Air Duct Minor Loss Diagram

Overview

Engineering reference data for Air Duct Minor Loss Diagram in fluid mechanics.

Key Formulas

Reynolds Number

$Re = \frac{\rho v D}{\mu}$

Ratio of inertial to viscous forces — determines flow regime.

Bernoulli's Equation

$P + \frac{1}{2}\rho v^2 + \rho g h = \text{const}$

Conservation of energy for steady, inviscid, incompressible flow.

Continuity Equation

$A_1 v_1 = A_2 v_2$

Conservation of mass for incompressible flow.

Darcy-Weisbach

$\Delta P = f \frac{L}{D} \frac{\rho v^2}{2}$

Pressure drop due to friction in a pipe.

Variables

Symbol	Description	Unit
$Re$	Reynolds number	—
$\rho$	Fluid density	kg/m³
$v$	Flow velocity	m/s
$D$	Characteristic dimension	m
$\mu$	Dynamic viscosity	Pa·s
$P$	Pressure	Pa
$f$	Darcy friction factor	—

Minor Loss by Component Type

Minor losses in air duct systems occur at various fittings and components where flow disturbances create additional pressure drops. These losses are proportional to the square of the air velocity and depend on the specific component geometry:

• Bends — Elbows and turns that change flow direction
• Expansions — Duct cross-section increases
• Inlets — Entry points into the duct system
• Outlets — Exit points from the duct system

Bend Angle Correction

For bends with angles other than 90°, the minor loss coefficient can be adjusted using:

$\xi_{\alpha} = \xi_{90} \cdot \frac{\alpha}{90}$

where:

• $\xi_{\alpha}$ = minor loss coefficient for the bend at actual angle $\alpha$
• $\xi_{90}$ = minor loss coefficient for a 90° bend (read from diagram)
• $\alpha$ = actual bend angle in degrees (0° to 180°)

Example: A 45° bend with $\xi_{90} = 1.0$ yields $\xi_{45} = 1.0 \times \frac{45}{90} = 0.5$

Pressure Unit Conversions

References

• Original Source