The rise of the axial flow fan
When reading the previous sections of this Chapter, it will have been noted that the years since World War 11 have been characterized by the rapid development of axial flow fans. This has been due in no small part to the efforts of Woods of Colchester Ltd — now part of the global Flakt Woods Group. No other industrialised country manufactures such a high proportion of axial flow fans (well over 50% of the total). A brief history of this company therefore seems appropriate.
In 1947 the first standardized range of axial flow fans were introduced, these having sand cast constant chord, constant pitch aluminium impellers. It is believed that this range was the first to be manufactured on a batch production basis.(See Figure 1.57.)
Figure 1.57 First batch production of axial flow fans
By 1958, contra-rotating two stage axial flow fans were introduced, using many of the same components but with the second stage having opposite handed blades). By this means, the rotational energy of the air from the first stage was recovered. Instead of twice the pressure being developed, this was increased to three times. Many applications previously furnished with centrifugal fans could now be provided with these units which were more compact, cheaper and had a reduced starting load on the supply.
The performance of an aeroplane propeller can be changed by rotating the blades, such that their pitch angle is altered. In 1963 this technology was adapted by Woods, in its first range of Variable Pitch in Motion fans.
Posted in Fans Ventilation A Practical Guide