Entropy Changes in Reversible Engines: Is the Total Change Always Zero?

[KFC]

I learned Thermodynamics long time ago, forgot most of the content. I just want to ask I question.

For a reversible engine, no matter how many complete cycles it done, the total change of entropy of the engine will always be ZERO, right? What about the change of entropy of the universe in this case? Also ZERO?

 

[p.tryon]

Would this be a combustion engine?

 

[KFC]

Would this be a combustion engine?

I don't know, it is a conceptural question, no other detail. I read some book to review therodynamics and stat. mech. , some material said for reversible process, to complete one cycle, nothing change, the change of entropy is ZERO. Just want to confirm that.

 

[LURCH]

I learned Thermodynamics long time ago, forgot most of the content. I just want to ask I question.

For a reversible engine, no matter how many complete cycles it done, the total change of entropy of the engine will always be ZERO, right? What about the change of entropy of the universe in this case? Also ZERO?

That depends no whether the universe is reversable (oscilating nuiverse) or non-reversable (heat-death). Current observations suggest that the latter is the case, so entropy just contiues increasing 'till it reaches maximum, when no more energy can flow from one place to another. At this point, the universe will be a fairly homogenous low-density cloud of energy.

 

[KFC]

That depends no whether the universe is reversable (oscilating nuiverse) or non-reversable (heat-death). Current observations suggest that the latter is the case, so entropy just contiues increasing 'till it reaches maximum, when no more energy can flow from one place to another. At this point, the universe will be a fairly homogenous low-density cloud of energy.

I completely have no idea of this. So what about the system itself, will entropy change?

 

[p.tryon]

I don't know, it is a conceptural question, no other detail. I read some book to review therodynamics and stat. mech. , some material said for reversible process, to complete one cycle, nothing changes, the change of entropy is ZERO. Just want to confirm that.

This seems reasonable. If there is no change in the engine, there will be no change in entropy of the engine system. However, I am struggling to imagine an engine that does not involve some type of change.

 

[KFC]

This seems reasonable. If there is no change in the engine, there will be no change in entropy of the engine system. However, I am struggling to imagine an engine that does not involve some type of change.

Like carnot engine? But this is a very ideal case, textbook said there is no engine with efficiency larger than that of carnot engine, does that mean practical engine will never be reversible?

 

[p.tryon]

Yes and saying that a real engine can not be thermodynamically reversible is the same as saying it can not be 100% efficient. In theory it is possible but in practice it is impossible because in a working engine there will always be friction...etc...