Kelly,

 

I ran some numbers through the spreadsheet I created.  This assumes that we need to maintain a 20cfm flowrate.  I got the data and equations off the net.  Do a google search with "flow resistance weldbend". The first link takes you to a page that explains 'bend equivalence' and the next page (link at bottom) explains how to calculate flow rates and Questions for the list.

 

  How does the cooling performance drop as the flowrate goes down?

  Is 20cfm the very minimum flow necessary to provide adequate cooling?

 

Maybe better check your flow rate units; gpm vs cfm.  20 cfm is way too high.  For a 2-rotor you’d probably need a max of around 25 gpm, which is about 3.5 cfm.

 

Al