What Happens to the Work Output in a Carnot Cycle?

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Discussion Overview

The discussion revolves around the work output in a Carnot cycle, particularly focusing on the isothermal expansion phase and the role of heat transfer in relation to work done. Participants explore the implications of the first law of thermodynamics in this context, as well as the functionality of components like boilers in heat engines operating under a Carnot cycle.

Discussion Character

  • Technical explanation, Conceptual clarification, Debate/contested

Main Points Raised

  • One participant questions why the work done during the isothermal expansion does not count toward the total work output of the cycle.
  • Another participant asserts that, according to the first law of thermodynamics, the heat transferred in a cycle is equal to the work done, as the change in internal energy is zero.
  • A follow-up inquiry addresses the scenario of a boiler in a heat engine, questioning whether it performs work since it is rigid and does not have a piston, and how it maintains isothermal heat transfer.
  • A later reply asks about the purpose of the steam from the boiler, implying a need for clarification on its role in the cycle.

Areas of Agreement / Disagreement

Participants express differing views on the role of work done during the isothermal expansion and the function of the boiler, indicating that multiple competing perspectives remain unresolved.

Contextual Notes

Participants reference the first law of thermodynamics and its application to the Carnot cycle, but there are unresolved questions regarding the assumptions about work and heat transfer in rigid systems like boilers.

Red_CCF
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Hi

From http://en.wikipedia.org/wiki/Carnot_cycle

"Reversible isothermal expansion of the gas at the "hot" temperature, TH (isothermal heat addition). During this step the expanding gas makes the piston work on the surroundings. The gas expansion is propelled by absorption of quantity Q1 of heat from the high temperature reservoir."

I was wondering why the work done on the surroundings at this stage does not count toward the total work output of the cycle and why it is not used?

Thanks
 
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It does.

In fact, from the first law of thermodynamics, you can make Heat = Work + Delta U, though as it is a cycle and U is a state variable, Delta U in the cycle is null, so the heat transferred is equal to work.
 
Hobold said:
It does.

In fact, from the first law of thermodynamics, you can make Heat = Work + Delta U, though as it is a cycle and U is a state variable, Delta U in the cycle is null, so the heat transferred is equal to work.

Hi, thanks for the response

What about for a boiler? A boiler in a heat engine operating a Carnot cycle does not have a piston (it is rigid), in this case, although it is also responsible for Process 1-2 in a Carnot cycle it does no work right? Also, how does a rigid boiler maintain isothermal heat transfer?

Thanks
 
does the steam from the boiler go anywhere and do anything?
 

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