Question about Push-Pull

[HESmelaugh]

I'm wondering what might happen if you are using fans in a push-pull configuration on a radiator and the fan's CFM don't match exactly. I've noticed that sometimes one fan can need a bit more or a bit less voltage to reach the same RPM as another fan of the same type.

What effect would it have if I was using two fans in push-pull and had the connected via a split-cable. They'd both be getting the same voltages but let's say they are quite a bit off on RPM. Would this be a problem?

[dsumanik]

Id say put the faster fan on the push, that way it will help compensate for the spin on the slower fan somewhat to match the speeds a bit better (your pull fan always spins a bit faster then the push, even with matched fans).

I don't think this will hurt anything but depending on where the RPM's are lining up, probably be noisy

[Capt Proton]

I don't see this as a problem. I am not an aerodynamics expert, I am simply using my own logic. First fan speeds up the air and pushes it into the rad, which slows it down again somewhat. Second fan grabs that air and speeds it up some more and expels it. All the second fan is doing is helping overcome the pressure built up by the air striking the radiator fins. Molecules thin out somewhat (same as air flow over an aircraft wing), but more of them are involved.

[WhiteFireDragon]

depending on your setup, it could hurt or help performance. i think if you have fans that are quite different in cfm and rpm, then the weaker fan actually blocks airflow as compared to free flowing air if the weaker fan was not there. on the other hand, if the difference in cfm is rather small, then the second fan helps moves the air and adds a little more air pressure.

i had this same question a while back, and Vapor did a test on this. let me try to find that post or thread.

EDIT: here's the thread, and vapor's results are on the bottom
http://www.xtremesystems.org/forums/showthread.php?t=189402

[Jah]

A guesstimate would be that as long as the flow with the more powerful fans are not exceeding the free air flow on the weaker fans you should see a performance increase. The pressure that the push fan needs to produce for a given flow is reduced by the pull fan.

I can't see how using the same fan and just dealing with sample variation could effect performance noticeably.

[HESmelaugh]

Thanks for the replies and the link. :up: