Is it possible to extract the molecular kinetic energy from a system directly (without the use of a heat engine / temperature gradient) and convert that to
another form of energy, such as electricity, or perform useful work?
Similar questions have been asked before:
- Extracting heat energy from a material
- Can you extract energy from "hot" things without a temperature differential?
However, I find the answers slightly lacking. They rest on one of two assumptions:
- that the asker wants to transfer the heat away through a heat engine; or
- that the Second Law of Thermodynamics applies to all systems in all situations —
my understanding of thermodynamics (albeit rather limited) says that these
laws are statistical properties that are true en masse, but not absolute laws of nature in the sense that they apply to all systems for arbitrarily short amounts of time.
Even if my understanding of the second law is incorrect, I don't understand why we can't extract heat energy from an object without a temperature gradient by placing it under certain conditions. For example, heat transfer via infrared radiation could be extracted from a gas of any temperature, placed in a glass sphere and isolated from the environment via a vacuum chamber:
The gas would slowly radiate its heat through the glass to the ambient container housing the vacuum, and solar panels lining this surface could feasibly collect this energy.
Note that this isn't a question about efficiency; I'm not concerned with how efficient this particular setup would be. It seems that if it works at all, one would be extracting thermal energy from an object without a heat engine.
Best Answer
"The gas would slowly radiate its heat through the glass to the ambient container housing the vacuum, and solar panels lining this surface could feasibly collect this energy."
No. If we assume the gas inside and the cells outside are both at temperature $T$, then no (thermal) energy can be extracted. They will be in thermal equilibrium. Whatever mechanism you want to come up with will be unable to extract energy.
If we assume some pathway that interacts with the IR radiation to complete a chemical reaction, then since the material is at that temperature, the reaction is just as likely to run in reverse and return the same radiation to the interior.