Fans

one of these silly questions, just been thinking, for example if you run a computer fan at a set speed and moves 200cfm, if you bolt a second identical fan to the first, assuming there are no leaks between the housings and, run them both at the same speed and same direction would you move more air, less air or the same amount, would a airgap between the two fans have any effect on the results ????
Ian:)

I suppose in theory it should produce twice the "pressure" but the same amount of air . Just like the multi stage compressors we use to pump up the Scuba bottles (3000 + PSI ) Why was you thinking of using a couple for a "hidden" supercharger ? Yes its all been tried as a lot are 12v !!!

Can answer this one from experience , you move more air as you have less pumping losses , would think it will be about 15 to 20 % increase

Sorry, More mundane than that, Heater fan, trying to get more air thru a limited CSA, doubling up could be a soloution, wonder what would happen if they were physically linked together with a common shaft?

You'd be much better to run them in opposite directions because the second fan (the one downstream) will be rotating in the same direction as the air which the first fan has just worked. Thus the second fan will be much less efficient than the first. If you run two fans in opposite directions the second fan will be doing the most work as it'll be rotating in the opposite direction to the air coming towards it.

However, it depends on how whether it's possible to do that or not.