Fan Laws
Published 23 Apr 2020
Portable Fans | ATEX & IECEx Certified | Hazardous Area & Explosive Atmospheres
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Article Written By Woodcock & Wilson | 2 of 6 Articles
Woodcock & Wilson are specialist manufacturers of independently certified ATEX fans and IECEx industrial fans for the ventilation of hazardous area locations and potentially explosive atmospheres.
Below is Part 2 in a series of 6 Articles by Woodcock & Wilson discussing fans, the laws, common problems, troubleshooting the main performance issues and getting your fan started again if you encounter any issues.
The fans are used to determine theoretical performance data for varying combinations of impeller speed, diameter and air densities.
Here we will only consider the relationship and effect of speed on volume, pressure and power for a constant impeller diameter handling air at a constant density.
When speed is varied on the same size, handling constant density air (e.g. fan used with frequency inverter drive).
Fan Laws Further Explained
Flow Rate varies directly as the speed.
Q2 m³/s = (rpm2/rpm1) x Q1 m³/s
Pressure varies as the square of the speed.
P2 Pa = (rpm2/rpm1)² x P1 Pa
Power varies as the cube of speed.
Power2 kW= (rpm2/rpm1)³ x Power1 kW
Performance Curve Showing Speed Variation
Maximum speed : 1480 RPM.
Reduced speeds :
• 1110 RPM (75%)
• 740 RPM (50%)
Performance Curve Showing Speed Variation
Here we will only consider the relationship and effect of fan diameter on volume, pressure and power for a constant impeller speed handling air at a constant density:
Flow Rate varies as the cube of the diameter.
Q2 m³/s = (D2/D1)³ x Q1 m³/s
Pressure varies as the square of the diameter.
P2 Pa = (D2/D1)² x P1 Pa
Power varies as the fifth power of the diameter.
Power2 kW= (rpm2/rpm1)5 x Power1 kW
Pressure and Power vary directly proportional to gas density, combining speed, diameter and density we have the following :-
Q2 = Q1 x (n2/n1) x (D2/D1)³
P2 = P1 x (n2/n1)² x (D2/D1)² x (ρ2/ ρ1)
W2 = W1 x (n2/n1)³ x (D2/D1)5 x (ρ2/ ρ1)
Where:
Q = flow rate
P = pressure (total, static, or dynamic)
ρ = gas density
n = fan rotational speed
D = impeller diameter
W = impeller power
See further information about the Exstream range of Portable ATEX Certified Fans
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