What direction should the heatsink fan face?

My current setup looks like the following:

Rear fan <----- Heatsink Fan <----- Heatsink
Case: Arc Midi R2
Heatsink: Scythe Ashura with stock fan

I've placed the fan so it sucks the air out of the heatsink and blows it towards the rear fan. However, on several review sites, I've seen the fan face the opposite direction (and quite a lot of googled images):

The fan in the second image (same heatsink, same fan) blows towards the front of the case, so it goes:

Heatsink -----> Heatsink Fan -----> Front of case

Why is that so? From what I have read about the airflow, the goal is to redirect air towards the rear and the top. So why don't I simply direct it towards the rear fan instead of pushing it back to the front?

If I place my fan like this, will it improve airflow?

Boehmi

Posted 2014-07-11T14:45:12.383

Reputation: 171

1On the 2 pictures you linked to, those fans are blowing the air towards the rear of the case. They're just on the other side of the heatsink "pushing" the air instead of "pulling" it. – An Dorfer – 2014-07-11T14:48:06.840

But for the stock fan for the Ashura heatsink, the arrow points in the direction of the logo. Didn't the arrow indicate the direction the air gets pushed to? And the logo is in front in both my setup and the second picture. – Boehmi – 2014-07-11T14:51:52.023

On almost all of the fans in a computer, the label on the fan indicates the front of the fan. Air gets sucked in from the front of the fan and exhausted out the back. That is the same for your fan/heatsink too - Packaging Picture.

– An Dorfer – 2014-07-11T14:59:52.687

1Hm, should've looked better at the packaging. So basically, I should either reverse the fan I currently got on (since according to that picture, I'd be sucking in air that is near the rear fan, which is hot), or put it on the opposite side, right? – Boehmi – 2014-07-11T15:03:11.517

It doesn't matter what side of the heatsink the fan is on, as long as the fan is blowing the hot air out the back/top of the case. – An Dorfer – 2014-07-11T15:07:05.483

Answers

Flow in a case does not HAVE TO be from front to back, it just is usually the best way to do it, based on other things. Front fan already installed flowing in, PSU fans blowing out.
There are other good reasons to flow from front to back, like the hard drives and ram do not get heated by the cpu and gpu.

There are people who have chosen to have the hot air blow forward in a case, because they like the heat to land there (warmth), They had cooler air behind the case, or they just wanted to be different. Some flow designs have exhaust out the top, they may choose to send the cpu heat more foreward to be pulled out by top fans.

If your case flows the heat from front to back , then the heat leaving your CPU should probably also flow out the back.
Because you have some lightweight vaccume pressure from the back case fan pulling heat through the cpu heatsink, you might instead put the fan on the other side and have it blow direct on the heatsink and again out the back.

Rear fan <---Heatsink <----- Heatsink fan
This would get a little of the push pull action going that 2 fans on the heatsink would do which is usually setup like this
Rear fan still <-------Fan2 <----- Heatsink <----- Fan1

When testing (more than once) sucking vrses blowing, all the tests I have ever done show that it is better to blow, to force air into a heatsink , as opposed to sucking it out of it. It should have depended on the actual air movement which on a lot of fans is not center at all, the hub is in the way , and much of the movement of air is at the ends of the fins. I would test it again, but without testing, I would always pick blowing Into the heatsink.
The only time I got any improvement with the fan on the other side pulling air through, was when the same fan was ducted direct to the outside of the case, so the heat from the cpu was direct to the outside via that fan. By the heat going direct out, the rest of the case was cooler, even though the cpu itself was a bit hotter.

From what your saying your flow arrangement isnt to the front, so like you I do not see any reason to send it towards the front, to just fight the flow and eventually head to the back anyway, turbulance has value :-) but exhausting the worst heat most directally out of the case is going to make the whole case cooler.

Psycogeek

Posted 2014-07-11T14:45:12.383

Reputation: 8 067

here's one set of benchmarks, showing push (blow) does better than pull (suck): http://www.kitguru.net/components/cooling/dominic-moass/fan-config-does-it-matter-testing-push-vs-pull-vs-pushpull/2/

– Jeff Atwood – 2017-01-16T09:28:47.850

And someone else made it a science project, push wins again: http://www.tomshardware.com/forum/335129-28-push-pull-tested

– Jeff Atwood – 2017-01-16T09:29:35.677

That second article @Jeff linked is very confusing. It seems to be saying in several places that push is more effective than pull. But then there's this sentence: "As the data shows, when a fan pulls hot air from a heatsink, it will perform better than a heatsink pushing the air." I suppose that's just a typographical error, but I can't be sure, and the data/graphs aren't loading for me for some reason (now, 5 years later). – Cody Gray – 2017-02-28T08:14:34.877

Of course, from my rudimentary understanding of physics, blowing makes more sense. When you suck air, its pressure is lowered, resulting in fewer molecules of air to absorb and carry away the heat. On the other hand, blowing the air increases its pressure, thus increasing the number of air molecules and their ability to carry away heat energy. Thus, theoretically at least, blowing would be more efficient. – Cody Gray – 2017-02-28T08:23:52.407

There are two types of air flows to cool the heat sink:

Forced cooling - cool air is pushed on the heat sink for cooling purpose
Induced cooling- hot air is drawn from over the surface of the heat sink to allow fresh cool air to fill the space which enables-cooling..

When to use which method?

If the surface to be cooled is small and also has limited air input to its surface used induced cooling. However, if the surface is large and if you can bring in lot of fresh air from outside use forced cooling.

Prasanna

Posted 2014-07-11T14:45:12.383

Reputation: 3 554

There are many cooling variations but arguably the most common approach will be to have:

Rear Exhaust Fax <--- Heatsink <----- CPU Fan

This will probably be appropriate for you. Make sure the front of your CPU fan is facing into the back of the heatsink, so it is pushing cooler air between the blades of the HS and out to the rear. This is where the exhaust fan(s) will take over, dragging this warmer air out of the case.

If in doubt about the direction of air flow through your CPU fan, apart from the labels and markings it may have, you should be able to figure out from the direction of rotation which way the air is going.

CJM

Posted 2014-07-11T14:45:12.383

Reputation: 2 512

-1

You want the coldest air possible being pushed or pulled through the heat exchanger for optimal convection-cooling. That air is found outside the case, typically at the front. I would leave the fans the way you have them.

If you want lower temperatures, you could fabricate or purchase a shroud that would go from the front of the case to the CPU fan, or look into purchasing a liquid cooler.

ronald

Posted 2014-07-11T14:45:12.383

Reputation: 1