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1.1.1. DIN EN ISO 5801

DIN EN ISO 5801 specifies the procedures for determining the performance of fans of all types. The only exceptions to this are fans used for pure air circulation and so-called jet fans. The following chart shows the symbols and indices valid according to this standard.

Symbol Dimension Unit
A

cross sectional area

 \mathrm{m}^2
A_1 surface at the fan inlet \mathrm{m}^2
A_2 surface at the fan outlet \mathrm{m}^2
b Width of the rectangular area of a pipe \mathrm{m}
c sound velocity at a given point \frac{\mathrm{m}}{\mathrm{s}}
D diameter \mathrm{m}
D_h hydraulic diameter \mathrm{m}
d diameter, e.g. Diameter of an orifice or nozzle \mathrm{m}
h height of the rectangular section of a pipe \mathrm{m}
h_\mathrm{rel} relative humidity -
L length of a pipe \mathrm{m}
Ma Mach number -
Ma_u peripheral number -
n rotational frequency of the fan wheel \frac{\mathrm{U}}{\mathrm{s}}
p absolute pressure  \mathrm{Pa}
p_a atmospheric pressure \mathrm{Pa}
p_\mathrm{d} dynamic pressure \mathrm{Pa}
p_\mathrm{f} fan pressure \mathrm{Pa}
p_\mathrm{fs} static fan pressure  \mathrm{Pa}
p_{\mathrm{sat}(T_\mathrm{dry})} saturation vapor pressure at dry bulb temperature \mathrm{Pa}
p_\mathrm{tot} total pressure \mathrm{Pa}
p_\mathrm{v} water vapor partial pressure \mathrm{Pa}
P performance \mathrm{W}
q_m mass flow \frac{\mathrm{kg}}{\mathrm{s}}
q_V flow rate \frac{\mathrm{m}^3}{\mathrm{s}}
R_\mathrm{dry} specific gas constant for dry air \frac{\mathrm{J}}{\mathrm{kg}\cdot \mathrm{K}}
R_\mathrm{v}

gas constant of water vapor

\bigl(R_\mathrm{v}=461,5 \, \frac{\mathrm{J}}{\mathrm{kg}\cdot \mathrm{K}}\bigr)

 \frac{\mathrm{J}}{\mathrm{kg}\cdot \mathrm{K}}
R_\mathrm{wet} specific gas constant for humid air \frac{\mathrm{J}}{\mathrm{kg}\cdot \mathrm{K}}
T temperature °\mathrm{C}
T_\mathrm{dry} dry bulb temperature °\mathrm{C}
u fan wheel blade tip speed \frac{\mathrm{m}}{\mathrm{s}}
v average air velocity \frac{\mathrm{m}}{\mathrm{s}}
\Delta p differential pressure \mathrm{Pa}
\theta absolute temperature \mathrm{K}
\Lambda friction loss coefficient -
\rho density of the air \frac{\mathrm{kg}}{\mathrm{m}^3}

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