Positive Air Pressure?

[freeagent]

A lot of fans sold today are whisper quiet, and you can blow harder then they can lol. I have 3 intake and one exhaust, they don't move very much air tbh.. barely enough. When you start getting into tri blade screamers and other industrial type fans then its another story heheh.

 

[magellan]

I don't like the mention of servers for the previous mentioned reason of the case not being remotely like ours. Pressure isn't mentioned because, like I have been saying the entire time its negligible.

Ahh forget it. Tberr was a reason a 487 post thread existed on this subject with no real answers... And as alluded to in my first post.. here we go again. I'm off this thread boys. Have fun spinning your wheels.

So because the case dimensions of a rack mount system are different there's nothing to learn from the thermal management techniques they use successfully?

 

[ShrimpBrime]

ShrimpBrine.... This is why these threads get derailed. .001 PSI and 5000PSI is still a pressure differential. The size of your fan does not change the science behind it.

Your right, You need to COMPRESS air to make a pressure.

You guys aren't compressing air, therefore you have NO case pressure.

No matter how much science you try to throw at it.

Work with PSI every day. Work with compressed air every day. It's under pressure when the pump is working.

If I remove the pump and and blow into the take while it has openings for air to escape renders no air pressure at all. just a flow.

Sorry but your fans do not compress air and you do not have "case pressure" period.

A fan moving air can only make a slight pressure directly in front of the blades. After distance the pressure the air can create onto an object, much like pressing your finger onto your arm, is a localized pressure, not a compressed pressure in a given container. Your case is a container and it is not pressurized.

NONE of you have any type of real "pressure" to speak or measure of. No matter how you try and word it.

 

[RGE]

So we have concluded there is no case pressure. And without pressure differentials, there is no air flow. I think I will look for physics refreshers elsewhere.

Nothing wrong with arguing no difference in cooling between negative and positive air pressure, or downplaying differential differences. But no need to go overboard and butcher physics.


Here is quote from one basic reference on Bernouilli principle, in this case an HVAC system, but any high school physics book will do:

Flow of air or any other fluid is caused by a pressure differential between two points. Flow will originate from an area of high energy, or pressure, and proceed to area(s) of lower energy or pressure. Conservation of mass simply states that an air mass is neither created nor destroyed. From this principle it follows that the amount of air mass coming into a junction in a ductwork system is equal to the amount of air mass leaving the junction, or the sum of air masses at each junction is equal to zero. In most cases the air in a duct is assumed to be incompressible, an assumption that overlooks the change of air density that occurs as a result of pressure loss and flow in the ductwork. In ductwork, the law of conservation of mass means a duct size can be recalculated for a new air velocity using the simple equation:
V2 = (V1 * A1)/A2
Where V is velocity and A is Area
The law of energy conservation states that energy cannot disappear; it is only converted from one form to another. This is the basis of one of the main expression of aerodynamics, the Bernoulli equation. Bernoulli's equation in its simple form shows that, for an elemental flow stream, the difference in total pressures between any two points in a duct is equal to the pressure loss between these points, or:
(Pressure loss)1-2 = (Total pressure)1 - (Total pressure)2
Conservation of momentum is based on Newton's law that a body will maintain its state of rest or uniform motion unless compelled by another force to change that state. This law is useful to explain flow behavior in a duct system's fitting.

And yes the case pressure is small in our computers, since scale of system case and fans are small and have little kinetic energy/static pressure, typical being 2-5mm h20. But really no different than using a box fan in a window of a 3500 sq foot house and doing a blower door test, scale is larger, fan is larger, but still setting up a relatively very small but effective enough to measure pressure differential.

And while I dont think it matters neg or pos pressure for cooling, this pressure can have effect on liquid cooling as has been indirectly measured by many with accurate equipment. Try blowing air through 2 360 rads, all expelling air into a case with only 1 fan expelling air. The air resistance from CASE PRESSURE, causes a 30% loss in cooling. Drop side panels, and delta air to water temps drop dramatically as the air moving through rad dramatically increases...not to mention the blowback of air over rad fans decreases.

So does discussing neg or pos air pressure help for air cooling, doubt it. Does it exist, it does if air flow exists.

 

[Luke1978]

Your right, You need to COMPRESS air to make a pressure.

You guys aren't compressing air, therefore you have NO case pressure.

No matter how much science you try to throw at it.

Work with PSI every day. Work with compressed air every day. It's under pressure when the pump is working.

If I remove the pump and and blow into the take while it has openings for air to escape renders no air pressure at all. just a flow.

Sorry but your fans do not compress air and you do not have "case pressure" period.

A fan moving air can only make a slight pressure directly in front of the blades. After distance the pressure the air can create onto an object, much like pressing your finger onto your arm, is a localized pressure, not a compressed pressure in a given container. Your case is a container and it is not pressurized.

NONE of you have any type of real "pressure" to speak or measure of. No matter how you try and word it.

you are 100% right, but when referring to positive or negative case pressure it isn't the... spirit of the word, for lack of a better term. It simply relates to the amount of air going out versus the amount of air coming in. This whole argument is foolish and been hashed over for decades.

I personally prefer as close to neutral as I can get. Some people will like what is referred to as positive, while others negative.

Sidenote, the newer series of "ACX" VGA coolers that come on cards Im not a fan of, because the are very poor at exhausting hot air outside the case, the older HIS IceQ cards and earlier versions of the ACX coolers actually had a sealed intake and so close to the PCB as to almost seal, so all the air coming in went out. Had to be taken into consideration when choosing how many fans and where to place them.

I've been out of the desktop world for quite a few years, but from my Athlon XP rig with an MSI 6200, to my San Diego 3700+ with an X850XT, to my opteron 148 on water with a 7800 GT to my last which was a phase cooled opteron 150 with 2 7800GTX's in SLI this argument hasn't changed 1 bit.

 

[magellan]

Temperature alone can affect the pressure seen in a container, assuming constant volume and moles of gas molecules in the container, a la' the ideal gas law:

PV = nRT

so compression is not the only way to increase pressure.

 

[magellan]

Your right, You need to COMPRESS air to make a pressure.

You guys aren't compressing air, therefore you have NO case pressure.

No matter how much science you try to throw at it.

Work with PSI every day. Work with compressed air every day. It's under pressure when the pump is working.

If I remove the pump and and blow into the take while it has openings for air to escape renders no air pressure at all. just a flow.

Sorry but your fans do not compress air and you do not have "case pressure" period.

A fan moving air can only make a slight pressure directly in front of the blades. After distance the pressure the air can create onto an object, much like pressing your finger onto your arm, is a localized pressure, not a compressed pressure in a given container. Your case is a container and it is not pressurized.

NONE of you have any type of real "pressure" to speak or measure of. No matter how you try and word it.

Interesting stuff. So all the CFM stuffed into a case by muffin fans just leaks out as fast as its shoved in? But if it's leaking out doesn't that mean the
case would have to be at higher pressure than what's outside the case, even if negligible?

 

[marjamar]

You guys like to talk I think... Reminds me of my step-father, uncle and one of my cousins about 20 years back. They all came to my home for a visit as 2 of them were on vacation from up north. It was a nice visit until my uncle started talking about a driveway he had put in. For the next 3 hours or more, all they did was talk about the same stuff about that driveway. I had to stay there, I was the host, but it started grating on my nerves so much I kept trying to alter the conversation. Inevitably the conversation kept going back to that driveway.

Another thing it reminds me of is that crazy Chevy Chase in European Vacation. That scene where he is driving his family to see the sights and gets caught in the go-around for all day into the night. It kinda felt like that 20 years ago, getting to feel like that again, so I'm sorry but I'm afraid I'm going to have to block you... Tell the mummy's they're blocked too.

-Rodger