Minor Loss Coefficients for Air Duct Components

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 as

hminor_loss = ξ v2/ 2 g         (1)

where

hminor_loss = 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 -
90o bend, sharp 1.3
90o bend, with vanes 0.7
90o bend, rounded
radius/diameter duct <1
0.5
90o bend, rounded
radius/diameter duct >1
0.25
45o bend, sharp 0.5
45o bend, rounded
radius/diameter duct <1
0.2
45o bend, rounded
radius/diameter duct >1
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

Related Topics

  • Fluid Mechanics - The study of fluids - liquids and gases. Involves various properties of the fluid, such as 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

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