where
Δpminor_loss = minor pressure loss (Pa (N/m2), psf (lb/ft2))
ρ = density of air (1.2 kg/m3, 2.336 10-3 slugs/ft3)
v = flow velocity (m/s, ft/s)
Minor loss coefficients for different components 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 |
Download and print Air Flow - Minor Loss chart
The minor loss in a 90o sharp bend with minor loss coefficient 1.3 and air velocity 10 m/s can be calculated as
Δpminor_loss = (1.3) (1.2 kg/m3) (10 m/s)2 / 2
= 78 (N/m2, Pa)
The study of fluids - liquids and gases. Involving velocity, pressure, density and temperature as functions of space and time.
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Minor loss coefficient diagrams for air ductwork, bends, expansions, inlets and outletsĀ - SI units.
Required duct area vs. air flow.
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The equal friction method for sizing air ducts is easy and straightforward to use.
Ductwork air leakage classes.
Minor pressure and head loss in pipes vs. equivalent length in tubes and duct systems.
Minor loss coefficients for components used in pipe and tube systems.
Pressure loss in ventilation system components like dampers, filters, heaters, coolers and more.
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