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Push vs Pull question.

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[IO]ERROR

Limp Gawd
Joined
Jun 26, 2006
Messages
160
Out of these two which is the better way to go or does it not matter. I'd rather keep the rad against the case wall for looks purposes (no need for a fan grill) but I'm not looked into it. I would think it wouldn't make a difference but I figured it couldn't hurt to ask.

Case Wall --> Fan --> Rad
Case Wall --> Rad --> Fan
 
Do what your car does and pull air through the rad. Its doesnt make much a difference anyhow.
 
From a cooling standpoint I'm pretty sure it's been proven that the performance difference is negligible, however I believe pulling air through the radiator is quieter.
 
Pull might be better. For low flow fans, it probably doesn't really make much of a difference. There is only a difference between push and pull performance if the fan's exhaust is flowing fast enough that the momentum of the stream is significant when compared to pressure gradients (This requires a very high airflow speed.) That probably sounds confusing, but it can be understood fairly simply.

On the suction side of the fan, there is simply a pressure gradient. Speaking loosely, suction doesn't have momentum.

On the exhaust side, the airflow is being expelled with directed momentum. If that flow is impeded (especially near the fan, like a radiator with very little clearance), the flow can get slowed down by the resulting backpressure. The further that the flow can move unimpeded after the fan, the more the momentum diffuses, and the less significant this effect becomes.

Of course, there is also a baseline amount of backpressure generated by the obstruction of the radiator itself which is the same whether it's in push or pull. But there may be an extra (uaually very small) backpressure in push configuration due to the disruption of the exhausted flow's momentum.

Moral of the story:
1. Pull is not worse than push.
2. Unless you're overvolting Deltas, you probably shouldn't care about any difference anyways. Usually the push/pull choice is settled by aesthetic or case layout concerns anyways.

P.S. These comparisons all assume you've got a sealed flow between the rad and any fans. If you're not taping/shrouding properly, this whole discussion is mostly moot.
 
Thanks for the info. I'll be using two Yate Loon D12SL-12 120mm fans with a custom shroud.

With the setup I am planning I'm glad to know I can have the red against the case with little or no ill effects.
 
Fans should pull because the airflow up to the fan is direct, and turbulent afterwards. Turbulent air doesn't flow very well. Yes, a properly spaced shroud helps, but pull will still be better.

Fans create a pressure differential across the radiator. Barring turbulence, the difference in the pressure differentials of push/pull is negligent, and will result in the same airflow. Barring turbulence, the same airflow through the rad will result in the same velocity. The mass of the air is fairly constant. Momentum = mass x velocity.

Yes, feeling the airflow of a fan on it's own gives you the impression that it'll push harder. A lone fan with no restrictions will pull from a much wider area than the relatively directed exhaust, which makes it seem like the exhaust is more powerful. The same amount of air is being flowed (hello Law of Conservation of Mass) through the intake as the exhaust, it's just tougher to feel the intake side when the fan is unrestricted. If you restrict the suction area, for example placing the fan in the center of a tube with the same diameter as the fan, there's just as much velocity entering as exiting. In the case of the tube, you'll still feel a bit more on your hand if you put it near the opening, but that's because the nerves in your hand feel the back-pressure more than they would feel the suction.

For some reason, I can't find the push vs pull testing article right now (but here's one for push/pull), but it's always been accepted here that pull is better than push due to turbulence.

But do what you want. If it fits better in your case one way rather than another, then go with that. Keep in mind that you don't have to exhaust air out the back through the rad, you can bring it in through the rad at the back and swap some other fans around in your case instead. ;)
 
RickyJ said:
Keep in mind that you don't have to exhaust air out the back through the rad, you can bring it in through the rad at the back and swap some other fans around in your case instead. ;)
Click to expand...

This is my plan. Dual 120mm Yates pulling air in through the rad and a single 120mm scythe flex fan exhausting it.
 
That should be just about perfect. I've rearranged my rad and fans many times, finally got it good now with fans at the top of my case sucking case air through the rad. As long as everything is set up properly, doesn't matter how you route the airflow in your case.
 
PULLING is typically better, given that the fan/radiator interface is sealed well. Especially with slower speed fans.
 
hot_fifty said:
by pulling you mean - rad->fan->casewall right...
Click to expand...

The mounting arragnement isn't what push/pull is about. It refers to whether the fan is pushing air through the rad or pulling it. (If your arrows refer to the direction of airflow then yes, that's pull. But it is more commonly set up like this: casewall->rad->fan)

edit: the order you gave is a common setup for a top-mounted radiator.
 
Cyrusx7 said:
Either way, the fan should always send the air outside of the case, correct?
Click to expand...

Actually, you'll get better loop temps if the radiator has outside air bowing through it. Case air is warmer than ambient air, so sending air through the radiator right before exhausting it might hurt your temps slightly. It all depends on your overall design goals though. Many are of the opinion that, for top mounted radiators, it's best t work with the natural convection current, and exhaust case air up through the rad. For most other radiator placements lower in the case, the radiator will be set up so that colder ambient air is being sucked in throught the radiator.

Bear in mind that the parts that aren't usually watercooled are less temperature sensitive than the devices in your loop. So having your radiator exhausting case air will give you lower case temps, with higher loop temps. Having your rad on intake will give you lower loop temps, with slightly higher case temps. These differences tend to be fairly small though. You may or may not care about them.
 
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