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How can i solve these equations in Matlab?

  1. May 17, 2015 #1
    Equation 1: upload_2015-5-17_22-8-7.png
    Equation 2: upload_2015-5-17_22-8-24.png
    Equation 3: upload_2015-5-17_22-8-36.png
    Equation 4: upload_2015-5-17_22-8-47.png
    Equation 5: upload_2015-5-17_22-8-59.png

    I would like to solve upload_2015-5-17_22-9-25.png , (not the one with a star)
    and i want to define values for p, η0, ηr, θ0, θr.
    i have tried to solve them, but didn't work,
    can someone please help and show me step by step?
     
    Last edited: May 17, 2015
  2. jcsd
  3. May 17, 2015 #2

    phyzguy

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    Science Advisor

    What exactly are you trying to do? I count 10 unknowns (α, α*, p, η0, ηR, θ, θ0, S0, Z, β), and only 5 equations. So the system is underdetermined and there are an infinite number of possible solutions. You either need to fix some of the values or find more equations until the number of equations equals the number of unknowns. What exactly have you tried so far?
     
  4. May 17, 2015 #3
    Actually, i have values for p, η0, ηr, θ0, θr,
    for example:
    p=101325,
    η0=4.43,
    ηr=0.181,
    θ0=313.15,
    θr=373.15,
    also, as you can see, it is possible to solve α , because these 5 equations can be combined into 1
     
  5. May 17, 2015 #4

    phyzguy

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    Science Advisor

    OK, that makes more sense. So can you do the following?

    (1) Solve equation 4 for the ratio β/S0.
    (2) Divide equation 5 by S0 to get β/S0 on the LHS. Then plug the result from step 1 into this and solve this equation for Z.
    (3) Take the result from step 2 and plug it into equation 3, then solve this equation for α.

    Edit:

    Actually, I see now that it is even simpler than that. You can combine equations 4 and 5 to give:

    (1+5.1E-9*p)^Z = 1

    Solve this for Z and plug it into equation 3 to give α.
     
    Last edited: May 17, 2015
  6. May 17, 2015 #5

    phyzguy

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    Science Advisor

    Looking more at your equations. Equations 4 and 5 together imply that:

    (1+5.1E-9*p)^Z = 1

    Since p = 101325, (1+5.1E-9*p) = 1.0005, so this equation is only satisfied for Z = 0. Equation 3 then implies that α=0. Are you sure this is all correct, or am I missing something?
     
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