Do you want your part cooling fan to blow the debris off your print bed? Or do you want a strong, flow from at least 2 sides? Do you have a Imagine That Titian/Atlas, Creality CR-10, or Afinibot A31? Well friend, I've got the set-up for you! I didn't use no new fangled CFD programs or nuthin, but I meditated and tried to think like air. Then I over did it. That's even better.
Download the extruder cooling duct here:
It is nice and compact and raises up the fan away from the heat block.
2 - 50mmx15mm blowers
2 - M3x20mm socket head bolts (attach the blowers to the bracket/duct)
2 - M3x10mm socket head bolts (attach the bracket to the extruder carrier)
2 - M3 nuts (attach the blowers to the bracket/duct)
Make sure to use a higher temp filament. Scaled for PLA/PETG. Scale up around 2% for ABS. I used Essentium Engineering Grade PLA.
I only had a narrow wall of supports in the middle of the ducts, just a little way in. That way I could still get a pair of needle nose in there to remove them easily.
I printed withe the back, flat part on the bed.
I printed the extruder duct as oriented on the machine, so upright, with the flat down.