What fan can I use in a close loop application with a backpressure

[vapl153]

I have a test application that required a high velocity (subsonic) air trough a restriction in a close loop system. I would like to know wich circulating fan would be suitable (axial, centrifugal, mixed flow, turbo) since the fan will have a backpressure from the close loop arrangement.

Design parameter:
6in max pipe in a close loop (fan, restriction, elbow 180deg, intercooler, elbow 180deg, back to fan)
Medium: air at 110F and 85%RH
800 - 1200 scfm
12 psig max pressure
Restriction 2.25 in
Intercooler full pipe size after the restriction

I was thinking of a mixed flow fan used in commercial airplane for the size and capacity and pressure or a turbo arrangement where the return after the restriction would turn the exaust inducer, and the outlet to the intercooler than back to the other side of the turbo (there will be a motor connected to the turbo)

Thanks if you can guide me on this one

[FredGarvin]

Just out of curiosity, why the closed loop arrangement?

[vapl153]

The close loop arrangement is for:
- Keep the same gas isolated and eventualy pressurise the system
- Increase the velocity of the air using only one fan, the air comes back to its inlet
- Decrease the fan Amperage once the flow gets going (mixed flow fan are at 3300 W)
- Be able to control the gas temperature with intercooler

Its similar to a small Wind Tunnel
http://sln.fi.edu/flight/first/tunnelparts/tunnel_loop.html

My application require a high velocity small fan, thats the problem,
Reason: Further test will be made under pressure and big size SS pipes are expensive, I have to limit it to 6" dia pipes