How can we control the airflow in a fan which can be 3D printed?
Look at your fan: it spins in one direction, and the blades push the air from one air to the other side. In fact, the fan is nothing but a propeller! There are ways to optimize them. The Rotation goes for example clockwise, the leading edge grabs the air and the trailing edge releases it on the other side, and if the leading edge is towards you, then the air is pushed away. In the simplest way, it would suffice to physically flip the fan around.
A 3D printed new fan would need to have the whole geometry of the fan blades &quot;flipped&quot; (mirrored around a non-rotational axis). Now the leading edge of the fan is away from you, the trailing edge on your side, the airstream is again from the leading to the trailing edge, and the air comes out on your side.
cave!
Not all fans can be made to reverse the airflow by flipping the fan geometry: Radial fans just because less efficient.
Other fans can be made spinning backwards by swapping the polarity, but others use a simple diode setup and always spin their way. Also note that fans spinning backwards often suffer from reduced efficiency, as the blade geometry is optimized for one direction of spinning.