Chain-Ganging fans

Suppose you're limited in space to make air passages. What happens if you put 2 fans inline (in a tube perhaps) one of them after the other?

Is the second fan going to turn faster than it would in open air? Can it actually turn faster, electrically? Only up to a certain point? Or would it just reduce the power draw on the 2nd fans circuit?

I'm guessing this is less airflow than the two fans having separate intakes - true do you think?

Suppose you had a header where the two fans shared an intake without being inline?

matt theWesson

I tried this in my shuttle case. Basically, it just makes more noise. It didn't seem to add much cooling. The problem is the fans are designed to pull on air that isn't otherwise moving. If the air is moving because of the the first fan, the second will hardly do anything at all. Yes, the fans will run faster than normal and also draw less power each, but you still won't get much more airflow than having one fan.

A considerably different case is when you have something to slow down the air between the fans. Radiators, heatsinks or just a large volume placed between the fans will help them run more effeciently. Of course, this is only if you need to cool these things.

Basically, running two fans increases pressure, but not airflow. The closer they are to each other, the more noise and turbulence they'll create. Unless there's something (like a radiator) between the two fans, there's really no point.

TheWesson said:

Suppose you had a header where the two fans shared an intake without being inline?

matt theWesson

Click to expand...

I think that might work better, I was talking about here

http://forum.oc-forums.com/vb/showthread.php?s=&threadid=246214

this might be an interesting experiment
hook both fans to seperate fan controllers and have 'em in the tube as said above but you'll have to vary the rpm of each fan due to the fact that the load on each fan will vary
if the fan at the exhaust end is spinning, it should actually produce less pressure for the fan on the intake side, so then it should be able to produce the same amount of work with less effort but if it's spinning wouldn't its moving air help the exhaust fans spin, so then the exhaust fan would be able to produce its workload with less effort too...right.. hmm, I think I'm confusing myself now...
anyway, it seems like the fans should be able to produce the original amount of airflow but with less effort

You won't increase CFM's... well, actually, you kinda will, but in a roundabout way. Multiple fans in series will increase the pressure, and if it's blowing through a rather restrictive heatsink, it could increase the cfm and performance.
Sadly, you will increase the noise level massively... fans are meant to cut through still air. If the air is turbulent and moving when it hits the second fan, it will increase the noise level output.

This has been tried many times over the years without any improvement, except when one fan is blowing in cooler air from outside the case.

But “two fans sharing an intake without being inline" has not been tried as far as I know.