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I Question about Jet engines (thermodynamics)

  1. Nov 21, 2016 #1
    Hi, I need help
    I got a project for school about jet engines. They say bysubstitution of equations 5.1, 5.2, 5.5 and 5.6
    butI don't know the steps how i get t0 the last formule.
    jet engine.png
    Thank you
    Maximilian Popelier
     
  2. jcsd
  3. Nov 21, 2016 #2

    DrClaude

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    Staff: Mentor

    Take eq. (5.7) and replace ##w_a## and ##q_a## by the right-hand side of (5.5) and (5.6), and then further simplify using (5.1) and (5.2).
     
  4. Nov 21, 2016 #3
    Tank you very much i will try it tomorrow
     
  5. Nov 22, 2016 #4
    hi thank you..
    but now i'm stuck here.... fysica.PNG
     
  6. Nov 22, 2016 #5

    DrClaude

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    You made a mistake in the numerator. After having corrected that mistake, before you use equations (5.1) and (5.2), notice that η is 1 - something, so try to get that 1.
     
  7. Nov 23, 2016 #6
    Im sorry I tried it but im again stuck at the next step...
     
  8. Nov 23, 2016 #7

    DrClaude

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    Please show your work.
     
  9. Nov 23, 2016 #8
    My whole Project or just the formule?
    Here is the formule: fysica.PNG
     

    Attached Files:

  10. Nov 23, 2016 #9

    DrClaude

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    You made a mistake in the last equality
    $$
    1 + \frac{-a}{b} = 1 - \frac{a}{b}
    $$
    $$
    1 + \frac{-a}{b} \neq 1 - \frac{a}{-b}
    $$
     
  11. Nov 23, 2016 #10
    owww... sorry but im still stuck fysicca.PNG
     

    Attached Files:

  12. Nov 23, 2016 #11

    DrClaude

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    You can now take out a factor in front of the fraction.
     
  13. Nov 23, 2016 #12
    How if i do it i have do divise the T1 by the Factor
     
  14. Nov 23, 2016 #13
    ficica.PNG
    i forgot the 1 -
     
  15. Nov 23, 2016 #14

    DrClaude

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    Take a factor out of the numerator only.
     
  16. Nov 23, 2016 #15
    oke and then?
     
  17. Nov 23, 2016 #16

    DrClaude

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    Then you should get eq. (5.8). You can write what you got in post #13 such that you get the same term in ##T_1## and ##T_3## in the numerator and the denominator.
     
  18. Nov 23, 2016 #17
    sorry i don't get it but i got this Capture.PNG
     
  19. Nov 23, 2016 #18

    DrClaude

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    Compare what is in the parenthesis with the denominator.

    I now see you also made a mistake when changing ##T_4## to ##T_3## in the numerator.
     
  20. Nov 24, 2016 #19
    Nice i got it!!
    Ty very much
     
  21. Nov 24, 2016 #20
    Oh i didn't get it i got a "-" wrong i will take a picture
     
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