I've accommodated a 5015 blower fan and a carbon filter within the size of a 120mm fan. I designed this air filtration system with the aim of replacing existing 120mm fans in the enclosure without significantly lowering the temperature.

Being of a universal 120mm size, it should be suitable for various applications. This project is inspired by Nevermore Micro V4.

Notes:

• Please select either the heat-set nut version or the square nut version for the Filter Cartridge.
• Since it is assumed that the 4 corners will be secured with screws, the FrameTop panel is not fixed. Please glue it if necessary.
• The thickness of this is 3mm thinner than the 25.5mm of the 120mm fan, measuring 22.5mm.

Required other than printed parts:

• 1x 5015 blower fan (I recommend double-ball bearing)
• Acid-free Activated carbon pellets
• 2x M3x8mm
• 2x M3x5x4mm heat-set Inserts or 2x M3 square nuts

Print Parts:
Print a total of 5 parts ‘Frame’, 'FrameTop', ‘Filter_Cartridge’, ‘Filter_Cartridge_Lid’ and 'Centering_Jig'.

Pre-assembly preparation:
1.Remove the top cover of the fan and use cutting pliers to cut the bottom cover into a circular shape matching the fan. (Note: the plastic may crack in the direction of the cutting pliers' blade; avoid inserting the blade toward the center to prevent damage to the bearing housing.)

2.Using a centering jig, adhere the fan in the center, while also adhering the wires in a way that does not obstruct the fan's rotation. (Note: I used epoxy adhesive for bonding).

Assembly: 
1. (for heat-set Inserts) Installing M3x5x4mm heat-set Inserts on Filter_Cartridge at 2 points.

1.(for square nuts) Installing M3 square nuts on Filter_Cartridge at 2 points.

2.Place activated carbon pellets into the 'Filter_ Cartridge', cover it with the 'Filter_Cartridge_Lid', and tighten the M3x8mm screw.

3.Set the Filter Cartridge into the Frame, flip it over, and secure the Filter Cartridge to the Frame using M3x8mm screws.

4.Finally, cover with the FrameTop to complete.