How do I calculate lines of constant pressure in a Brayton cycle diagram?

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SUMMARY

This discussion focuses on calculating lines of constant pressure (isobars) in Brayton cycle diagrams, specifically for jet engine efficiency studies. The user is familiar with basic isentropic relationships and entropy calculations but seeks guidance on deriving isobaric lines. Key processes include compression, where pressure and temperature increase while entropy remains constant, and heat addition, which alters temperature and entropy. The correct formula for entropy change during fuel addition is identified as delta S = q * LN(T2/T1).

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  • Understanding of Brayton cycle principles
  • Familiarity with Temperature-Entropy diagrams
  • Knowledge of isentropic relationships in thermodynamics
  • Basic calculus for handling logarithmic functions
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  • Research methods for calculating isobaric lines in Temperature-Entropy diagrams
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Students and professionals in aerospace engineering, thermodynamics enthusiasts, and anyone involved in optimizing jet engine performance through Brayton cycle analysis.

ingmarvandijk
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Hey guys (and girls?)

I'm new here, just registered, because I have a problem that my textbooks or google can't help me with:

I am making "Brayton cycle diagrams" for a study in jet engine efficiency. It's basically a Temperature - Entropy diagram for those of you who are unfamiliar with it. I know how to calculate the temperature increase with a pressure increase (basic isentropic relationships), and the entropy increase with fuel addition (delta S = q * LN( delta T)).

The problem I'm having is calculating lines of constant pressure in this diagram. Every source talks about them, but no source tells me how to calculate them. I know they are supposed to be increasing curves (the temperature difference for a pressure ratio is higher at higher entropy).

Does anyone have a clue to calculate these isobars?

Any help is greatly appreciated!
 
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Some extra insight:

There are 2 important processes.
The first one is compression, where the pressure increases, the temperature as a result, and the entropy remains constant.
The second process is heat addition (or subtraction) where the temperature changes and the entropy follows

Also, in the formula for fuel addition it should of course be LN(T2/T1) instead of Delta T.
 
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