and is 5% efficiency, if I can remove 600W from the cold side, at a 20C difference dropping the efficiency down to 2.5%, will the fact that the 2.5% that gets through be removed quicker than one second say half a second ie J or W/sec Conundrum
Tin selenide
I think the piles do use that solder, you can't get them above 80C difference or the break with a max of 135C
Registered Member #96
Joined: Thu Feb 09 2006, 05:37PM
Location: CI, Earth
Posts: 4062
The piles probably use InSnBi or some variant, melting point is indeed around 135C. I doubt very much if you are using SnSe yet, as the effect was only discovered this year and previous cells either used PbTe or BiTe with a light doping of I believe yttrium to increase thermal figure of merit.
Registered Member #27
Joined: Fri Feb 03 2006, 02:20AM
Location: Hyperborea
Posts: 2058
Not explaining myself, I thought that the max efficiency of themopiles was 27% and read on here assumed a value of 10%,I'm not after efficiency, don't mind if the efficiency is 1%, but if a pile makes 30W at 40 degrees difference and is 5% efficiency, if I can remove 600W from the cold side, at a 20C difference dropping the efficiency down to 2.5%, will the fact that the 2.5% that gets through be removed quicker than one second say half a second ie J or W/sec
At 2.5% efficiency you are down to 15W usable power, and only if you add enough themopiles to move 600W at 20K delta.
There is no way of getting around the laws of physics and do it with one device.
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Question about themopiles and eff of device
