In turbulent flow, a rough pipe has the same friction factor as a smooth pipe____________________?

Correct answer: B. When the roughness projections are much smaller than the thickness of the laminar film

  • A. In the zone of complete turbulence
  • B. When the roughness projections are much smaller than the thickness of the laminar film
  • C. Everywhere in the transition zone
  • D. When the friction factor is independent of the Reynold's number

Explanation

When roughness projections are submerged within the viscous sublayer, they do not significantly affect wall resistance, so the pipe behaves hydraulically as smooth. This occurs when roughness is much smaller than the laminar-film thickness.

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