Cooling talks - Flow Rate vs Air Speed

When choosing a toolhead, you also choose a part cooling fan with it. There are multiple possibilities, but it all comes down to the "flow rate vs air speed" argument.

The two main performance choices are thick axial fans (3628, 4056, etc...) or radial compressors, commonly referred to as CPAP (7040, 9290, etc...).

• Axials are great at moving a lot of air, but they lack the static pressure to accelerate the air to high speed and can't be focused directly at the nozzle. This makes them great for cooling big plates, where the toolhead constantly moves around and doesn't sit in one place, letting the air cooling everything uniformly. Unfortunately the low air speed means that for short layer times, like for example the benchy chimney, the air doesn't get close enough to the nozzle and the part, affecting cooling significantly.
• CPAP fans have tons of pressure and a lot more flow rate than the usual blower fans (4010, 5015, etc...) but a bit less than a pair of thick axials. This means that with suitable ducts they accelerate the air to extremely high speed, perfect to focus on the nozzle to cool the plastic as soon as it is extruded. That's ideal for small details, but for big parts where there are long lines the nozzle stays near the extruded plastic for a short time, limiting the cooling potential.

What should I choose? CPAP usually win, because their limitation can be worked around with suitable ducts geometry, while axials will always struggle for printing small batches or single parts.

We selected CPAP for the Monolith toolhead, as we feel like it's the highest performing and most balanced option, and we plan to make the best out of it by simulating and testing innovative ducts, that will come out later once refined.