Duct Velocity

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The velocity in ventilation ducts can be calculated in imperial or SI units.

Duct Velocity in Imperial Units

The velocity of air in a ventilation duct can be expressed in imperial units like

v_i = q_i / A_i

    = 576 q_i / (π d_i²)

    = 144 q_i / (a_i b_i)         (1)

where

v_i = air velocity (ft/min)

q_i = air flow (cfm)

A_i = area of duct (square feet)

d_i = diameter of duct (inches)

a_i = width of duct (inches)

b_i = width of duct (inches)

Example - Air Flow Velocity in a Duct

The velocity in a 12 inch duct with air flow 1000 cfm can be calculated as

v_i = 576 1000 (cfm) / (π (12 in)²)

   = 1273 (ft/min)

Air Flow Velocity Calculator - Imperial Units

Air velocity can be calculated with the calculator below. Add air volume - q - and diameter - d - (or length a and b).

Related Mobile Apps from The Engineering ToolBox

• Air Duct Flow App
• Air Duct Velocity App
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- free apps for offline use on mobile devices

Duct Velocity in SI - Units

Air velocity in a duct can alternatively be expressed in SI units like

v_m = q_m / A_m

     = 4 q_m / (π d_m²)

     = q_m / (a_m b_m)         (2)

where

v_m = air velocity (m/s)

q_m = air flow (m³/s)

A_m = area of duct (m²)

d_m = diameter of duct (m)

a_m = width of duct (m)

b_m = width of duct (m)

Example - Air Flow Velocity in a Duct

The velocity in a rectangular 0.5 m x 0.5 m duct with air flow 1 m³/s can be calculated as

v_m = 1 (m³/s) / (0.5 (m) 0.5 (m))

   = 4 (m/s)

Air Flow Velocity Calculator - SI Units

Air velocity can be calculated with the calculator below. Add air volume - q - and diameter - d - (or length a and b).

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Related Topics

• Ventilation - Systems for ventilation and air handling - air change rates, ducts and pressure drops, charts and diagrams and more

Related Documents

• Air Duct Velocity Diagram - Air flow volume, duct size, velocity and dynamic pressure
• Air Ducts Friction Loss Diagram - Major loss diagram air ducts - SI units
• Air Ducts Friction Loss Diagram - Major loss diagram air ducts - Imperial units ranging 10 - 100 000 cfm
• Air Velocities in Ducts - Recommended maximum air velocities in ventilation ducts
• Air-Duct Sizing - Air flow and required duct area
• Circular Duct Sizes - Dimensions of circular ventilation air ducts
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• Converting Round Duct Diameter to Area - Converting round duct areas to square feet and square meters
• Ductwork Sheet Metal Gauges - Sheet metal gauges used in ductwork
• Equal Friction Method - The equal friction method of sizing ducts is easy and straightforward to use
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• Friction Loss in Ducts - Friction loss or major loss in ducts - equations and online calculator for rectangular and circular ducts - imperial units
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• Recommended Air Velocities in Ducts - Ducts and recommended air velocities
• Sizing Circular Ducts - A rough guide to maximum air volume capacity of circular ducts in comfort, industrial and high speed ventilation systems
• Sizing Ducts - The ductwork of ventilation systems are often sized with either the Velocity, the Constant Pressure Loss (or Equal Friction Loss) - or the Static Pressure Recovery Methods
• Velocities in Ventilation Ducts - Recommended velocities in ventilation ducts