Fluid Mechanics - Mechanical Engineering (MCQ) questions and answers for Q. 3918

Q.  What is Darcy-Weisbach formula for heat loss due to friction?

f = Darcy's coefficient of friction

- Published on 04 Aug 15

a. hf = (f l V2) / (g d)
b. hf = (f l V2) / (2 g d)
c. hf = (4 f l V2) / (2 g d)
d. hf = (16 f l V2) / (2 g d)

ANSWER: hf = (4 f l V2) / (2 g d)


  • abhilash   -Posted on 20 Aug 17
    IT IS fLV^2/2gD where f-Darcy's wiesbach friction factor
    4fLV^2/2gD where f-fannings friction factor
  • Pankaj   -Posted on 21 Oct 15
    - The Darcy-Weisbach formula contains a dimensionless friction factor which is called as Darcy friction factor, resistance coefficient or simply friction factor

    It is often that the head loss in hydraulic engineering applications is expressed in terms of volumetric flow rate in the pipe. For this, it is accessory to substitute the following equation into the original head loss form of the Darcy-Weisbach formula.

    u2 = (Q)2 / (Aw)2


    u = the average flow velocity, m/s

    Q = the volumetric flow rate, m3/s

    Aw = the cross-sectional wetted area, m2
  • Pankaj   -Posted on 30 Sep 15
    While fluid flowing through a pipe, some energy gets lost in order to overcome hydraulic resistance. These energy losses in are classified into two categories as follows:

    1. Major losses
    2. Minor losses

    Major losses occur due to friction in pipe and are given by Darcy-Weisbach formula.

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

    and minor losses occur due to disturbance in the flow pattern such as sudden contraction or expansion in pipe, valves, bends etc

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