I freaking love this cooler by @Hangtight, but it isn't compatible with a 4020 fan and I crave the best of both worlds. So, I made a fan duct which solves this problem.(Edit: the newest version of Hangtight's cooler isn't compatible with this fan duct. But this one is. There is now also a modified fan duct based on this available in Hangtights files.)
Fan ducts are a great way of removing the center of the fan where no air is flowing from the equation as well, providing something much closer to the simulations @Hangtight is doing to test his cooler design.
Bit of a tricky print. Print slow (60% of normal print speed, or so) and with Lift Head setting on with Minimum Layer Time set to at least 15s in Cura. You'll probably want to support the overhang on front of the upper mounting plate, but don't support the interior of the duct. You may find a brim is needed if you're having trouble with bed adhesion.
You'll need some M3x6mm screws (or thereabouts) and matching nuts to attach the fan to the shroud.
You may also like my other related listings:
Velocity stack, 5015 blower fan
Velocity stack, 40mm