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Approximation of friction factor for Laminar Flow

  1. Sep 22, 2015 #1

    I read from Perry Green's ChE Handbook that the friction factor for Re ≤ 2,100 can be approximated by ƒ = 16/Re. But there was this question that I encountered (though I don't know the source) and according to it, ƒ = 64/Re for laminar flow. Can someone clarify which is which? Thank you!
  2. jcsd
  3. Sep 22, 2015 #2


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    The formula f=64/Re is called the Darcy friction factor and is derived from f=(Δp⋅2⋅D)/(L⋅ρ⋅u2)

    The formula f=16/Re is called the Fanning friction factor and is derived from f=(Δp⋅R)/(L⋅ρ⋅u2)

    Basically they are the same, but different values/dimensions are used to define them
  4. Sep 22, 2015 #3
    I see. That's really confusing. Anyway, thank you!
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