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Fluids rate of flow homework help

  1. Apr 17, 2012 #1
    1. The problem statement, all variables and given/known data

    Two cylindrical pipes both carry an ideal fluid (zero viscosity) in laminar flow. Pipe A has radius Ra = 2 and flow velocity Va = 8cm/s. Pipe B has radius Rb = 4cm and flow velocity Vb = 4cm/s.

    A) Calculate the cross section of pipe A and pipe B.
    B) Calculate the rate of flow in liters/second (1l = 1000cm cubic)

    2. Relevant equations

    maybe v1a1 = v2a2 ?

    3. The attempt at a solution

    v1a1 = v2a2
    = (8cm/s)(2cm) = (4cm/s)(4cm) = 1 ?

    It`s wrong.
     
    Last edited: Apr 17, 2012
  2. jcsd
  3. Apr 17, 2012 #2
    Re: Fluids

    okay. Now tell me what is a1, a2?
     
  4. Apr 17, 2012 #3

    tms

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    Re: Fluids

    Just what do [itex]a_1[/itex] and [itex]a_2[/itex] represent?

    Also, are these pipes connected end to end, or are they in parallel?
     
  5. Apr 17, 2012 #4
    Re: Fluids

    you mean...
     
    Last edited: Apr 17, 2012
  6. Apr 17, 2012 #5

    tms

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    Re: Fluids

    What has pressure got to do with it?

    Go back to your first equation: what is [itex]a_1[/itex]? This is not a trick question.
     
  7. Apr 20, 2012 #6
    Re: Fluids

    I have to calculate cross section of pipe A and B.

    My book says cross-sectional area is VA.

    I am confused with these formulas because I have the following:

    Flow rate = VA
    Flow rate = V/T

    So, flow rate = cross sectional area = VA?
     
    Last edited: Apr 20, 2012
  8. Apr 20, 2012 #7
    Re: Fluids

    R = 2 = area 1 = 4
    R = 4 = area 2 = 16
    ?
     
    Last edited: Apr 20, 2012
  9. Apr 20, 2012 #8
    Re: Fluids

    I think I know it...
     
    Last edited: Apr 20, 2012
  10. Apr 20, 2012 #9
    Re: Fluids

    would that be correct?
     
  11. Apr 20, 2012 #10
    Re: Fluids

    I just need this to finish my homework.
     
  12. Apr 20, 2012 #11
    Re: Fluids

    I think I know it:

    I think I am supposed to use pi. So, could it be: 3.14 x 4^2 = 50.24 for cross section pipe B?
     
    Last edited: Apr 20, 2012
  13. Apr 20, 2012 #12
    Re: Fluids

    I know the answer! I got the answer! I got the answer!! Just a question: how should I leave the flow rate considering the answer for B = 0.20096, should I say the answer is 0.20 or 0.200 l/s ?
     
  14. Apr 21, 2012 #13

    tms

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    Re: Fluids

    Assuming [itex]V[/itex] is volume and [itex]A[/itex] is area, something is wrong, either the book or your reading of it. The units are odd, too: [itex]\mathrm{L}^5[/itex]. If [itex]V[/itex] and [itex]A[/itex] mean something else, then I don't know.

    What is [itex]T[/itex]?

    Think units. What units must flow rate have?
     
  15. Apr 21, 2012 #14

    tms

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    Re: Fluids

    Since the problem, as you gave it, uses only one significant figure, then your answer should have no more than one significant figure.
     
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