What do points 5-5b and 5b-6 represent in a gas turbine TS diagram?

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Homework Statement


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Homework Equations


N/A

The Attempt at a Solution


I am confused what 5-5b and 5b-6 represent in the above TS diagram. I know that 1-2 is compression, 2-3 is cooling, 3-4 is compression and 4-5 is regeneration (since these are indicated in the block diagram) but as for 5-5b and 5b-6 it is less clear. I mean 5-6 is the combustion chamber but what is the significance of the 5-5b and 5b-6 segments? Why have they split it up like this?
 
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Looking over the diagram perhaps if you can explain what's different between 7 and 7b, you might have your answer for 5b?

Beyond this I can't assist; I haven't looked at thermo since my student days.
 
NascentOxygen said:
Looking over the diagram perhaps if you can explain what's different between 7 and 7b, you might have your answer for 5b?

Beyond this I can't assist; I haven't looked at thermo since my student days.
Thanks for your reply. Unfortunately, I don't get that part either lol. Haven't encountered it in examples provided by my lecturer so far.
 
My guess is that if 6-7 represents the ideal heat exchange, then perhaps 6-7b represents a practical best attainable for that stage. You can't extract all of the heat in a heat exchanger.

I think the image you attached might be too large, it spills out and forces the rest of the page into small size.
 
My view was that 6-7 represents isentropic expansion in the turbine and 6 - 7b the actual expansion. So 5b might ne needed for the efficiency.