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How to design an industrial ducting system - Duct Velocities

Feb 14

How to design an industrial ducting system - Duct Velocities

No matter if you're looking at installing ducting Columbus systems or changing an existing one, the top priority should be to ensure your system runs efficiently and costs as low as possible. It's not cheap to install a ducting system. You want to make sure that you are only buying what you really need. Columbus Airduct Cleaners can help you do accurate calculations based on your dust velocity.

Determine Dust Velocity

The material that is being transported through the duct will determine the velocity within the section. The diameter of the conduit determines the required airflow (measured in cubic feet per second (cfm). A minimum velocity is necessary for systems handling particles. This will prevent particulate from falling out of the airstream and eventually settling on the duct. Unusually high velocity could cause duct abrasion and waste of power.

The following equation describes the relationship between the airflow Q, duct velocity  (v), and duct diameter  (d) in a section of a ducting network:

Q = A * v, where A = p * d2 / 4 or,


Q = (p * d2 / 4) * v

This equation will calculate the Air Flow required to maintain a given duct speed (v) or duct size (d). You would need to have 9 inches (0.75 ft.), diameter ducts that move at 4000 feet per min (fpm).

Q = (p * (0.75 ft.)2 / 4) * (4000 ft./min) = 562.5 cfm

Use the following equation to calculate the velocity (v), for a system that has an Air Flow (Q), through a section or duct with a diameter (d).

v = (4 * Q) / (p * d2)

A fan with 600 cfm would mean that the air velocity through a 6in. This would give you a 0.5-foot diameter duct:

v = (4 * 600) / (p * (0.5)2) = 3056 fpm

You can use the following equation to calculate the duct diameter (d), required for a velocity(v) of a fan providing an airflow (Q), or the equation:

d = (4 * Q) / (p * v)

For example, the diameter of a duct required to achieve 4000 fpm velocity with a system that has a 1000 cfm flow would be:

d = (4 * 1000) / (p * 4000) = 0.564 feet or 6.77 inches

You will need to reduce the duct size to reach the 4000 fpm speed, which is 6 inches.

You can save money and ensure your ducting system works at its best.


Columbus Airduct Cleaning

Columbus, OH

(740) 291 0950