Section 4: Soil and Water Conservation Engineering
Fluid Mechanics
Subtopic: Laminar and turbulent flow in pipes, Darcy–Weisbach and Hazen–Williams equations
Question Statement:
In the Moody diagram, the third parameter is ε/D. Here, ε is
Options:
(A) the equivalent uniform sand grain roughness
(B) an arbitrarily chosen roughness magnitude
(C) median size in a non-uniform sand grain roughness
(D) mean height of the actual roughness of commercial pipes
Official Answer Key:
A
Step-by-Step Solution & Explanation
ε is Nikuradse's equivalent sand-grain roughness — the roughness height of uniform sand grains that would produce the same friction factor as the actual (commercial) pipe surface; it is used to non-dimensionalise as relative roughness ε/D on the Moody chart.
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