I designed this duct because the "stock" ducts from Guanu, John, and HeathenX wouldn't fit under my platform (custom E3D mount). It was also an exercise in re-learning to draw in CAD after many years of rust. This fan fits the "standard" 10x30 blower fan that SeeMe sells, and fits in the <8.5mm clearance that I have between my effector platform and the tip of the nozzle without risking snagging on a warped part. I also tried to use natural curves to promote laminar flow without turbulence (eyeball method only) and flow as much air as possible without putting unnecessary back pressure on the fan itself.

This mount has 1.5-2mm thick walls, so it's not terribly wasteful to print it at 100% infill. You can experiment for yourself, but that's what I did. Good Luck!

Attribution - Creative Commons

fan, rostock, blower, duct