Brayton Cycle modelling - optimum system design

  1. Hi

    I am trying to model the Brayton cycle in a gas turbine that is used for electricity generation.
    My main aim is to be able to fully power the x amount of daily electricity load of a building using this machine.
    In order to do this, is it correct to do a backwards model and find what specifications my generator must have that meet my power demand and match that with the work outout of the gas turbine.
    If so must I then equate the work required by the generator (using a product specification) with the work done by the turbine (include the losses as well). Can I then equate this with the work done by the compressor (and include the efficiencies) - I need to show what my work done and efficiencies are at each point of the cycle.

    I think I will then be able to find the optimum size of the gas turbine required to generate the torque required to rotate the electricity generator???

    Please let me know if my thinking is correct and if anybody can post the equations for work done and efficiency at each point of the cycle please.

  2. jcsd
  3. SteamKing

    SteamKing 10,985
    Staff Emeritus
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    Homework Helper

    I think your outlined approach is roughly correct. The electrical load will be determined by the anticipated power consumption requirements for the building. The generator which is sized to supply the power will have certain inherent losses in converting the mechanical power input to electrical output. Remember, the turbine's total power output is the sum of the compressor section's power input plus the required power input for the generator.
  4. thanks!

    I have not been able to find a schematic of the brayton cycle with all the neccessary equations. It would be extremely useful for me if you could help me construct one with the relevant equations of Temp, Pressure, efficiency, work done, power and efficiency.

    All I currently have is:

    Heat in to combustor - Q = m(h3-h1) h= entropy
    Work out of Turbine - Wt = m(h3-h4)
    Work into compressor - Wc = m(h1-h2)

    any ideas about the energy losses between the work out of turbine and the electrical generator? - what is the relationship between the gas turbine rotation (work done) and what is experienced by the generator.
  5. SteamKing

    SteamKing 10,985
    Staff Emeritus
    Science Advisor
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  6. haha thanks for the sarcasm SteamKing :P

    1) I am working with gas turbines for power generation and not thrust generation.
    2) I was basically asking for the main losses within the cycle and how to quantify these losses
    3) The reason being is because I then need to calculate how much torque my turbine must supply my generator to meet a 500kW peak load. Therefore if I can know the work done at the compressor and turbine and then find the efficiencies of the parts and the system as a whole and what the compression ratio is I can then choose what make/model of gas turbine I need !

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