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Fan Laws |
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When the working conditions differ from those stated on the
performance curves (speed and diameter); adjustment should be made
using the following formulae before reference to the performance
curves.
In the following formulae index “1” indicates the value on the
curves and index “2” the value to be calculated.
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| Terms: |
| Dynamic pressure |
Pd |
[Pa] = [N/m²] |
| Static pressure |
Ps |
[Pa] |
| Total pressure |
Pt |
[Pa] |
| Air flow |
q |
[m³/s] |
| Air temperature |
t |
[°C] |
| Axial thrust |
F |
[N] = [kgm/s²] |
| Rot. Frequency |
n |
[RPM] |
| Power |
P |
[W] |
| Tip speed |
Vt |
[m/s] |
| Diameter |
d |
[m] |
| Density |
 |
[kg/m³] |
| Efficiency |
 |
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| Rot. Frequency
Conversion |
| Rot. frequency ratio is: |
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Air flow: |
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Pressure: |
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Power: |
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| Diameter
Conversion |
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The difference in diameter should be restricted to 10% above or below the measured diameter, since the fan laws are only accurate for geometrically proportioned impellers.
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| Diameter ratio is: |
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| Air flow: |
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| Pressure: |
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| Power: |
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| Temperature
Conversion |
| Temperature ratio is: |
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T1 |
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| k |
= |
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; where T = t + 273 |
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T2 |
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Air flow is not influenced by temperature.
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| Pressure: |
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| Power: |
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| Other Useful Formulae |
| Total pressure: |
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Dynamic pressure: |
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Tip speed: |
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Axial thrust: |
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Efficiency: |
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