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Air Ducts - Minor Loss Coefficient Diagrams

Minor loss coefficient diagrams for air ductwork, bends, expansions, inlets and outletsĀ  - SI units.

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Minor loss in air ducts based on a summarized minor loss coefficients and air flow velocity:

minor loss diagram air ductwork

Download and print Air Ducts - Minor Loss Diagram

  • 1 Pa = 1 N/m2 = 1.4504x10-4 lb/in2 = 1x10-5 bar = 4.03x10-3 in water = 0.336x10-3 ft water = 0.1024 mm water = 0.295x10-3 in mercury = 7.55x10-3 mm mercury = 0.1024 kg/m2 = 0.993x10-5 atm

Minor loss for some common duct-work components like bends, expansions, inlets and outlets can be estimated from the diagrams below.

Minor Loss Coefficients - Bends

The minor loss coefficients in 90o bends can be estimated with the diagram below.

air ducts minor loss resistance coefficient in bends

The minor loss in bends 0 - 180o can be estimated with the equation

ξ0-180 = ξ90 α / 90                                            (1)


ξ0-180 = minor loss coefficient for the bend with the actual angle

ξ90 = minor loss coefficient for the 90o bend according the diagram above

α = angle of the actual bend

The minor loss coefficient in a 90o bend like the one below is 1.0.

air ducts minor loss resistance coefficient in 90 bend

Minor Loss Coefficients - Expansions

minor loss coefficients diagram - expansions

Minor Loss Coefficients - Inlets

minor loss air ducts inlets

Minor Loss Coefficients - Outlets

minor loss air ducts outlets

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  • Engineering ToolBox, (2008). Air Ducts - Minor Loss Coefficient Diagrams. [online] Available at: [Accessed Day Mo. Year].

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