Reversible cycles and entropy generation

[Urmi Roy]

I've got a couple of questions about reversible cycles:

So if we have two gaseous systems and have a reversible cycle working between them, then the entropy generation within each gaseous system is zero, right?

Do turbines execute reversible cycles?

Thanks a lot for your help!

 

[SteamKing]

I've got a couple of questions about reversible cycles:

So if we have two gaseous systems and have a reversible cycle working between them, then the entropy generation within each gaseous system is zero, right?

Do turbines execute reversible cycles?

Thanks a lot for your help!

Ideally, a turbine could be modeled as a reversible cycle, which means that the expansion of the working fluid would occur isentropically. In the real world, however, this is not the case, and there is an increase in the entropy of the working fluid as it moves through the turbine.

 

[Urmi Roy]

Ideally, a turbine could be modeled as a reversible cycle, which means that the expansion of the working fluid would occur isentropically. In the real world, however, this is not the case, and there is an increase in the entropy of the working fluid as it moves through the turbine.

Thanks for the reply SteamKing!

My point of confusion arose from the fact that in a discussion we were having at school,the fluid coming out of the turbine was used to fill an initially evacuated vessel.
I had a feeling that since the turbine operates a reversible cycle, the entropy generation in the vessel when the fluid got into it would be 0.

In a reversible cycle such as Carnot cycle, however, the entropy generation in all components, including the heat reservoirs would be zero...

However, as you mentioned, since the turbine operates in an open system, the entropy generation in the fluid as it moves through the turbine is zero. It is not necessary that the Sgen in the vessel is zero, even though it is directly connected to the reversible cycle...is that right?

 

[Chestermiller]

The word "cycle" means that the system comes back to its initial state over and over again. A cycle doesn't have to be reversible in order for this to happen, but, since entropy is a state function, the change in entropy must be zero for a complete cycle.

A turbine doesn't usually operate in a cycle, but it often does operate close to adiabatically and reversibly. So the change in entropy of the working fluid in passing through a turbine often is close to zero. However, this is usually not because it is operating in a cycle.

 

[sardar]

Reversible cycles are a fundamental concept in thermodynamics and play a crucial role in understanding the behavior of systems. In a reversible cycle, the system undergoes a series of changes and then returns to its original state without any net change in its surroundings. This means that the entropy generation within the system is zero, as you correctly stated.

Regarding your question about turbines, it depends on the specific conditions and design of the turbine. In an ideal scenario, where there is no friction or heat loss, a turbine can execute a reversible cycle. However, in reality, there will always be some degree of irreversibility and entropy generation in any system. Therefore, while turbines may not execute a completely reversible cycle, they can come close to it under certain conditions.

I hope this helps clarify your understanding of reversible cycles and entropy generation. Keep exploring and asking questions to deepen your understanding of these important concepts in thermodynamics.