Fan Formulas and Affinity Laws

In fan engineering, standard air is considered to be air with a density of 0.075 lbm/ft3 when English units are used and 1.2 kg/m3 when SI units are used. Commonly applied industry values for standard air are shown in Table 32-1. For moist air, it is common to assume a humidity of 50% and a temperature of 68°F (527.7°R) in English units and 20°C (293.2°K) in SI units.

Flow rates may be considered on a mass or volumetric basis. On a mass basis, the flow rate is the mass of the

If the fan draws directly from atmosphere:

If the fan discharges directly to atmosphere:

Fig. 32-5 Blade Design for Backward, Radial, and Forward Tips. Source: Buffalo Forge, The Howden Fan Company

Table 32-1 Commonly Applied Industry Values

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