This is a two part cooling system for Mac Minis using 140mm fans. The top and bottom can be stacked together or used separately. In my testing the top fan doesn't dramatically change the temperature of the CPU but dramatically reduces the temperature of the other components such as the SSD.

I was inspired by this https://www.thingiverse.com/thing:3167987. The 140mm fan I used is: Noctua NF-P14s redux-900, Ultra Quiet Silent Fan, 3-Pin, 900 RPM (140mm, Grey) and it is powered by a 3 / 4 pin to USB cable: CRJ Full Speed 12V Voltage Step-Up USB to 3-Pin and 4-Pin PC Fan Sleeved Power Adapter Cable. Both of these are amazon product descriptions.

Direct links: https://www.amazon.com/gp/product/B00KF7NGUE/ https://www.amazon.com/gp/product/B07QFG6LFR/

Note: No idea why thingiverse rotated the pictures. They are the correct way up in on my mac mini.