Page 216 - Chemical process engineering design and economics

Compressors, Pumps, and Turbines 199

Table 5.3 Fan Efficiencies

Fan Type Fan Efficiency 3
TIP, %
Radial" 65-70
Backward inclined
Single Thickness 0 84
Air Foil" 90
Forward Curved 70-75
Axial
Tube" 75-80
Vane 0 85

a) Includes fluid and mechanical
frictional losses
b) Source: Reference 7
c) Source: Reference 8

A final consideration is the fan operating temperature and environmental
conditions. Most axial fans contain the motor, bearings, and drive components
within the duct. Thus, the gases must be noncorrosive, at a low temperature (-34
to 82 °C) (-29.2 to 180 °F) [1], nonflammable and without any particulate matter.
At low or high temperatures, most steels lose their strength [8]. Thompson and
Trickier [8] discuss some elements of duct-system design. Table 5.3 summarizes
efficiencies for approximate sizing of the fans that have been described.

Fan Power

The most frequently used relationship in the design of flow systems is the macro-
scopic mechanical-energy balance. This equation is obtained by integrating the mi-
croscopic mechanical-energy balance over the volume of the system as shown by
Bird et al. [9]. The balance is given by

2
A(v /a) g f 2 dp
———— + — Az+ I —— + W + E = 0 (5.1)
gc Ji P
2g c

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