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Fluid Mechanics and Hydraulic Machinery Miscellaneous

Fluid Mechanics and Hydraulic Machinery

  1. Consider fully developed flow in a circular pipe with negligible entrance length effects. Assuming the mass flow rate, density and friction factor to be constant, if the length of the pipe is doubled and the diameter is halved, the head loss due to friction will increase by a factor of
    1. 4
    2. 16
    3. 32
    4. 64
Correct Option: D

Head loss =
fLv2
=
fl(Q/A)2
2gd2gd

⇒  Head loss ∝
L
d5

h1*
L
d5

h2*
2.L
=
L
× 64
(d/2)5d5

h1
= 1/64 ⇒ 
h2
= 64
h2h1



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