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A rad Push-Pull radiator fan idea


Xyzzy Frobozz

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Hi all!

 

I've searched the whole interwebs to get a bit of an answer on an idea I've been kicking around in my head for some time. So far I'm yet to come up with an answer, so, being the Corsair fanboi that I am, I thought I'd come here for some good advice because, you know, Corsair people are knowledgeable people!

 

The idea is a very simple one. Most of us know that a push/pull fan setup on a radiator yields the best results, even if only a relatively small improvement on a simple push configuration. Again, most of us would know to use high pressure fans in such a setup.

 

But is it that simple?

 

My idea is fairly simple - use high pressure fans such as the SP120 on the push side, and then high airflow fans such as the AF120 on the pull side. The rationale for this is that the high pressure fans would have the "oomph" to push the air through the radiator gills, and the high airflow fans would then remove the air as quickly as possible once it had passed through the radiator. This may also create an area of low pressure after the radiator and therefore make the push fan's job a little easier and reduce time that warm air stays in the radiator by removing it more quickly. Another advantage may be that this would increase airflow within the case for those of us who place their radiator at the case intake.

 

It's a fairly simple and obvious idea, but one I am completely unable to find an answer on. I realise that the benefits may be small, but has anyone tried this or tested it? Does anyone have any thoughts on whether this would be a good/bad idea?

 

With the impending release of the Corsair 780T and G10 GPU brackets I'm beginning to plan a build that may include the push/pull idea.

 

Thoughts?

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Hi all!

 

I've searched the whole interwebs to get a bit of an answer on an idea I've been kicking around in my head for some time. So far I'm yet to come up with an answer, so, being the Corsair fanboi that I am, I thought I'd come here for some good advice because, you know, Corsair people are knowledgeable people!

 

The idea is a very simple one. Most of us know that a push/pull fan setup on a radiator yields the best results, even if only a relatively small improvement on a simple push configuration. Again, most of us would know to use high pressure fans in such a setup.

 

But is it that simple?

 

My idea is fairly simple - use high pressure fans such as the SP120 on the push side, and then high airflow fans such as the AF120 on the pull side. The rationale for this is that the high pressure fans would have the "oomph" to push the air through the radiator gills, and the high airflow fans would then remove the air as quickly as possible once it had passed through the radiator. This may also create an area of low pressure after the radiator and therefore make the push fan's job a little easier and reduce time that warm air stays in the radiator by removing it more quickly. Another advantage may be that this would increase airflow within the case for those of us who place their radiator at the case intake.

 

It's a fairly simple and obvious idea, but one I am completely unable to find an answer on. I realise that the benefits may be small, but has anyone tried this or tested it? Does anyone have any thoughts on whether this would be a good/bad idea?

 

With the impending release of the Corsair 780T and G10 GPU brackets I'm beginning to plan a build that may include the push/pull idea.

 

Thoughts?

 

Wouldnt work, you need high pressure fans to create a low pressure zone on the other side of the radiator to aid in airflow. and AF fan is useless in applications that have ANY restriction, imo theyre only good for case exhaust

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I'm almost certain, that for push-pull to work correctly, you have to have 4 identical fans, otherwise the airflow is disrupted.

 

agreed,one fan will impede the other but a push pull only gives a small marginal improvement of a couple degrees.

most do a push/pull for the look factor...

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Wouldnt work, you need high pressure fans to create a low pressure zone on the other side of the radiator to aid in airflow. and AF fan is useless in applications that have ANY restriction, imo theyre only good for case exhaust

 

See this is where I'm not so sure. I'm not saying that you're wrong mind you, it's just that I'm not sure it is so simple.

 

A high pressure fan makes an area of high pressure after the blades. So, whilst I agree that a high pressure fan would be best in the push position, if my theory is correct, the best way to make an area of low pressure after the radiator is to remove the air as quickly as possible with high flow fans. The rationale is exactly the same as why high flow fans are used as case exhaust - the air has already been pressurised, done its work removing heat, and now we want to remove it as quickly as possible in order to make more "room" for more air to get in.

 

As I said, I'm not saying that you're wrong, you could very well be correct, it's just that I'm not sure I see the point of high pressure once the air has passed through the radiator. To my mind, once the air has passed through the radiator and done its work carrying away heat, the imperative becomes moving it away as quickly as possible.

 

Perhaps this is why push/pull configurations only realise such marginal benefits - we've been doing it wrong?

 

Anyway, I was kind of hoping that someone had done some sort of testing or could give a "scientific" explanation, but perhaps it falls upon me to test it. Although I reckon the best people to test it would be Corsair, given that they have all that whizz-bang testing equipment from when they developed their fan products.

 

Hint, hint!

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See this is where I'm not so sure. I'm not saying that you're wrong mind you, it's just that I'm not sure it is so simple.

 

A high pressure fan makes an area of high pressure after the blades. So, whilst I agree that a high pressure fan would be best in the push position, if my theory is correct, the best way to make an area of low pressure after the radiator is to remove the air as quickly as possible with high flow fans.

 

As I said, I'm not saying that you're wrong, you could very well be correct, it's just that I'm not sure I see the point of high pressure once the air has passed through the radiator. To my mind, once the air has passed through the radiator and done its work carrying away heat, the imperative becomes moving it away as quickly as possible.

 

Perhaps this is why push/pull configurations only realise such marginal benefits - we've been doing it wrong?

 

Anyway, I was kind of hoping that someone had done some sort of testing or could give a "scientific" explanation, but perhaps it falls upon me to test it. Although I reckon the best people to test it would be Corsair, given that they have all that whizz-bang testing equipment from when they developed their fan products.

 

Hint, hint!

 

whizz-bang testing equipment,,lol,,,i like that

maybe im wrong also but here goes

theres 2 main differences among fans

one that pushes air but any obstacle greatly hinders airflow[freeflow fan]

the other is a ''static pressure'' fan where when a obstacle gets in the way [such as a radiator],it has the power to push air

about like a car that can spin its tires[sp] fan and a car that lacks the power to spin its wheels [free flow] ...

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whizz-bang testing equipment,,lol,,,i like that

maybe im wrong also but here goes

theres 2 main differences among fans

one that pushes air but any obstacle greatly hinders airflow[freeflow fan]

the other is a ''static pressure'' fan where when a obstacle gets in the way [such as a radiator],it has the power to push air

about like a car that can spin its tires[sp] fan and a car that lacks the power to spin its wheels [free flow] ...

 

 

Correct, that's my understanding as well.

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A high pressure fan makes an area of high pressure after the blades. So, whilst I agree that a high pressure fan would be best in the push position, if my theory is correct, the best way to make an area of low pressure after the radiator is to remove the air as quickly as possible with high flow fans. The rationale is exactly the same as why high flow fans are used as case exhaust - the air has already been pressurised, done its work removing heat, and now we want to remove it as quickly as possible in order to make more "room" for more air to get in.

 

As I said, I'm not saying that you're wrong, you could very well be correct, it's just that I'm not sure I see the point of high pressure once the air has passed through the radiator. To my mind, once the air has passed through the radiator and done its work carrying away heat, the imperative becomes moving it away as quickly as possible.

 

Well, you're ignoring a few significant facts.

  • Obstructions on the intake side of case fans significantly decrease their throughput. The airflow is disrupted, which separates the boundary layer from the blades; creating turbulence on the intake side, which cuts their efficiency. Take a case fan, point it at your cheek, place a pencil across the input side, run it laterally back and forth across the face and tell me what you feel.
  • Two fans in series need to be compatible in airflow. If either the first or the second is less capable, the other suffers. IOW, it isn't as if an individual fan is running in its own controlled environment; in a black box as if nothing else is around. The throughput is not absolute and independent of other factors; it is influenced by them.
  • Most who have tried and tested push/pull have found that having pull added does very little in the first place; other than giving the owner a sense of one-upmanship. In all actuality, the push fans alone could just run at minimum speed and do nearly as well as running full bore; due to the thermal capacity of the radiator alone.

 

Anyway, I was kind of hoping that someone had done some sort of testing or could give a "scientific" explanation, but perhaps it falls upon me to test it.

 

Have at it and let us know.

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Strangely enough, I have just installed an air cooler made by another company and in the instructions it says that if you buy and fit a second, 140x150mm fan, the new fan will spin at 1200 rpm whereas the one supplied with the cooler spins at 1500rpm. They recommend that you install the 1500 fan on the front of the cooler, pushing air through and the 1200 on the back pulling air through. This, they say will give the best performance. They also supply a cable to slow the 1500 down to 1200 if you prefer.
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There you go. Whatever the dynamic, the two in series need to be complementary. If the second fan were to rotate faster, it would be starved and suffer cavitation; thereby reducing its efficiency below a fan that is rotating at a proper rate.
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There you go. Whatever the dynamic, the two in series need to be complementary. If the second fan were to rotate faster, it would be starved and suffer cavitation; thereby reducing its efficiency below a fan that is rotating at a proper rate.

 

Air doesn't cavitate...

 

I remain unconvinced that the fans need to be the same design. This is the crux of what my post original post - that fans either side of the radiator have fundamentally different tasks.

 

On the push side, the fan needs to create enough pressure to force air through the radiator.

 

On the pull side there is absolutely no need to maintain pressure as there is no longer any resistance to airflow. As a matter of fact, we are actually seeking to create an area of low pressure before the pull fan blades by removing air as quickly as possible, thereby creating that pulling effect.

 

A gas will always move from an area of high pressure to one of low pressure. In the absence of any impediment to airflow post radiator, it's my current opinion that the best way to create low pressure post radiator is to move as much air as possible with a high flow fan.

 

I could be wrong, but I'm yet to hear a compelling reason why!

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A shortcut term. So sue me. The point is, that the efficiency of the fans will be diminished if the two fans are not matched. They do not have to match each other, they have to have their throughputs matched for this Rad idea to have any benefit at all. Otherwise the boundary layer of the blades will be separated from the surface and you end up with essentially the Equivalent Of Cavitation in a gas. I.E. turbulence and/or starving that could otherwise be avoided. Try progressively placing a card over the input side of a muffin fan and tell us all what happens.
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Well, I fitted the 2 fans the way the manufacturer said ( I'm being careful not to mention the manufacturer, as I got taken to task when I did that before) and it's both quieter and cooler than my previous H100i. Shame about the 2 tone brown colours of the fans.
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A shortcut term. So sue me.

There's no need to be like that, how was I supposed to know?

 

The point is, that the efficiency of the fans will be diminished if the two fans are not matched. They do not have to match each other, they have to have their throughputs matched for this Rad idea to have any benefit at all.

Right!

 

So by that logic having two fans of exactly the same design would cause problems, as the condition of the incoming air will be very different for the second fan as from the first. The first fan received unpressurised and unimpeded airflow.

 

The second did not.

 

Otherwise the boundary layer of the blades will be separated from the surface and you end up with essentially the Equivalent Of Cavitation in a gas. I.E. turbulence and/or starving that could otherwise be avoided. Try progressively placing a card over the input side of a muffin fan and tell us all what happens.

 

Not wishing to belabour the point, but to use that analogy, only one of the fans has the "muffin tin" impeding it in the form of a radiator.

 

I'm not trying to be difficult for the sake of it, but it is for this very reason that I am questioning it. When I put together my computer, my thought instantly was that the conditions for the second fan would be very different than for the first, so why put two of the same design on both sides. And why bother with a high pressure fan after the radiator when there is no longer a need for high pressure.

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