A Moody diagram represents _____ as a function of Reynolds number, in a pipe flow.
- ALength of pipe
- Bfriction factorCorrect
- CKinetic head
- DFlow velocity
Solution
Concept
The Moody diagram plots the Darcy friction factor against Reynolds number for different relative roughness values (ε/D).
Formula
hf = f L V2 / (2 g D); laminar flow: f = 64 / Re
Step-by-step solution
1. A Moody diagram is a chart used in pipe flow problems. 2. The x-axis is Reynolds number (Re). 3. The y-axis is the Darcy friction factor (f). 4. Each curve is for one relative roughness (ε/D). 5. So the diagram shows friction factor as a function of Re. Answer is (B).
Explanation
The Moody diagram gives the friction factor f for a pipe when we know the Reynolds number and the relative roughness. We then use f in the Darcy-Weisbach equation to find head loss. It covers laminar, transition and turbulent flow zones.
Why the other options are wrong
A: Pipe length is not on the chart; it is used later in the Darcy formula. C: Kinetic head (V2/2g) is not plotted. D: Flow velocity is only part of Re; it is not the plotted quantity.
Shortcut
Moody = f vs Re (with ε/D curves).
Common mistake
Students think velocity or head loss is plotted directly, but the chart only gives f.
Correct answer: B) friction factor