Thermoelectric devices and entropy

In summary, a thermoelectric device requires a temperature difference between two plates in order to work. Adding heat to a wire would violate the 2nd law of thermodynamics.
  • #1
mrblanco
5
0
Today in my thermodynamics class my professor spoke about how a process must satisfy the laws of thermodynamics in order to work. He gave an example of current going through a wire generating heat. (See attached picture) But he also talked about how adding heat to a wire and it generating a current would violate the 2nd law of thermodynamics. My question is, how does a thermoelectric device, which takes heat and turns it into a current, follow the 2nd law?
ImageUploadedByPhysics Forums1427315710.620976.jpg
 
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  • #2
Because thermoelectric devices require there to be a temperature difference between two plates. Go look it up and see what you find.
 
  • #3
I've looked it up and it seems to make sense, however, why would adding heat to a wire to produce a current not work? It seems like it would be the same process. If I'm adding heat then obviously there will be a temperature difference
 
  • #4
If you heat one end of a wire, there is an initial current : the electrons run away to the other end as much as they can. But you very soon (seconds) get equilibrium because the first ones push back (- charged) the rest, which are left to bake in the heat (they actually don't mind that much). You can't have current in an open circuit, so you're left with a voltage.
 
  • #5
Wouldn't that eventually happen in a TEG? The plates would eventually come to thermal equilibrium and there would no longer be a ΔT.
 
  • #6
mrblanco said:
I've looked it up and it seems to make sense, however, why would adding heat to a wire to produce a current not work? It seems like it would be the same process. If I'm adding heat then obviously there will be a temperature difference
The second law doesn't prohibit heat from producing electrical work, it just puts an upper bound on the amount of work that cAn be done. Thermoelectric devices operate well below that limit.
 
  • #7
mrblanco said:
I've looked it up and it seems to make sense, however, why would adding heat to a wire to produce a current not work? It seems like it would be the same process. If I'm adding heat then obviously there will be a temperature difference
A temperature difference between what and what? Obviously, the wire is the hot reservoir: where's the cold reservoir, how is heat flowing to it and how is your thermodynamic device getting in the way to harness/capture that flow?
 

1. What is a thermoelectric device?

A thermoelectric device is a type of technology that converts heat into electricity, or vice versa, through the use of a phenomenon called the thermoelectric effect. This effect refers to the generation of a voltage difference at the junction of two different types of materials when there is a temperature difference between them.

2. How does a thermoelectric device work?

A thermoelectric device consists of two different types of materials, usually semiconductors, that are connected at two junctions. When there is a temperature difference between the two junctions, electrons will flow from the hot to the cold junction, generating a voltage difference. This voltage difference can then be harnessed to create electricity.

3. What is entropy in relation to thermoelectric devices?

Entropy is a measure of the disorder or randomness of a system. In the context of thermoelectric devices, it is a key factor in determining the efficiency of the device. The higher the entropy, the lower the efficiency of the device.

4. What are the applications of thermoelectric devices?

Thermoelectric devices have a wide range of applications, including power generation, refrigeration, and temperature sensing. They are often used in situations where a reliable, compact, and efficient source of power or temperature control is needed, such as in space missions or remote locations.

5. Are there any limitations to thermoelectric devices?

While thermoelectric devices have many advantages, such as being environmentally friendly and having no moving parts, they also have some limitations. These include low efficiency compared to other power generation methods, high cost of production, and limited temperature range. However, ongoing research and technological advancements are continuously improving the performance of thermoelectric devices.

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