Question

For laminar flow in a pipe carrying a given discharge, the height of surface roughness is doubled. In such a case, Darcy-Weisbach friction factor will

• A. Remain unchanged
• B. Be halved
• C. Be doubled
• D. Increase fourfold

Answer 1

The correct option is A Remain unchanged

Laminar flow is governed by Reynolds number only and the Darcy-Weisbach friction factor in the case of pipe flow is

$f=\frac{64}{Re}$

So flow will remain unchanged.