RE: Using 2 fans in front of each other.
I had to do a lot of research & study on this when I did my V8 motor conversion into the very much smaller engine bay of my S-10 truck.
Same principles of Fluid Dynamics also apply to moving air.
Placing 2 fans - one in front of another - probably ends up blocking airflow & hence lowering the cooling efficiency.
1) For starters the center hub of the second fan & its frame blocks at least in part the flow of the second.
2) Secondly & also unless the two fans' blade rotations were set so that the blades, when rotating, never blocked the airflow space between the other fan's blades - the result would be less than having 1 single fan.
The same principle being used for fighter planes machineguns are set to fire between the blades.
3) There can also be a situation whereby resonant frequencies set up by the RPM differential creates cavitation & no real amount of air gets moved or airflow is decreased.
At a very minimum the fan that is behind the other on the airflow direction side would have to be set at a higher RPM - but the conditions in 1) still limits airflow.
BTW squirrel cage fans are
much more efficient than curved bladed fans.