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

AI Thread Summary
The discussion centers on a hypothetical scenario involving an infinite cylinder filled with monoatomic gas, where heat is supplied to expand the gas and do work via a piston. The main question raised is whether this setup violates Kelvin's statement of the second law of thermodynamics, particularly since it seems to allow for the conversion of heat into work without a cyclic process. Participants argue that working with infinite systems leads to contradictions, especially regarding energy extraction and entropy. The conversation also touches on the implications of using a finite cylinder and the role of heat supply methods in the overall efficiency of energy conversion. Ultimately, the feasibility of achieving nearly 100% efficiency in such scenarios is questioned due to the inherent complexities of thermodynamic principles.
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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