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[ROG] Positive vs Negative Pressure - Page 3

post #21 of 44
Fail article is fail. The "pressure" is used in order to keep dust on the spots you precisely placed filters...not because of any other thing (and also because you tend to have more spots to place intake fans rather than exhaust ones).

Its also VERY funny that he uses an H50 as an exhaust...did he ever consider that he was doing it all wrong? rolleyes.gifrolleyes.gifrolleyes.gifrolleyes.gif
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post #22 of 44
proof.gif

I really don't think anybody is getting much of any pressure build up in their case with the cheesy plastic, low voltage , low cfm fans that everybody uses for computers, how much pressure do you think adds up with ten 120mm fans blowing in and only one out? Probably nothing close to any measurable amount or like the nerds like to say "differential" (makes me kinda sound like I know something),but that would imply it works.
Those fans can't produce enough air flow to create a positive build up inside the case ( or the hypothetical negative if your fans are backwards, lol), as with more pressure inside the fan needs to spin faster and be fed more power, to compensate for the difference, the fans basically just sit there and spin once enough "low pressure" builds up and they cannot effectively overcome any pressure wanting to escape, you know for every action has an equal and opposite reaction. At the point the fans can no longer increase their force from the presser wanting to escape they will be ineffective and probably start causing dead zones of airflow. If you have any fans blowing out the air will got to the place with the least resistance and increase the amount of air exiting on that fan than increasing any internal pressure.


Stick to overclocking everybody and leave the mind boggling concepts of pressure build up inside a computer case alone, these are the kind of fans that build up pressure http://www.chiblo.com/products/application.asp?app=5 These are the kind of fans for decoration and may throw a little bit of heat out of the case in the process http://www.newegg.com/Product/Product.aspx?Item=N82E16835553002

Want a little hands on ? , well just take something like a bread bag and put a case fan on the end of it, let it fill up and do a little testing, see how much weight you can add on top of that bag with all that pressure from that case fan blowing in. smil3dbd4e4c2e742.gif
Edited by JieMan - 3/19/12 at 8:46pm
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post #23 of 44
Quote:
Originally Posted by prava View Post

Fail article is fail. The "pressure" is used in order to keep dust on the spots you precisely placed filters...not because of any other thing (and also because you tend to have more spots to place intake fans rather than exhaust ones).
Its also VERY funny that he uses an H50 as an exhaust...did he ever consider that he was doing it all wrong? rolleyes.gifrolleyes.gifrolleyes.gifrolleyes.gif

What the hell are you saying?

My H50 is set up as an exhaust, what's wrong with that?
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post #24 of 44
Quote:
Originally Posted by Primus View Post

What the hell are you saying?
My H50 is set up as an exhaust, what's wrong with that?

Bill Cosby is not getting the static pressure to move stagnant air pockets within the H50 res, thus making a hotter CPU. That is unless you're blowing the exhaust from ambient case temps to cool a res? Just as bad.

Setup in a push/pull with fresh air moving into case, and through res.

I have an H50 and I have great temps for 5Ghz thumb.gif
 
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post #25 of 44
A pressurized case doesn't seem to be ideal from a scientific perspective. I assume "negative pressure" means vacuum and "positive pressure" means, well, pressure. When I clicked on this thread I thought it had something to do with positive and negative voltage pressure to create an electric current, but that's probably because I'm majoring in electrical engineering.

Anyways, pressurized air is generally associated with heat. When you pressurize something, the particles are closer together resulting in faster movement and more collisions, thus creating more heat in the process. Outerspace is so cold because there are not air particles (or any particles for that matter) colliding with each other to create heat. Also, we know, outerspace is a vacuum.


Sound doesn't travel in space either, which is another reason it is known as a vacuum. So I suppose i7Stealth1366 is right when he says there will be more noise smile.gif


Anyways, the only reason to have a fan blowing into the case is if it is directly over a component that produces a lot of heat. I try to counteract every fan blowing in with two fans blowing out. The main goal is to make sure the air is always moving quickly through the entire case.
post #26 of 44
I usually use the theories of convection when it comes to my builds. I have an h60 for my 2500k and a kuhler 620 for my gtx 580. I pull cool exterior air through the h60 which is mounted in the exhaust port of my case. The kuhler 620 is mounted on top of the HDD cage and pulls air through grills on the front of my case. I have one 200mm pulling air over the HDD cage on the bottom front of the case, a 120mm pulling cool exterior air over the vrm heat spreader of my 580, and all of this is topped off with a single 200mm exhaust fan that pulls hot air from the 580 and both rads out the top of the case. The way I see it is hot air wants to go one direction, up, so why not pull air from the bottom and just let convection do the rest of the work?
- chmodlabs
post #27 of 44
Quote:
Originally Posted by Kappy03 View Post

A pressurized case doesn't seem to be ideal from a scientific perspective. I assume "negative pressure" means vacuum and "positive pressure" means, well, pressure. When I clicked on this thread I thought it had something to do with positive and negative voltage pressure to create an electric current, but that's probably because I'm majoring in electrical engineering.
Anyways, pressurized air is generally associated with heat. When you pressurize something, the particles are closer together resulting in faster movement and more collisions, thus creating more heat in the process. Outerspace is so cold because there are not air particles (or any particles for that matter) colliding with each other to create heat. Also, we know, outerspace is a vacuum.
Sound doesn't travel in space either, which is another reason it is known as a vacuum. So I suppose i7Stealth1366 is right when he says there will be more noise smile.gif
Anyways, the only reason to have a fan blowing into the case is if it is directly over a component that produces a lot of heat. I try to counteract every fan blowing in with two fans blowing out. The main goal is to make sure the air is always moving quickly through the entire case.

While it is true that adiabatic contraction (expansion) causes air to heat (cool), low pressure doesn't mean low temperature. Temperature is a measure of the mean molecular kinetic energy and can be extremely high in low pressure situations, such as in the thermosphere (where temperatures reach 2000 C but the pressure is extremely low).
The pressure difference inside a case with 'positive pressure' isn't large enough to change the thermodynamics inside the case.
 
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post #28 of 44
I've tried testing this out in some of the other builds I've done and while the OP article is informative, I've only personally seen a change within say a margin of 10C overall. Unless for example you're not using case fans at all but I understand it was just done to show a starting baseline temp.

What I found with hot GPUs especially is that side ventilation is nice. More air moving through the case (intake or exhaust) beats just trying to build for pressure alone though the two tend to go hand in hand. A case with 3 fans (let's say 2 intake, one exhaust) simply won't tend to have temps as cool as one with more fans - or at least from what I've seen. Then again I might just be mistaken about the whole thing wink.gif
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post #29 of 44
Positive pressure just keeps dust out of your case o.o. pretty sure there are no thermal benefits. To most folks not worrying about dust is nice. I always use positive pressure for sff builds. Intake on the rads and no exhaust.
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post #30 of 44
Quote:
Originally Posted by chmodlabs View Post

I usually use the theories of convection when it comes to my builds. I have an h60 for my 2500k and a kuhler 620 for my gtx 580. I pull cool exterior air through the h60 which is mounted in the exhaust port of my case. The kuhler 620 is mounted on top of the HDD cage and pulls air through grills on the front of my case. I have one 200mm pulling air over the HDD cage on the bottom front of the case, a 120mm pulling cool exterior air over the vrm heat spreader of my 580, and all of this is topped off with a single 200mm exhaust fan that pulls hot air from the 580 and both rads out the top of the case. The way I see it is hot air wants to go one direction, up, so why not pull air from the bottom and just let convection do the rest of the work?
- chmodlabs

After reading this article when it was first published, I realized the force of convection is almost negligible unless your passively cooling all of your components.

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