Fan Capacity Diagrams
Pressure, head, air flow volume and fan capacity diagrams.
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Pressure head as function of air flow volume may be expressed in a diagram like the one below:
- red lines are pressure heads as function of air volume flow and speed of the fan
- green lines marked - l - are throttle lines
- blue lines are power consumption
Pressure and Head
Operation of fans are often expressed in terms of pressure
pt = ps + pd = constant (1)
where
pt = total pressure (Pa, N/m2)
ps = static pressure (Pa, N/m2)
pd = dynamic pressure (Pa, N/m2)
Dynamic pressure can be expressed as
pd = ρ v2 / 2 (2)
where
ρ = density of air (kg/m3)
v = flow velocity (m/s)
Head developed can be expressed as
dp = ps2 - ps1 + (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
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Ventilation
Systems for ventilation and air handling - air change rates, ducts and pressure drops, charts and diagrams and more.
Related Documents
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Fan Affinity Laws
The affinity laws can be used to calculate resulting volume capacity, head or power consumption when speed or wheel diameters are changed. -
Fan Inlets - Air Density vs. Suction Pressure
High suction pressure at a fan inlet decreases the density of air - and should be corrected for proper selection of the fan. -
Fans - Capacity Control
How to modulate fans and their capacities. -
Fans - Efficiency and Power Consumption
Power consumption and typical efficiencies of fans -
Fans - Volume Flow, Pressure Head and Power Consumption vs. Air Temperature and Density
The temperature and density of the air influences on the volume flow, pressure head and power consumption in a fan. -
Types of Fans
Axial and propeller fans, centrifugal (radial) fans, mixed flow fans and cross flow fans. -
Types of Fans - Capacity Ranges
Centrifugal, axial and propeller fans and their capacity ranges.
