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Wall shear stress question

  1. May 10, 2008 #1
    fully developed flow liquid of dynamic viscosity 2.9x10^-3 Pa.s and relative density 0.9 in horizontal pipe of diameter 12mm, length of pipe=200mm and mean velocity is 0.5m/s

    To find the wall shear stress, i used τ=μ.du/dy = (2.9x10^-3)(0.5/0.012) = 0.121Pa

    The answer is 0.968Pa, where am i going wrong?

  2. jcsd
  3. May 10, 2008 #2
    What are the units of density?
  4. May 10, 2008 #3
    Make sure you are dimensionaly consistent and use the kinematic viscosity which is absolute viscosity/density.
  5. May 10, 2008 #4
    the density hasnt got any units, it just says the relative density. why should i be using the kinematic viscosity when the shear stress equation requires the dynamic viscosity, which is given
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