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The head as a function of air flow volume is in general presented in diagrams as shown below

• The red lines are the pressure head as a function of the air flow volume and the speed of the fan.
• The green lines marked - l - are the throttle lines
• The blue lines are the power consumption of the fan

Pressure and Head

The operation of a fan is often expressed in the terms of pressure

p_t = p_s + p_d = constant         (1)

where

p_t = total pressure (Pa, N/m²)

p_s = static pressure (Pa, N/m²)

p_d = dynamic pressure (Pa, N/m²)

The dynamic pressure can be expressed as

p_d = ρ v² / 2         (2)

where

ρ = density of air (kg/m³)

v = flow velocity (m/s)

Head developed by the fan can be expressed as

dp = p_s2 - p_s1 + (v₂² - v₁²) ρ / 2         (3)

where

subscription ₁ is the inlet of the fan and subscription ₂ is the outlet

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Related Topics

• Ventilation - Systems for ventilation and air handling - air change rates, ducts and pressure drops, charts and diagrams and more

Related Documents

• Fan Inlet - Suction Pressure and Air Density - High suction pressure at the fan inlet decreases the density of air - should be corrected for proper fan selection