ANYCUBIC KOBRA X | Anti-clog Bellmouth Hotend Cooling Fan Intake [ CFD Tested ] Guaranteed Results !

ANYCUBIC KOBRA X | Anti-Clog Super-Silent Bellmouth Intake

[ CFD Tested | $1.6x Velocity Stack at Max RPM ]

3D Printer Mods Series

Published by 3D Print Official

Inspired by:

Vena Contracta

—and non-dry Filament.

Problem with "Choked" Intakes

Standard flat fan intakes suffer from a physics phenomenon known as Vena Contracta. As air rushes into a sharp-edged orifice, streamlines converge and "pinch" the flow, creating a high-velocity, low-pressure "contracted vein" that is smaller than the actual opening. This creates massive turbulence, starves the fan blades of air, and leads to:

• Heat Creep & Nozzle Clogs: Inconsistent cooling in the transition zone.
• TPU Failures: Excess heat softening the filament before it reaches the melt zone.
• High-Pitch Noise: Turbulent air "tripping" over sharp plastic edges.

The Solution is Geometric Optimization

This bellmouth is engineered with a 45∘ tapered curve to guide air smoothly from a low-velocity intake to a high-velocity duct. This eliminates the Vena Contracta effect, allowing the fan to utilize its full blade area.

• Performance Gain: Average improvement of 37.44% across all metrics.
• Stringing Reduction: Up to 80% improvement even with non-dry PLA.
• Silent Operation: Drastic reduction in idle noise by smoothing intake airflow.

Sizing & Tolerance (33 Versions)

Every printer and material (PLA, PETG, ABS) has different shrinkage and expansion properties. To ensure a perfect, airtight press-fit on the 25.5mm Kobra X fan opening, I have provided 33 different versions in 0.05mm increments.

• Recommended Starting Size: 25.75mm or 25.80mm.
• Requirement: The fit must be firm enough to withstand vibration compensation tests.
• Important: Ensure the fan blades spin freely and do not rub against the bellmouth neck.

The "Crucial" Step: Post-Processing

Shape alone is not enough. To achieve the CFD-verified results, the surface must be smooth.

1. Sanding: Use 120 grit, followed by 320 grit followed by a wet sanding procedure, sanding in the axial direction (along the airflow path).
2. Chemical Smoothing: For ABS prints, an acetone vapor bath is highly recommended.
3. Refinement: Smooth all sharp edges, especially at the inner neck hole, to remove any micro-turbulence at the point of maximum velocity.

Print Settings (Optimized 3MF Included)

• Layer Height: $0.08mm (for maximum geometric accuracy).
• Material Weight: ~4 grams (Minimal extrudder mass impact; zero ghosting issues).
• Print Time: ~30 minutes.
• Supports: Optimized for easy removal within the provided 3MF file.

Note:When you find your optimal dimensions for your specific material, please share them in the comments along with your finishing procedure to help the next users find the correct size faster!

Stop fighting physics and start using it: Print the Kobra X Bellmouth, silence the turbulence, and hear the difference for yourself.

https://www.youtube.com/watch?v=HMOnJA_I21s

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Research and CFD Analysis by 3DPrintOfficial