Fan Configuration Debate

I favor the curved blades, they would have less eddies and cavitation, a more laminar flow than the flat blades. Note the scimitar blades on modern prop planes.

3200 RPM is pretty fast for an inexpensive 8" fan. are you sure the squirrel cage (either configuration) can handle that speed?

Comparing backswept and radial blading.

Some general comments based on fixed tip speed for both designs;

Radial

• Higher input power required
• stress conditions are better (all points on the blade are on a radial line, so can be used at higher speeds).
• Ease of manufacture
• Usually cheaper
• Less efficient
• Develop higher head than back-swept
• Unstable head capacity curve at lower flows (flat in usable range)
• Head curve tends to be steep - drops off fast at high flow.
• Best efficiency is usually close to surge line

Backswept

• Lower input power requirement
• worse stress condition
• lower head than radial
• more expensive construction
• larger stable operating range
• best efficiency is within the safe operating range (away from surge).

In other words, use back swept vanes if the cost is justified.

thanks for the input ,i was hoping that the back-swept type would be better, i was just concerned i may lose some of my pressure[1.25" of Hg.]that the straight blade radial fan produces for me now

marc

You will develop a slightly lower head with backswept as compared to radial vanes. (As stated in previous post). I do not know the shape of the fan casing but if you are using a different geometry impeller in the same casing you may also loose some head.