Mechanical Engineering

Fluid Mechanics : Moody's Diagram

Moody’s diagram is used to compute for the friction factor in the pipe that a working fluid flows across.

Friction factor is dependent on the following:

• Roughness of the pipe: dependent on the piping material
• Diameter of the cross-section of the flow
• Velocity of the flow
• Kinematic viscosity of the working fluid

The friction factor is a function of both Reynold’s Number of the working fluid and relative roughness of the pipe.

The Moody diagram looks like this:

Tips for quick estimation on Friction Factor

Apply the following procedures to compute friction factor in a timely manner:

i) Calculate the Reynold’s number(Re) of the flow to analyze the type of flow

ii) If Re>2000, calculate the relative roughness of the pipe. If Re<2000, then friction factor is equal to 64/Re

iii) Highlight the entire curve closest to the relative roughness of the pipe.

iv) Using a ruler, extend a vertical line from Re to see where it intersects with the highlighted curve. Make a large mark on the intersection

v) Using a ruler, extend a horizontal line to the left from the point of intersection from step iv)