Microswiss Flowtech Fan Duct – Kobra S1

The Microswiss Flowtech hotend has unlocked new speed capabilities for the Kobra S1, with users reporting flow rates of up to 55 mm³/s.

Unfortunately, the new hotend is 1.2 mm longer than the stock unit, which renders the stock ducting unusable, as it blows air directly onto the silicone sock instead of the nozzle. Additionally, the stock ducting was never designed for such high speeds.

Here's a full video for this fan duct along with the Flowtech hotend and the Magnum v2.1 printhead cover completing a good quality benchy in under 10 minutes.

Update:

1. I Uploaded a newer model that adds a hole and cable routing for a 24V LED used to light the toolpath.
2. ABS+_24VLED_V2HE is a High efficiency version with the integrated 24V LED mod. This one is still being tested but it should outperform the original. The math and explanation is below.

Notes:

• This is an early version of a replacement duct designed to address this specific issue with the Flowtech hotend. It may not work with the stock hotend or other aftermarket options.
• This is a work in progress and was released quickly because many users are struggling to achieve consistent cooling with the stock duct. Expect issues with this early version.
• CFD simulation link: https://www.simscale.com/projects/b3b3scat/kobra_s1_plenum_flowtech_duct_331324124/
• I have only test-fitted this duct with the front cover I designed. I recommend giving that cover a try as well. Please report any issues when using the stock cover or any community-designed alternatives.
• Print in ABS at minimum to withstand high temperatures. PETG WILL DEFORM!
• I do not believe this duct will provide adequate cooling at the extreme flow rates this hotend is capable of. However, it should perform better than the stock duct and serves as a good starting point. A CPAP system or a second auxiliary fan may ultimately be the best solution.
• I am currently working on print profiles for the Flowtech hotend and will upload them soon.

This section explains the math behind the HE version. The nozzle outlets are further optimized according to the Stock fan P-Q Curve provided by manufacturer [https://www.coolcox.com/uploads/BF5020a%E6%9B%B2%E7%BA%BF%E5%9B%BE.jpg]. Optimizing for Peak efficiency means the fan converts its 5,000 RPM rotational energy at 100% fan speed into the maximum possible combination of air velocity and mass flow,

The mathematical peak power sweet spot occurs exactly at 3.6 CFM and 7.0 mmH₂O.

Q = 3.6 CFM ≈ 1.699×10−3 m3/s
P = 7 mmH₂O ≈ 68.65 Pa
Where Air density ρ = 1.204 kg/m³

Using the dynamic pressure equation:
P=1/2ρv^2

We get an air velocity of ≈ 10.68 m/s

And knowing that Q=v/A
Gives us an ideal Area of A` = 159.08 mm2.

We then factor the Coefficient of drag for the printed ABS duct (Assume Cd = 0.90)

That gives us A = A` / 0.9 = 176.76 mm2.