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Airflow Questions. PLEASE HELP

post #1 of 15
Thread Starter 
Alright. I am confused. Perhaps there is a sticky for airflow. I am sure if there is someone will link it.

Here is one thread I found on Tom'sHardware.

I have seen a lot of different cases and have owned a few myself. I have done a bit of research to boot. But, I don't pretend to have an in depth knowledge that some people may have. I will explain what knowledge I am after.

Positive vs. Negative air pressure
? Positive is more air coming in than going out. Negative is more air coming out than going in. I would think the main focus is to take the hot air out. A wind tunnel effect is best. However, would that not indicate that negative is better? What design would best promote this if that is true?

Is static air pressure important? From what I can tell it is if you want to push air through something. So would it matter as much for the exhaust as it would the intake? Or would it be just as important for the exhaust? Link 1 for static air pressure via Wikipedia. OCN thread talking about it.

Which matters more, static air pressure or CFM? In this application I think I have found CFM matters more unless you are wanting to push something like a CPU cooler or radiator. Here is a link to a thread I found on OCN.

Quote:
Originally Posted by DuckieHo View Post
Water analogy:
Static Pressure = Water Pressure (how hard the water is flowing)
CFM = Flowrate (how much water is flowing)

Electrical analogy:
Static Pressure = Voltage
CFM = Current

In low resistence area (i.e. case), static pressure doesn't matter that much. In high resistence areas (i.e. like the fins of a heatsink), higher static pressure is need to "push" through the fins.
Quote:
Originally Posted by RussianGrimmReaper View Post
In a high resistance environment, air moves much slower if it doesn't have high static pressure.

It's like comparing a pipe, and a pipe with a filter. The liquid in the pipe without the filter will move much faster than the other one.

Same thing with air.


Why don't more cases have vents/exhaust fans on the top of the case to expel heat and prevent trapped heat? Hot air rises so this would make sense for a good design. Some cases are considered top of the line like Lian Li, but don't have this as a standard minus the Lancool series.

I saw the Silverstone FT02B and while I think it has flaws and it's own issues, I love how it uses the fact that hot air rises. However, it would seem too easy for hot air to get trapped up top and circulate in on itself as there are three 180mm fans pulling air in and one fan pulling air out (top middle). Converse to this is the Corsair 600T which has a 200mm in the front, and 200mm up top, as well as a 120mm fan in the top rear. The problem with that case is it doesn't do a great job pulling air in due to static pressure. The NZXT goes one further and has a 7 fan capability and the idea is to be able to suck a lot of air out (depending how you set it up). Is a there a school of thought here that is a better one?
Edited by RoddimusPrime - 3/28/11 at 3:12pm
post #2 of 15
for cases you want air flow over static pressure, and you want it to be possitive so that all air going into your case is filtered and keeps down on dust.

For heatsinks and Rads you want static pressure, which is the amount of force a fan can push on a solid object.

the best way to for a case to be setup is for the the side and front to be intake and the top and rear to be exhaust, bottom would be intake if you have bottom fans.
post #3 of 15
Thread Starter 
Quote:
Originally Posted by thrasherht View Post
for cases you want air flow over static pressure, and you want it to be possitive so that all air going into your case is filtered and keeps down on dust.

For heatsinks and Rads you want static pressure, which is the amount of force a fan can push on a solid object.

the best way to for a case to be setup is for the the side and front to be intake and the top and rear to be exhaust, bottom would be intake if you have bottom fans.
If you have more air going in than out would the temp. not rise after a while if more air is coming in than out? Not saying you are wrong, but I see two camps. One positive stating what you said and the other being negative and creating pressure by pulling more out than in.
post #4 of 15
Quote:
Originally Posted by RoddimusPrime View Post
If you have more air going in than out would the temp. not rise after a while if more air is coming in than out? Not saying you are wrong, but I see two camps. One positive stating what you said and the other being negative and creating pressure by pulling more out than in.
pressure doesn't really effect the temp of the computer, as long as you have air flow. The only reason saying you want positive pressure is so that all air entering the case is entering through the intake fans which can be filtered. If you have negative pressure then air will be sucked in from everywhere which can't be filtered. But normally you want only a small amount higher intake then exhaust, just enough to make it positive pressure.
post #5 of 15
Thread Starter 
Quote:
Originally Posted by thrasherht View Post
pressure doesn't really effect the temp of the computer, as long as you have air flow. The only reason saying you want positive pressure is so that all air entering the case is entering through the intake fans which can be filtered. If you have negative pressure then air will be sucked in from everywhere which can't be filtered. But normally you want only a small amount higher intake then exhaust, just enough to make it positive pressure.
Filtered as in only coming from those intake fans or filtered as in dust filters or both? I live in a house with a lot of dust and pets.
post #6 of 15
Get a server grade case. I used to go with Chenbro. The pedestal case I always bought came with killer fans. 100cfm +
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post #7 of 15
Quote:
Originally Posted by RoddimusPrime View Post
Filtered as in only coming from those intake fans or filtered as in dust filters or both? I live in a house with a lot of dust and pets.
Filtered as in the fan has a mesh filter on it to prevent dust from getting in.
post #8 of 15
Thread Starter 
Quote:
Originally Posted by quadx View Post
Get a server grade case. I used to go with Chenbro. The pedestal case I always bought came with killer fans. 100cfm +
Ummm.... thanks. But that answers none of my questions.
post #9 of 15
Quote:
Originally Posted by RoddimusPrime View Post
If you have more air going in than out would the temp. not rise after a while if more air is coming in than out? Not saying you are wrong, but I see two camps. One positive stating what you said and the other being negative and creating pressure by pulling more out than in.
If there's constantly more air coming in than out, won't your case explode after a while? I should think that the pressure inside would increase to a certain level before the pressure decreases the cfm and increases the static pressure? And increases the flow outwards.

more intake = less outtake? = more pressure = lower airflow = more outtake? = high airflow?
(something went wrong there)

...might seem confusing, but it all reaches an equilibrium where everything stays the same, until you change the rpm of a fan or something.
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post #10 of 15
Thread Starter 
Quote:
Originally Posted by max it View Post
If there's constantly more air coming in than out, won't your case explode after a while? I should think that the pressure inside would increase to a certain level before the pressure decreases the cfm and increases the static pressure? And increases the flow outwards.

more intake = less outtake? = more pressure = lower airflow = more outtake? = high airflow?
(something went wrong there)

...might seem confusing, but it all reaches an equilibrium where everything stays the same, until you change the rpm of a fan or something.
I think a good comparison to make would be an extreme one. For instance a wind tunnel. Or a completely sealed unit using several configurations to see what is best. Certainly there has to be some kind of examples out there of people who have tested one theory vs. the other. Of course the end result is to keep your hardware cool in a quality case.

I am currently looking at some Lian Li cases like the A70f, but I need a top panel with grills spots for 120mm fans and I am also looking at the NZXT Phantom as well as the Silverstone FT02B. The latter uses intake on bottom and exhaust on top with a 90 degree angled MoBo.
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