Understanding entropy generation

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SUMMARY

This discussion focuses on entropy generation (Sgen) in thermodynamic systems, particularly in closed systems. It clarifies that when work is done on a system, such as in an adiabatic process with a paddle wheel, Sgen can be non-zero despite no entropy transfer. The conversation also establishes that quasi-static processes are equivalent to reversible processes, where Sgen is indeed zero. Additionally, it addresses the conditions under which Sgen can be assumed to be zero, specifically highlighting scenarios involving heat transfer between objects with differing thermal properties.

PREREQUISITES
  • Understanding of thermodynamic principles, specifically closed systems.
  • Familiarity with concepts of entropy and entropy generation (Sgen).
  • Knowledge of adiabatic processes and their implications in thermodynamics.
  • Basic grasp of reversible and quasi-static processes in thermodynamic systems.
NEXT STEPS
  • Study the laws of thermodynamics, focusing on entropy and its implications in closed systems.
  • Explore the concept of adiabatic processes in greater detail, including mathematical formulations.
  • Research the conditions under which Sgen can be considered negligible in various thermodynamic scenarios.
  • Learn about the differences between reversible and irreversible processes in thermodynamics.
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Students and professionals in thermodynamics, mechanical engineers, and anyone involved in energy systems analysis or thermal management.

Urmi Roy
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Hi all,

I've been doing some pretty complex problems on closed systems in thermodynamics, and a few questions pooped up in my mind about Sgen (entropy generation). Please help me out with them..

1. When work is done on a system (like a paddle wheel in a cylinder containing gas), there is no entropy 'transfer' but is Sgen non zero? Then the 'entropy change' that we get from the constitutive relations for entropy change is wholly Sgen?

An interesting example of this an adiabatic process, where an insulated piston-cylinder system experiences work from outside, and the gas is compressed.

2. Is quasi-static equivalent to reversible? Is Sgen zero for quasi-static/reversible process?

3. Under what circumstances is it safe to assume entropy generation is 0? I usually assume so when there is heat transfer between 2 objects that have very different thermal conductivity or hear capacities...is that ok? Is there any additional situation?

Thanks!
-Urmi
 
Last edited:
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i think Sgen is zero in a completely reversible process. S2-S1= dQ/T +Sgen
 

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