# Air Duct Components and Minor Loss Coefficients

## Minor loss - pressure or head loss - coefficients for air duct distribution systems components

Minor Loss - Head or Pressure Loss in Air Duct Components - can be expressed with

hminor_loss = ξ v2/ (2 g)                      (1)

where

hminor_loss = minor head loss (m, ft)

v = flow velocity (m/s, ft/s)

g = acceleration of gravity (m/s2, ft/s2)

Minor loss can also be expressed as pressure loss instead of head loss.

Minor loss coefficients for different components in air duct distribution systems:

Component or FittingMinor Loss Coefficient
- ξ -
90o bend, sharp 1.3
90o bend, with vanes 0.7
90o bend, rounded
0.5
90o bend, rounded
0.25
45o bend, sharp 0.5
45o bend, rounded
0.2
45o bend, rounded
0.05
T, flow to branch
(applied to velocity in branch)
0.3
Flow from duct to room 1.0
Flow from room to duct 0.35
Reduction, tapered 0
Enlargement, abrupt
(due to speed before reduction)
(v1= velocity before enlargement and v2 = velocity after enlargement)
(1 - v2 / v1)2
Enlargement, tapered angle < 8o
(due to speed before reduction)
(v1= velocity before enlargement and v2 = velocity after enlargement)
0.15 (1 - v2 / v1)2
Enlargement, tapered angle > 8o
(due to speed before reduction)
(v1= velocity before enlargement and v2 = velocity after enlargement)
(1 - v2 / v1)2
Grilles, 0.7 ratio free area to total surface 3
Grilles, 0.6 ratio free area to total surface 4
Grilles, 0.5 ratio free area to total surface 6
Grilles, 0.4 ratio free area to total surface 10
Grilles, 0.3 ratio free area to total surface 20
Grilles, 0.2 ratio free area to total surface 50

### Example - Minor Loss in a Bend

The minor loss head in a 90o sharp bend with minor loss coefficient 1.3 and air velocity 10 m/s can be calculated as

hminor_loss = (1.3) (10 m/s)2/ (2 (9.81 m/s2))

= 6.6 m

## Related Topics

• Fluid Mechanics - The study of fluids - liquids and gases. Involves velocity, pressure, density and temperature as functions of space and time
• Ventilation - Systems for ventilation and air handling - air change rates, ducts and pressure drops, charts and diagrams and more

## Tag Search

• en: air ducts minor loss fittings components
• es: conductos de aire menores componentes accesorios de pérdida
• de: Luftkanäle geringen Verlust Beschlagteile

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