Experimenting around with the effect of internal fins to direct the air flow from a 40mm fan. Thinking is that it will reduce the swirling air from the fan that causes the air flow rapidly spread out. Perhaps for a more laminar flow.

It made a huge difference, it dramatically narrowed the cone of air with no noticeable air flow reduction.

To visualize the effect i directed the air flow over a wet towel and took a thermal photo, any place with an air flow cools below ambient. You can see a considerable change though the test does not do it justice as i think some reflected air hitting the towel spreads out to make it look wider then it is.

Adding internal fins to air duct cooling nozzles might help with flow, more testing needed.