fan choice radial or axial 1

[electricpete]

I think I understand the following for pumps:

For high-flow low dp applications we usually use more axial flow pumps, operated at low speed (but still high specific speed).

For low-flow high dp applications we usually use more radial flow pumps, operated at high speed (but still low specific speed).

I read something that seems to imply the opposite for fans. i.e. radial flow fans are used in the high-flow/low-dp applications and axial in the low-flow high dp applications. Why would that be?

 

[insideman]

Fans are the same as pumps: Low specific speed for low flow, high head; High specific speed for high flow, low head. For specific speed in cfm, feet, rpm the changeover occurs at about 2000. Mixflow impellers could be used at Ns circa 200, but it rarely happens.