Minor Loss Coefficients for Air Duct Components

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

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

h_{minor_loss} = ξ v²/ 2 g (1)

where

h_{minor_l}_oss = minor head loss (m, ft)

ξ = minor loss coefficient

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 common in air duct distribution systems:

Component or Fitting	Minor Loss Coefficient ξ
90^o bend, sharp	1.3
90^o bend, with vanes	0.7
90^o bend, rounded radius/diameter duct <1	0.5
90^o bend, rounded radius/diameter duct >1	0.25
45^o bend, sharp	0.5
45^o bend, rounded radius/diameter duct <1	0.2
45^o bend, rounded radius/diameter duct >1	0.05
T, flow to branch (applied to velocity in branch)	0.3
Exit to room	1.0
Entry from room	0.5
Reduction, abrupt (due to speed after reduction) (v₁= velocity before reduction and v₂ = velocity after reduction)	0.5 - (v₁ / v₂)²
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 < 8^o (due to speed before reduction) (v₁= velocity before enlargement and v₂ = velocity after enlargement)	0.15 (1 - v₂ / v₁)²
Enlargement, tapered angle > 8^o (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

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