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Fluid Mechanics
Flow Through Pipes
GATE 2015
Hard

For Fanning friction factor f (pipes) and drag coefficient CD (immersed bodies): P) f accounts only for skin friction, Q) CD accounts only for form friction, R) CD accounts for both skin and form friction, S) both f and CD depend on Re, T) for laminar pipe flow, f doubles on doubling flow rate. Which are TRUE?

  • AR, S, T
  • BP, Q, S
  • P, R, S
  • DP, Q, S, T

Explanation

f (pipe flow) is purely skin friction (P, true). CD (immersed bodies) includes BOTH skin and form drag, not just form (Q false, R true). Both depend on Re (S, true). For laminar flow f=16/Re∝1/Q, so f HALVES (not doubles) when Q doubles (T false). True: P,R,S.

Source: GATE CH 2015 (2015)

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