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Homework Help: Fluid mechanics Reynolds number equation query

  1. May 9, 2009 #1
    1.I have been asked to:

    Calculate the density of a fluid if a ctitical velocity of 2m/s at Re=2000 in a pipe of bore 90mm at a dynamic viscosity oc 0.09cP

    I have calcualted the variables to SI units and found

    Um (V) =2m/s

    I am rearranging this formula
    http://www.rpgroup.caltech.edu/%7Enatsirt/aph162/webpages/F2WP2/reynoldsNumberFormula.png [Broken][/URL]

    3. The attempt at a solution

    [tex]\rho[/tex]= (Re*[tex]\mu[/tex])/(Um*D)

    I keep getting 1 as the answer for the density. Have I converted something to SI units incorrectly?

    Last edited by a moderator: May 4, 2017
  2. jcsd
  3. May 9, 2009 #2


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    Homework Helper

    1 what? Units please :biggrin:

    Also, why do you suspect 1 is wrong?
  4. May 9, 2009 #3

    That is a very low density.
  5. May 9, 2009 #4


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    Staff Emeritus
    Science Advisor
    Homework Helper

    That's comparable to air, which is 1.2 kg/m^3 under normal conditions (20 C, 1 atm)
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