Efficacy of push/pull fan set ups?

MarkS · Aug 1, 2015

I've seen many people recommend push-pull set ups with both air and water cooling. I am about to upgrade my processor and the new one comes with a water cooler and two fans for a push/pull set up. This got me thinking. Both fans turn at the same speed and pull or push the same cfm of air. The fan behind the heatsink/radiator is pushing air through what is effective a closed duct with the fan on the front pulling this same air out. How does this help? Two fans in this set up do not increase airflow. If either fan runs faster than the other, the other fan just spins faster (by the force of the air) to maintain the airflow.

What is the purpose of this?

Alaric · Aug 1, 2015

I would think the exhaust side fan would relieve a fair percentage of the pressure build up from the radiator core due to partial vacuum (low pressure) somewhat alleviating air "stacking up" against the fins from the inlet (high pressure) fan. Easier to push air through=more air through. Or something like that.

Mr.Scott · Aug 1, 2015

MarkS said:
I've seen many people recommend push-pull set ups with both air and water cooling. I am about to upgrade my processor and the new one comes with a water cooler and two fans for a push/pull set up. This got me thinking. Both fans turn at the same speed and pull or push the same cfm of air. The fan behind the heatsink/radiator is pushing air through what is effective a closed duct with the fan on the front pulling this same air out. How does this help? Two fans in this set up do not increase airflow. If either fan runs faster than the other, the other fan just spins faster (by the force of the air) to maintain the airflow.

What is the purpose of this?

Are you really under the impression that CFM does not decrease when you blow it through something?
Even air slows down due to friction.
The second fan pulling helps to regain some of that loss.

NiHaoMike · Aug 1, 2015

It is supposed to make up for pressure drop, but the heatsinks and radiators typically used are not restrictive enough for there to be much of a difference. One good fan will often do better than two cheap fans.

ehume · Aug 1, 2015

When it existed, a lab found that pull fans were best when used with rads. gtg

MarkS · Aug 1, 2015

Mr.Scott said:
Are you really under the impression that CFM does not decrease when you blow it through something?
Even air slows down due to friction.
The second fan pulling helps to regain some of that loss.

I forgot about that! Thanks!

EarthDog · Aug 1, 2015

ehume said:
When it existed, a lab found that pull fans were best when used with rads. gtg

that depends on the rad used i though. We talking about the article from skinee labs?

ehume · Aug 1, 2015

EarthDog said:
that depends on the rad used i though. We talking about the article from skinee labs?

Thank you for remembering the name. I remember their various studies. Pulling through a rad -- I don't remember which one -- produced better cooling by pulling as opposed to pushing. Years ago, though. I don't recall the details.

grumperfish · Aug 1, 2015

I used to do push-pull when I had used the TRUE but with this HR-02 a single fan is fine since it's not at all restrictive. Granted I use a 38mm Sanyo Denki but that's mainly so I can leave it at 7V forever.

NiHaoMike · Aug 1, 2015

ehume said:
Thank you for remembering the name. I remember their various studies. Pulling through a rad -- I don't remember which one -- produced better cooling by pulling as opposed to pushing. Years ago, though. I don't recall the details.

It helps by making use of more of the area. A push fan with a spacer gives nearly the same effect.

Efficacy of push/pull fan set ups?

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