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Case flow question.

P

Proxy

Pumpkin Ghost
Joined
Apr 24, 2005
Messages
4,308
Okay, on to a question I'm sure is asked a million times.

What is the best pressure (most effective for cooling) to have in the case? I don't care about dust as I clean my machine about once or twice every two weeks or so. Is it best to have a lower CFM fan for the intake and high for exhaust, vice versa, or about the same CFM on both?

Right now I have a low speed 140mm fan in the front, and a high speed 120mm in the back, however it does not seem like it gets the job done when things start to heat up, and yes my case wires are clean.

My case: http://www.performance-pcs.com/cata...=product_info&cPath=103_104&products_id=27762

Edit:

Picture:
021at.jpg


The only thing that has changed is the two GTX 280's have been replaced by a single 5870.
 
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id say run the same CFM for both if not more on the intake.. since you have extra vents on the case your better off trying to create positive pressure then negative pressure.. so higher CFM intake lower out take.. which will push more of the hot air out of the case instead of relying on the fan to try to remove it all..

also if those HDD cages are still in the case and are not being used id recommend removing them either stacking them on the bottom of the case or putting them away some where so that you have cleaner airflow coming from the front of the case to cool the 5870..
 
Cool thanks. As for the HDD cages, 3 of them are now populated, and I took the 4th out of the case. I think I am just going to get a new case soon. Lian-Li's are nice, but this design in particular is not friendly to air flow.
 
Airflow is airflow. Think of a single fan. However much air it's blowing out, it's also sucking in that much air too. It should move the same amount of air through a tube whether it's blowing into that tube or sucking out of it.

Now picture a tube with a fan on each end. If both fans are the same, it should flow that much air through the tube, obviously. If the intake is higher CFM, the exhaust fan will actually get in the way of the air trying to go out. If you've got 100CFM and 50CFM fans, you might only get 75CFM of airflow through the tube. Same thing if you have the higher fan on the exhaust. The intake fan will interfere with air trying to get into the tube, slowing airflow down as well.

Your case isn't a sealed tube though. If there's a difference between your intake and exhaust fans, air will flow through random gaps and holes in the case in an effort to equalize the pressure. With positive pressure, you'll be blowing extra air out those gaps, while negative pressure will be sucking air in. Personally, I think with positive pressure, you'll have a better idea of where the cool air is coming in (intake fans vs. gaps in the case), so you can do a better job of planning your airflow.

Also, I was told way back in the day that most HSFs blow air into the heatsink because it causes turbulence and makes the air tumble around against the fins. This allows more air molecules to come in contact with the heatsink and absorb heat. Likewise, blowing air into your case should cause the air to tumble around the components picking up heat. If you're trying to suck the air out of the heatsink or case, air (being a fluid) will tend to take the smoothest path out. An example (probably not entirely accurate) is a straw in your drink - does the liquid move around more when you blow into the straw or suck on it? The incoming air pushes the liquid all around, while it basically just flows smoothly into the straw when you're drinking.

Either way, I think you should try to get pretty close to an even in-out airflow, with fans strategically located to blow cool air to hot components and suck hot air out of the case.
 
That looks like a stock heatsink? There are so many after market heatsinks that don't cost much and will blow that thing away. Your airflow is important, but your heatsink is just as important. Check [H]ards budget coolers review, and this one also. That should help your heat problems.
 
Proxy said:
Cool thanks. As for the HDD cages, 3 of them are now populated, and I took the 4th out of the case. I think I am just going to get a new case soon. Lian-Li's are nice, but this design in particular is not friendly to air flow.
Click to expand...

Bingo.

The long video card acts as a dam for airflow from the front mounted fan and the drives help block its air also. So the front fan likely helps get some cool air into the video card very little maked it up to the cpu area and the warmth from the backside of the video card does.

If that was my case I would put a bay cooler in the top external 5 1/4 bays, dont need a jet engine fan just something that will shoot nice cool room air directly at your cpu area. Will work wonders. If you have too move the/a optical drives down so the bay cooler is lined up with the cpu fan as much as possible.

http://www.frozencpu.com/products/5..._Fan_Module_-_Black_CCFANMODULE_BZ-502B_.html

Lian Li makes one that will match, little pricey, I am not recommending that particular store one way or the other, just was first link I found on google.
 
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