This is an optimized fan duct that cools both cold end and printed part. The airflow is optimized compared to other models I saw here. Printing can be done without supports. I printed it with a 0.4mm nozzle, PLA and a layer height of 0.2mm and it came out without any problems. Print time with 30% infill is under 1h with my i3 Mini.
I added a version that is 2mm shorter in z direction, for printers with slightly different nozzles. Hopefully that version does not scratch the model.