Circular fan-duct for blower for my custom carriage

Circular fan-duct for blower for this carriage http://www.thingiverse.com/thing:1275203. Made for the common 50x50x15 blower by Sunon. The blower is simply fixated by a snap-in fitting. No screws are required.

The benefit of a circular fan is a confined, symmetrical and downward facing air-flow. No dead zones are created. See also this awesome investigation by Desi Quintans http://www.desiquintans.com/coolingtests2. In contrast to the surround duct investigated by Desi the duct presented her