I have used single fan duct to cooling printing material for more than a year.
It shows decent quality in general, but definitely has limit on specific models, which I found cannot be improved with changing design of single fan duct.
This design uses two 40mm fan on both sides.
It can be printed in one piece without support, only tricky point is upper arch of the outlet which I thought might have trouble if you don’t have cooling fan.
I tried to make air blow point just below nozzle area, not too wide.
I cannot say this is perfect but show me best quality so far.
If you have any suggestions, please let me know.