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Case CFM

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April 25, 2006 6:46:02 PM

What is better to achieve the otipimal case airflow? Having a few more CFM exhausting out or having a few more CFM coming in thru intakes? With the fans I plan on getting, I figured it to be about 95ish CFM on intake and right about 100 on the exhuast. I am trying to get maximum airflow versus minimal noise. Any thoughts or ideas? Thanks.

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April 25, 2006 7:21:38 PM

It is better to have more cool air coming in that out. Also it is better to have an intake fan than an exhaust fan, you know what Im saying. True, for every action there is an opposite and equal reaction, and means that if your fans are taking in 100cfm then on the otherside its' exhausting 100cfm as well. But like I said it is better to force cool air in and direct them to the components that needs cooling than sucking them in using the exhaust fan.
April 25, 2006 8:18:04 PM

Thanks I appericate the answer. Will need to reevaluate my intake fans abit.
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April 26, 2006 12:19:37 AM

Quote:
It is better to have more cool air coming in that out. Also it is better to have an intake fan than an exhaust fan, you know what Im saying. True, for every action there is an opposite and equal reaction, and means that if your fans are taking in 100cfm then on the otherside its' exhausting 100cfm as well. But like I said it is better to force cool air in and direct them to the components that needs cooling than sucking them in using the exhaust fan.


Uggh, unless you're pressurizing your case, air in = air out. So your first statement is confusing. You recovered by saying the "every action" bit. Your statement about directing cool air onto the hot surfaces is a key point. Increasing the flow velocity on the hottest spots results in higher heat transfer. Adding conductive surface area (like a heat sink) at those hot spots helps too.

Ideally, you will have your case ventilation as a whole work with nature and not against it. Heat rises so there's no real advantage trying to work against that natural phenomenon. Thus, a blow hole fan - or at the very least, a top vent - makes good sense. Another way of thinking about this is that you don't want dead air spaces anywhere, but especially you don't want any up high because the hot pockets will transfer their heat to the components that are up there, like the power supply, optical drives, etc., and the upper part of the case. Not only will that add stress to those components, but they will conduct a portion of that heat downward through the case.

Exhausting hot air near the source makes good sense too, so the HSF on the X1900 graphics cards are a good design, as is the Zalman 9500 CPU fan coupled with a rear case fan aligned with the 9500's flow. Some cases blow inlet air right over the hard drive and that's a good way to keep the HD cool but it does add heat to the case. I added a pair of HDs a month or so ago and the case temp went up about 3 degrees C relative to the CPU temp - and the CPU went up about a degree relative to the ambient temp. The best possible ambient air-cooled case design does not exist in my opinion. What you would want is a case where cool air is blown directly onto each heat source and then it is immediately exhausted. And the components that generate the most heat such as the GPU, the CPU and the PS should have the most heat sink surface area and large corresponding air flows. It would be a weird looking case, huh?
April 26, 2006 2:21:46 AM

From my personal experiences, you would want more exhaust fans, otherwise air inside the case just basically sits there. What case are you using? And could you explain how your cooling system is setup? For example, mine is like this: I use an Antec P160 case, with a 120MM Intake fan in the lower front of my case. I also have a 120MM Exhaust fan on the upper rear of my case. I have 1 92MM Vantec Tornado on my heatsink, and a exhaust fan on the videocard (X850XT PE). My PSU (Tagan 480W TG-480-U22) has 2 fans on it, which are both exhaust.
Here is a bad diagram of what mine looks like:

----------------------------
<-<-| |<-<- |
<-<-|_____|<-<- |
| |
<-<-| |
<-<-| |
<-<-| <-<-|<-<-
| <-<-|<-<-
<-<-| <-<-|<-<-
|___________________|
May 3, 2006 1:39:41 AM

Sorry took so long to get back to you all. Finals week. I have a Raidmax case. Right now i have 4 80mm fans for intake. 3 in front and one on the side panel. For exhaust, it has 2 80 mm below psu. PSU has a 120 mm on bottom and back. I know I shouldn't rely totally on PSU fans but they do exhaust some air, right? I have a 120 mm on my Thermalright XP-120. All together they sound like a small vaccumm cleaner.

My plans are go with a 120 mm intake in the lower front and one 80mm on the side panel. Keep the two 80mm in the back and mod in a blowhole. I have picked out three 80mm that turn a bit slower so lower dBA. There will be a few more CFM coming in than going out.

My temps are 40C on the mb and 44C on the CPU under full load running Prime95 torture. Running a AMD64 3500+ at 2.54 right now. I won't to overclock it more but need some better RAM. Are these temps ok? And how does my fan setup sound? once again thanks for help and/or suggestions.
May 3, 2006 3:25:06 AM

temps are fine
!