Entropy: Understanding the Cycle | Thermodynamics

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SUMMARY

In thermodynamics, the concept of entropy is crucial for understanding isolated systems and cyclic processes. In an isolated system, entropy can only remain constant or increase, but for a thermodynamic cycle represented on a PV diagram, the entropy returns to its initial value after each cycle. This indicates that while the entropy of the universe may increase due to work dissipation or heat transfer, the entropy of the system itself does not accumulate indefinitely through repeated cycles. Thus, the law of entropy applies consistently to cyclic processes.

PREREQUISITES
  • Understanding of thermodynamic cycles
  • Familiarity with PV diagrams
  • Knowledge of the laws of thermodynamics
  • Concept of entropy as a state function
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  • Study the implications of the second law of thermodynamics
  • Explore the concept of work dissipation in thermodynamic systems
  • Learn about heat transfer and its effects on entropy
  • Investigate real-world applications of cyclic processes in engineering
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Students and professionals in physics and engineering, particularly those focusing on thermodynamics, energy systems, and entropy analysis.

Tikkelsen
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I'm having trouble getting my head around entropy. In an isolated system, entropy can only remain the same or increase. Is this the same for a thermodynamics cycle? What I mean is, if I drew a cycle on a PV diagram, would the entropy keep increasing? I can't see how that would work, that would mean I would have infinite entropy if I run the cycle an infinite number of times
 
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Thermodynamic entropy is a function of state. Cyclic process returns system into the same state all over again. So the value of entropy returns to the initial value as well.
 
Tikkelsen said:
I'm having trouble getting my head around entropy. In an isolated system, entropy can only remain the same or increase. Is this the same for a thermodynamics cycle? What I mean is, if I drew a cycle on a PV diagram, would the entropy keep increasing? I can't see how that would work, that would mean I would have infinite entropy if I run the cycle an infinite number of times


The entropy of the system undergoing the cycle would be the same after every cycle. If you have work dissipation or heat transfer between finite temperature differences then the entropy of the universe increases. So yeah the law of entropy applies perfectly to cycles.
That being said, what's the problem with the entropy increasing without bound if you run the cycle many times? entropy increases or remains the same, there's no upper limit to the amount of entropy that can be created in the universe.
 

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