This is my second 3D OpenScad design, so please be kind. This is a modified version of the hot end fan by Johann Rocholl. The Mini Kossel master zip file can be found at https://github.com/jcrocholl/kossel
It has been specifically sized for a J-Head hot end.
It is also based on my 30mm version, but I found that the 30mm fan I bought was very noisy. Could have been because it was cheap.
I enlarged to a 40mm fan with a duct to blow cool air across the printing part. I have uploaded to OpenScad design file in the hopes that someone can improve on it. I am pretty sure you could mirror the 40mm fan part and have two 40mm fans blowing.
You will need two 40mm fans to fully appreciate the cooling. M3 screws are used to hold the fans in place. The 40mm fan is on all the time and in my setup is connected to the 12V Aux connection of the RAMPS board. The ducted 40mm fan is connected to D9 to provide cooling to the part.