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Louvre Head Loss

Pressure drop across angled louvers (blinds) in a duct.

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Every K = 1 component costs one velocity head — about 60 Pa at 10 m/s in air — and fan power rises with the cube of the flow you push through it.

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Figures assume typical conditions and the stated method. For measured, guaranteed numbers on your plant, our engineers run site surveys, heat loss audits, and full process models.

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Louvre Head Loss

Calculates the pressure-drop loss coefficient and pressure drop across angled louvers (blinds) fitted inside a duct or pipe.

Reynolds Number

Re=νVDh

where V is the mean flow velocity, Dh is the hydraulic diameter of the duct, and ν is the kinematic viscosity of air. For a square-section duct, Dh equals the side width.

Loss Coefficient

The loss coefficient has two parts — a geometric base term and a Reynolds-number-dependent turbulence correction:

K=K0+max(0,1Re50)kqu

When Re ≤ 50 the turbulence correction term is taken as zero (the factor is clamped).

The geometric base term is:

K0=(FAR1FAR)2

The angle-and-count coefficient kqu increases with louver angle θ and number of louvers n:

kqu=C(n)sin2θ

Pressure Drop

Δp=K21ρV2

References

  • Idel'chik, I.E. and Fried, E., Flow Resistance, a Design Guide for Engineers, Taylor & Francis, Washington D.C., 1989, p. 306.
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Frequently asked questions

Pressure drop across angled louvers (blinds) in a duct. Enter your inputs and press Calculate — the worked solution shows every step of the method with your numbers substituted in.

K expresses a component's pressure drop in velocity heads: Δp = K·½ρV². A K of 1 means the component destroys exactly the kinetic energy of the approaching flow. It is dimensionless, so the same K applies at any flow rate — the pressure drop then scales with velocity squared.

Compute each component's Δp at its local velocity and add them, together with straight-duct friction. Where the duct area is constant you can equivalently sum the K values first. The result is the static pressure the fan must develop at that flow rate.