Possible violation of the Kelvin statement (2nd law)?

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    2nd law Kelvin Law
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Discussion Overview

The discussion revolves around a hypothetical scenario involving an infinite cylinder filled with monoatomic gas and the implications of supplying heat to it, particularly in relation to the Kelvin statement of the second law of thermodynamics. Participants explore the theoretical conversion of heat energy into work and the conditions under which this might occur, including considerations of infinite systems and entropy.

Discussion Character

  • Debate/contested
  • Conceptual clarification
  • Exploratory

Main Points Raised

  • One participant suggests that supplying heat to an infinite cylinder allows for the complete conversion of heat energy into work, potentially violating the Kelvin statement, assuming zero friction.
  • Another participant questions the practicality of the scenario, arguing that working with infinite systems leads to contradictions and that heating may not be necessary to extract energy.
  • A follow-up inquiry considers the implications if the cylinder were very long but finite, asking whether all supplied heat could be converted to work in that case.
  • Participants introduce the concept of a perfect vacuum at zero temperature as a potential cold reservoir, suggesting that this could allow for nearly 100% efficiency in converting heat to mechanical power.
  • Concerns are raised about the method of supplying heat and the associated increase in entropy, with one participant expressing a lack of familiarity with the concept of entropy and its relevance to the discussion.

Areas of Agreement / Disagreement

Participants express differing views on the feasibility and implications of the proposed scenario, with no consensus reached on whether the situation described could violate the Kelvin statement or the validity of using infinite systems in thermodynamic discussions.

Contextual Notes

Participants note the dependence on the definitions of infinite systems and the assumptions regarding heat supply and entropy, which remain unresolved in the discussion.

weezy
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Say I have an infinite cylinder filled with monoatomic gas and on one end has a piston attached to it. I now supply heat to the cylinder. The gas expands thereby converting all of heat energy into physical work(displacement of the piston). Since the cylinder is very long it eliminates the requirement of a cyclic process and could in theory provide work for a very long time until the piston reaches the cylinder's length. Have I not just violated kelvins statement? Provided friction is zero? W=P.dV?
 
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Why bother heating it? You have an infinite amount of energy stored in your cylinder, you can easily extract a finite amount out of it without changing the system.
Working with infinite things just doesn't work.
 
mfb said:
Why bother heating it? You have an infinite amount of energy stored in your cylinder, you can easily extract a finite amount out of it without changing the system.
Working with infinite things just doesn't work.
What if it was very long but finite? Wouldn't then all the Q I supply be converted to work?
 
If you have an infinite vacuum of zero temperature available, and infinite time for the process.
 
How are you supplying heat though? A flame, electricity, a hamster on a wheel? That is where the increase in entropy is occurring here.
 
DuckAmuck said:
How are you supplying heat though? A flame, electricity, a hamster on a wheel? That is where the increase in entropy is occurring here.
I still haven't been exposed to the idea of entropy yet. Basically I mean that if the cylinder is very long for some finite amount of time I could get all of the heat energy to be expand the gas and thereby converting "all" heat into work.
 
If you have a perfect vacuum (or anything else) at zero temperature as cold reservoir, you can convert heat to mechanical power with an efficiency of (nearly) 100%.
 

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