Positive computer case pressure: myth? - Overclock.net

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post #1 of 84 Old 08-30-2016, 01:33 PM - Thread Starter
 
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Considering computer cases are hardly air tight it's hard to believe any measurable pressure could be created in them. Would it be possible to measure the pressure w/a barometer? Has anyone ever measured the pressure created in a positive pressure case?
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post #2 of 84 Old 08-30-2016, 02:54 PM
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You would need something more sensitive than a barometer.

With a computer case it really doesn't matter how much positive pressure, just so it's positive, so measuring would be kind of pointless.

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post #3 of 84 Old 08-30-2016, 03:49 PM
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The case doesn't have to be air tight. You just need more air intake than exhaust.
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post #4 of 84 Old 08-30-2016, 05:18 PM - Thread Starter
 
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Quote:
Originally Posted by billbartuska View Post

You would need something more sensitive than a barometer.

With a computer case it really doesn't matter how much positive pressure, just so it's positive, so measuring would be kind of pointless.

If it doesn't matter how much positive pressure there is then why does it matter at all?
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post #5 of 84 Old 08-30-2016, 07:06 PM
 
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Think he meant "as long as it's positive"

There is always pressure, both positive and negative have their drawbacks

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post #6 of 84 Old 08-30-2016, 07:36 PM
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Quote:
Originally Posted by 8051 View Post

Quote:
Originally Posted by billbartuska View Post

You would need something more sensitive than a barometer.

With a computer case it really doesn't matter how much positive pressure, just so it's positive, so measuring would be kind of pointless.

If it doesn't matter how much positive pressure there is then why does it matter at all?
You want positive pressure because the air from the intake fan(s) goes through a filter so there's no dust. The positive pressure also keeps dusty air from entering the case from any openings in the case.
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The case doesn't have to be air tight. You just need more air intake than exhaust.
Ah, the third law of thermodynamics says that can't happen. The amount of air entering and leaving the case is exactly the same. You need intake fans that have more pressure than the exhaust fans have vacuum, and the closer the amount of pressure is to the amount of vacuum, the less fan efficiency you loose.
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post #7 of 84 Old 08-30-2016, 07:42 PM
 
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Pressure doesn't build up in a PC case but compared to the ambient air pressure there is a force there. An example would be putting a box fan in your bedroom window and your door being forced closed on its own.

This has been demonstrated with smoke, showing that smoke is being forced out of all the gaps in a case with more intake than exhaust, and smoke (and dust) being drawn into the case when the other way around.
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post #8 of 84 Old 08-30-2016, 08:41 PM
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Quote:
Originally Posted by adamjp View Post

Pressure doesn't build up in a PC case but compared to the ambient air pressure there is a force there..
It may be just semantics, but no, the pressure does build up, but only to the point that it is enough to balance the CFM entering with the CFM leaving (in a "positive pressure" case). There is no other "force" involved other than air pressure. Barometric pressure isn't involved here as it it contributes the same amount of pressure inside and outside the case.
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post #9 of 84 Old 08-30-2016, 10:30 PM
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That skunk works video is at so full of garbage it's just stupid. It is rather obvious he either has no idea how airflow really works or is not able to explain how it works. 'Heat rises' is not at all true, While warming air causes it to expand and become less dense .. and this air is then push up by heavier air, case fans overpower this principle as soon as they start moving air.

The study of airflow is 'fluid dynamics'. Think of air as a fluid .. water. what goes into case must come out / what comes out must go in. Having slightly more intake potential then exhaust potential mean any vent without fans will leak air out not in.

Fans an create very little pressure. For example the difference in barometric pressure at sea level and 30 feet above sea level is 11.013 mm H20. The difference between sea level and 10 feet above sea level is 3.671 mm H2O. The fans we use in our systems have a static pressure rating of about half as much (1.836 mm H2O) or less.
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post #10 of 84 Old 08-30-2016, 11:20 PM
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Love these kinds of chats. Because every one holds good information, and nothing really misleading. It's a matter of perspective and an idea.

So we could rate your "positive pressure" in a case in different ways. Because there are so many different ways to USE these meanings, some of them do not apply.

______________________________________________

Looking at Fans and how they work.

A fan pushing air into a case works harder than a fan pushing air out of the case. When the exiting case fan spins faster because the "positive pressure" of the intake fan pushing air in, you no longer can consider yourself having any kind of pressure.

______________________________________________

Pressure. Must be measured in some way.

For example, to create a pressure of any true kind, you would pump more air in, and let less go out.

Example A.1 - The fan (or air pump if you will) can create a pressure perhaps in a sealed environment. So no exhaust fan.

Example A.2 - The Intake fan (with no exhaust fan) was able to create 1 bar or 14.5 PSI.

Example B.1 The "positive pressure" of 1 bar makes 14.5 pounds of pressure onto an object such as weight.

Example B.2 The "positive pressure" of my mounting bracket was increased by 14.5 PSI (because I modified it)

Example B.3 The barometric pressure is atmospheric pressure. If my windows are closed, it is likely not the same pressure inside as it is outside.

Example C.1 Cabin pressure. This is much like you in a plane that has an air pump that creates maybe 1 bar 14.5 psi.

Example C.2 Cabin pressure at sea level is about 1 bar.

______________________________________________

Really all you have is a case flow. Any kind of "positive pressure" would be negligible on your cooling. unless all you have is intake with out exhaust, no leaks.... you don't really have "pressure" that would be worthy of worrying about.

Should worry about obstruction free and even case flow more that anything. Move the air quickly to dissipate heat from the case faster. If you have 4 HDDs in front of your fan, that fan is not going to create any kind of pressure because there is too much obstruction.

A fan blowing on your heat sink most likely cannot create enough pressure to say it made my cooler seat tighter to the cpu because of direct flow. It's possible though. Just not with any ordinary case fan.

_____________________________________________________________________________________________________________

Static pressure of common case fans do little more than have a higher or cubic feet of air "moved" in a minute. Cannot create a "pressure" such as PSI above 1 bar, PC cases simply are not designed in this fashion. Neither are the fans.
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