Understanding entropy generation

In summary, the speaker has been working on complex problems involving closed systems in thermodynamics and has some questions about entropy generation. They ask for clarification on whether Sgen is non-zero when work is done on a system and if quasi-static is equivalent to reversible. They also inquire about the circumstances in which it is safe to assume entropy generation is zero, mentioning heat transfer between objects with different thermal conductivity or heat capacities as one example.
  • #1
Urmi Roy
753
1
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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  • #2
i think Sgen is zero in a completely reversible process. S2-S1= dQ/T +Sgen
 

What is entropy generation?

Entropy generation is a concept in thermodynamics that refers to the process of converting useful energy into less useful forms, such as heat or waste energy. It is a measure of the disorder or randomness in a system.

Why is understanding entropy generation important?

Understanding entropy generation is important because it helps us to better understand and predict the behavior of physical systems, particularly in energy conversion processes. It also plays a crucial role in the second law of thermodynamics, which states that the total entropy of a closed system will always increase over time.

How is entropy generation calculated?

Entropy generation is typically calculated using the second law of thermodynamics, which states that the change in entropy of a system is equal to the heat transfer divided by the temperature at which the heat transfer occurs. This can be represented mathematically as ΔS = Q/T, where ΔS is the change in entropy, Q is the heat transfer, and T is the temperature.

What factors contribute to entropy generation?

There are several factors that contribute to entropy generation, including temperature differences, irreversible processes, and the presence of friction or resistance. In general, any process that involves the conversion of energy from one form to another will result in some level of entropy generation.

Can entropy generation be reduced or eliminated?

Entropy generation cannot be completely eliminated, as it is a fundamental process of thermodynamics. However, it can be reduced by minimizing temperature differences, using reversible processes, and reducing friction or resistance. This can lead to more efficient energy conversions and decreased waste heat.

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