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 Post subject: Theories on air cooling
PostPosted: Fri Nov 09, 2012 8:16 am 
Smithfield
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So here's a fun topic that seems to get tossed around as much as anything else: what's the ideal way to setup case fans on a completely air cooled system for maximum cooling? I'm no fluid mechanics graduate, but from what I gathered from other sources (notably Silverstone) and some knowledge gained back as an engineer in school, I thought of the following:

  • You'll want more air per given space in the case than in the environment. So-called positive pressure. This has the effect of all the little cracks in your case pushing air out (mitigating dust build up) and prevents recycling of hot exhaust air (which some will get sucked into the holes that don't have a fan blowing out). So this implies that your intake CFM should be greater than your exhaust CFM.
  • While having a clean stream of air from one end of the case to the other is ideal, I don't think it really matters. Here's the thing: if a component needs airflow to cool down, it will have a fan with it. This fan will blow air across it better than any airflow the case fans could generate. Not to mention, I'm pretty sure a fan cannot accelerate air faster than a given velocity. A fan is designed to push air, on the same token, air can push a fan.
  • Top exhaust fans are counter-intuitive if your intake CFM < output CFM. Yes, convection does cause hot air to rise and perhaps collect, but most of the heat is in the middle, where your graphics cards are. The average temperature inside the case is going to rise before top exhaust fans will have any real effect.
  • On that note, the idea for the intakes it to bring in cold air as much as possible, thereby lowering the average temperature inside the case. This is so active cooling components have cooler air. Yes you could lower the average temperature in the case by blowing out hot air, but you run the risk your case having negative air pressure. Not only that, a top fan that's an intake would blow colder air directly on your VRMs and Processor... so doesn't that sound more beneficial?

In any case, this video alone pretty much convinced me of a lot of things.


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 Post subject: Re: Theories on air cooling
PostPosted: Fri Nov 09, 2012 10:12 am 
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I think it depends on the case itself, I use a nine hundred with one intake and two exhaust. one in the rear and the top oversized fan, the case has perfed covers on the front and the side as well, I pull air in everywhere and all of it is exhausted at the top and back, never had a cooling problem, although I use water cooling for the cpu and southbridge so airflow is just not as important for cooling as it would be if everything was air cooled. the only thing that really needs to have an airflow is the video card which runs at 35c with an 80% fan speed.

running this way, with mostly exhaust pressure gives me lots of fresh cooler air directly to the intake on the video card and across the hard disks, before the water cooling, I ran mostly zalman blooming flower or the big v shaped zalman heat sinks and I also have another machine in a thermaltake box with one of those hug fans on the side as an intake, although it is used with water cooling as well. (I bought two of the original corsair nautilus 500s) when they first came out and am still using them, about 5 years now.

I think about the opposite of you on air flow though, I use more exaust than intake to draw air in all the perforated sections that were put there for that purpose, allow air to enter and cool hard disks and fresh air to the video card and hsf the pic with the smoke seems to flow mostly to the rear and seems kind of dead in the rest of the case.


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 Post subject: Re: Theories on air cooling
PostPosted: Fri Nov 09, 2012 10:30 pm 
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Wonder what that smoke would look like in my case... only exhaust fans are at the top of the case, everything else is pulling in fresh air. Lower half of case is geared towards cooling GPU, with 4 fans directing airflow towards GPU two of those also cooling HDD/SSD. While upper half is geared towards cooling CPU with upper rear fan as intake blowing cool air across RAM & into H100 radiator mounted to top of case.


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 Post subject: Re: Theories on air cooling
PostPosted: Sat Nov 10, 2012 4:37 am 
Clawhammer
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Fans? Who uses fans? Passive cooling is king!


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 Post subject: Re: Theories on air cooling
PostPosted: Sat Nov 10, 2012 8:59 am 
Smithfield
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kleinkinstein wrote:
Fans? Who uses fans? Passive cooling is king!

Uh-huh. Let me know how getting a GTX 670 cool goes.


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