Flow Through Pipes MCQ with answer and solution

Concept

Hydraulic Diameter and Friction Loss in Non-Circular Conduits

Formula

hf = f (L / Dh) (V² / 2g), where Dh = 4A / P

Explanation

For non-circular pipes, friction loss in turbulent flow cannot be calculated using standard diameter, so it relies on the hydraulic diameter (based on cross-sectional area and wetted perimeter) along with internal surface roughness to determine the friction factor and head loss.

Shortcut

Remember: Non-circular conduits cannot use regular diameter, so turbulent friction loss always depends on Hydraulic Diameter (Dh) and Roughness.

Common mistake

Many students mistakenly assume that friction loss in non-circular conduits is always higher (Option D) or lower (Option C) than in circular conduits, or they overlook that the hydraulic diameter (Dh) is specifically used to account for non-circular cross-sectional geometry alongside roughness.