Effect of change in Reynolds number on friction factor in turbulent flow - Fluid Mechanics

Q.  What is the effect of change in Reynold's number on friction factor in turbulent flow?
- Published on 05 Aug 15

a. As the Reynold's number increases the friction factor increases in turbulent flow
b. As the Reynold's number increases the friction factor decreases in turbulent flow
c. change in Reynold's number does not affect the friction factor in turbulent flow
d. unpredictable

ANSWER: As the Reynold's number increases the friction factor decreases in turbulent flow

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    Discussion

  • Pankaj   -Posted on 30 Sep 15
    Darcy-Weisbach formula for friction loss in pipe is given by,

    hf = (4 f L V2) / (2 g D)

    Where,
    f = Darcy's coefficient of friction.

    Sometimes this equation is also written as,

    hf = (f L V2) / (2 g D)

    Here, f is called as 'friction factor'.

    Friction factor = 4 x Darcy's coefficient of friction

    The friction factor depends upon,

    1. Reynold's number
    2. Relative roughness of pipe

    For laminar flow (Re < 2000),

    f = 16 / Re

    For turbulent flow (Re varying from 4000 to 105),

    f = 0.09 / Re1/4

    The friction factor decreases with increase in Reynold's number in turbulent flow.

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