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Difference Between Negative and possitive air pressure? - Page 4

post #31 of 43
Quote:
Originally Posted by PontiacGTX View Post

With 1 rear exhaust, 2 front intake 1 side intake reduced 13°C my GPU load OCed(460GTX)

Excellent start; now add fans one at a time to see if there's more temperature drop possible, or if adding fans creates higher temps (due to dead air/air conflicts etc.)
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post #32 of 43
Thread Starter 
Quote:
Originally Posted by MrHyde View Post

Excellent start; now add fans one at a time to see if there's more temperature drop possible, or if adding fans creates higher temps (due to dead air/air conflicts etc.)

let me have tempest 410(image with airflow I show at begging of thread)
post #33 of 43
On one case I have 2 front intake, 2 top intake, 2 side intake, and 1 rear exhaust. I have all the slot covers removed. The back of the case has air blowing nicely out of it. This has given me the best temperatures.

On another case I put one intake in front with higher CFM than a rear exhaust. CPU temperature dropped.
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post #34 of 43
^^^ THIS is why you test instead of guessing or speculating. thumb.gif
post #35 of 43
Quote:
Originally Posted by RedStapler View Post

I'm afraid I can't agree with this. Hot air still rises. Promise. Using a fan does not supersede the laws of thermodynamics. All other things the same, you will have better temps if you exhaust from the top. If you start moving hot air downward, it won't work as well, especially if you have positive case pressure. smile.gif

ONLY if you have positive case pressure will hot air ever be a problem in your case. Unless you have it setup with perfect intake/exhaust balance---and I don't just mean adding up CFM---you are going to have dead spots (traps) no matter what. You might not notice because overall your temps are probably better than they would be with no fans at all. But you can improve things pretty easily with negative pressure.

ONLY negative case pressure will ensure no traps--exhaust fans will create the most natural and efficient flow through your case as long as there is enough of an opening where you want air coming in.

On top of that, negative pressure (low pressure) facilitates high flow PER SE.. it's why push/pull coolers work a littler bit better---the pull fan is creating low pressure in front of the push fan, together making a more focused, higher rate of airflow in the area between them.

Try the same for the rest of your case: make the entire areas that are opposite your CPU and GPU be the exhaust (bottom and front). With enough CFM in one or two areas, you make effective low pressure right behind the exhaust fans, and any fans blowing air toward those areas is having an easier time.

Intake fans blowing too hard screw that up with traps and eddies (or straight-up conflicting airflow), or if they're blowing too gently, are obstructing the inflow made by your exhaust fans and forcing the cracks and seams of your case to take in more air to compensate (not necessarily bad, but you aren't getting max intake air focused where you want it.) So I just leave my intakes open, and air rushes in.

Here is my setup (mesh/grills cut out):

510

Why would I try and speculate on this? It *looks* wrong. But one day I broke two fans, another was always off balance so I decided to make do with one case fan, as a side panel exhaust. It's awesome and quiet.
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post #36 of 43

Hot air may rise when it's undisturbed, but it can't overcome even the lowliest fan.

 

Negative pressure may avoid any hotspots, but every crevice becomes an intake, and your case becomes a vacuum cleaner without the bag, filled with dirt. And if have a tight case and you put a really good fan on your exhaust, your case will hiss at you.

 

Positive pressure in cases was demonstrated years ago to create warmer temps than negative pressure.

 

What to do?

 

I have adopted what I call the positive flow method. I make sure that my case cannot build up any air traps. It has intakes from the side, top, front and bottom, and almost nothing in the back.

 

I cut out my rear grill. I left off my slot covers. Then I took my nibbler to the slot pillars -- those useless pieces of sheet metal between your slots. Air exits freely and softly. With no exhaust fan, nothing in the back contributes to noise. And all of my intake fans are behind filters. And because they run about 750-800 rpm, they make little noise.

 

Positive flow. Not any kind of pressure, positive or negative.

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post #37 of 43
Yeah, I go in with the vacuum hose for bout 3 seconds once every month or two, nbd. tiredsmiley.gif
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post #38 of 43
Negative pressure does not necessarily eliminate hot spots. Positive pressure does not necessarily increase temps. either.

Air flow is what is required to remove heat from the heat sources and exhaust it from the PC case.

The PC Cooling link below contributed by "MobAttack", illustrates some of the misconceptions about PC case cooling.

http://icrontic.com/article/pc_airflow_heat_cooling_guide

The only means to tell what works best for any given application is by actual testing.
post #39 of 43
Quote:
Originally Posted by samwiches View Post

Yeah, I go in with the vacuum hose for bout 3 seconds once every month or two, nbd. tiredsmiley.gif


Lucky you. I live with a bird that sheds off the tips of its feathers. I vacuum my filters every week or so. Easy to get to, so nbd. Still, there's no way I could make do with a negative pressure case.

 

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post #40 of 43
Quote:
Originally Posted by AMD4ME View Post

Negative pressure does not necessarily eliminate hot spots. Positive pressure does not necessarily increase temps. either.
Air flow is what is required to remove heat from the heat sources and exhaust it from the PC case.
The PC Cooling link below contributed by "MobAttack", illustrates some of the misconceptions about PC case cooling.
http://icrontic.com/article/pc_airflow_heat_cooling_guide
The only means to tell what works best for any given application is by actual testing.

Not surprised--the only two fully negative pressure configs were the best configs. thumb.gif

And that was before burning hot video cards. I don't want that heat going into my CPU, or anywhere but directly out the side panel.
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