CPAP Tube diameter impact on performance

I run some CFD simulations to have a rough idea of how much the diameter of the CPAP tube has an impact on the cooling performance. I tried to model 19mm OD vs 18mm OD tubes, so approximately 18mm ID vs 14mm ID, and I chose the worst case possible, to have an idea of the maximum impact. I used a longer tube than even a 350mm printer would, with tighter bends and very deep and angular cuts to represent the corrugated nature of the tubes we use, and used the pressure/flow curve of a Wonsmart WS7040-24-V200.

According to the formulas for the pressure losses in a straight rough tube the 14mm ID tube should have a drop of 1900Pa, while the 18mm ID one only 860Pa, a difference of 1040Pa. In the simulations the actual drops are approximately 2800Pa and 1700Pa, a relative difference of 1100Pa, in line with the theory. The higher total values are due to the concentrated losses in the bends and in the ducts.

This resulted in a 20% reduction in flow rate and average speed at the outlets, which is significant, but represent the absolute maximum possible difference that would never appear in the real world. In the real world shorter tubes, grooves in the bends, and much more restrictive ducts would lead to much closer results.

The key takeaway is that bigger tubes are better for performance, but they have a weight and rigidity penalty, increasing the toolhead vibrations, and there aren't yet 19mm HT tubes, so 15mm is a good compromise for all around quality of life. Following this principle the monolith toolhead is designed with a 15mm tube in mind, but it can easily be used with a 19mm tube with an adapter if one so desires.