My current view on ducts! This may not be reality, but it's my reality at this point!

I have made so many ducts and had so many failures! Without CFD software I would still be cussing!

My knowledge of the ducts/airflow is very limited. Design, test, repeat. Through some of those changes I learned some, and some nothing. I am an expert is what not to do!
Until I started to CFD analyze them the results were not great and I am sure there is much more to improve. It is what it is! Hope to see more ideas out there!

I have tried water tests (I have some videos also of water depression tests), and they are lacking! What seems great in water does not always translate to a good duct. Although it will show some things, but it is not a tell all, at least in my experiments!

The main take from this is to show that cooling at the nozzle may seem the obvious thing to do. However, if you are moving along at a good pace, the toolhead is not there long enough to do much cooling. Also, hitting the material, hard, with air, can cool sections too fast and lead to warping, cracking, ETC. In my last video of the 11 minute benchy you can see discoloration of the filament. Even though I was printing at 290C, the 4028 and duct was cooling too much. Not so much the layer adhesion was bad, there was no cracking of the part and was quite strong, but enough there was a dull finish in certain areas. The filament, as is, is almost a matte finish anyway, but clearly a different color in different portions of the model. This is actually a good thing, in terms of fan efficiency. I can better control the part with fan instead of the temp of the hotend. This means I need to better slice the file keeping in mind where to put the air or where to slow down or speed up the print.

Thanks for watching.