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Thread: Solving for other variables.

  1. #1
    PLC
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    Solving for other variables.

    Hoping someone can help me with this. Trying to solve for other variables from this equation, not sure where to start.

    Flow=((0.036*0.85*169.65*SQRT(2*( P *2.48843)*(1+51.6/273)/1.72/(1-(14.7/150)^4))*48)*(273/(273+51.6))

    So right now if I calculate with P being 5, you should get a flow of 655. I need to reverse this to enter the pressure and it give me the flow.

    Hopefully that makes since.

    Thank you for you time.

    PLC
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  2. #2
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    Re: Solving for other variables.

    Hey PLC.

    Try showing us the algebra you use to go from Flow(P) to P(Flow).

    Most of it will just be tedious operations and eventually you should be able to get the expression for P(Flow).
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  3. #3
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    Re: Solving for other variables.

    Quote Originally Posted by PLC View Post
    Hoping someone can help me with this. Trying to solve for other variables from this equation, not sure where to start.

    Flow=((0.036*0.85*169.65*SQRT(2*( P *2.48843)*(1+51.6/273)/1.72/(1-(14.7/150)^4))*48)*(273/(273+51.6))
    The first thing I would do is the indicated arithmetic that does NOT involve P:
    0.036*0.85*169.65= 4.88529. 1+ 51.5/273= 1.1886446886446886446886446886447, 1- (14.7/150)^4= 0.999907763184 and 273+ 51.6= 324.6.

    Unfortunately I do not know what you mean by "(1+51.6/273)/1.72/(1-(14.7/150)^4))". Since division is not "associative", a/b/c could mean either (a/b)/c or a/(b/c) and those are not the same. Which do you mean?

    So right now if I calculate with P being 5, you should get a flow of 655. I need to reverse this to enter the pressure and it give me the flow.
    What you have now lets you "enter the pressure" and gives "flow". Did you mean "reverse this to enter flow and it gives me the pressure"? In any case, it is impossible until you have clarified the division.

    Hopefully that makes since.

    Thank you for you time.

    PLC
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  4. #4
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    Re: Solving for other variables.

    Agree with Halls...
    Replacing P with 5, Wolfram shows flow = 869:

    Wolfram|Alpha: Computational Knowledge Engine
    Last edited by DenisB; Jun 9th 2017 at 06:39 AM.
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  5. #5
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    Re: Solving for other variables.

    I suspect that is a problem of the interpretation of "(1+51.6/273)/1.72/(1-(14.7/150)^4))*48)*(273/(273+51.6))", as to whether that "double division", a/b/c, is to be interpreted as (a/b)/c or as a/(b/c). I was hoping PLC would let us know which was intended.
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  6. #6
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    Re: Solving for other variables.

    Flow=((0.036*0.85*169.65*SQRT(2*( P *2.48843)*(1+51.6/273)/
    1.72/(1-(14.7/150)^4))*48)*(273/(273+51.6))

    To start, a ")" is missing: there are 9 "(" and 8 ")".

    In my opinion, that is a ridiculous presentation of the "formula".
    I would "go at it" a bit like this:
    a = 0.036*0.85*169.65
    b = 2.48843
    c = 1+51.6/273
    d = 1.72
    e = (1-(14.7/150)^4)*48
    f = 273/(273+51.6)

    F = [a*SQRT(2*P*b)*c] / [d/(e*f)]

    Then solving for P is much easier...
    Last edited by DenisB; Jun 9th 2017 at 12:23 PM.
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