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View Full Version : Positive pressure vs negative for cooling


grey_1
01-27-08, 09:21 AM
I found a couple of older threads, but we have new folks here also with their own ideas...

So I'm wondering what some of your experiences are. I'm designing a case from scratch basically, and I've read a ton of discussions over the pros and cons of both. If it makes a difference, there will be absolutely nothing in between the front and rear fans but mobo and the usual equipment.

It seems to me that negative would be best, as air pulled into the case wouldn't have the time to warm up, that there would be a smoother, more consistent flow of air. Given correct fan placement of course.

What are your opinions guys? Thanks.

EciDemon
01-27-08, 09:53 AM
But it would acumulate more dust no ?
It's ages since I red about these things, but I think it was positive pressure makes dust stay way.

I got tired of having so many fans in my system so I removed most of the extra ones. Kept one 80mm in the front where my HDDs are mounted so it blows some air onto them.

mullet
01-27-08, 10:22 AM
Positive pressure always.

1. this will keep dust from entering the case.
2. this will make it to where you can predict the air flow in your case from the front intake to the rear exhaust.
3. the whole secret is to change the air in the case as fast as you can, with less noise. I would use 120mm fans only if possible.

My case has 3 120mm for intake and 2 120mm exhaust with a 6-fan adjustment controller. This way I can keep a positive pressure inside the case.

grey_1
01-27-08, 10:44 AM
At the moment I have (All on paper only at this point) 3 120mm exhaust and 2 intake. The intakes will be filtered of course. Nice thing about this is it's easy for me to change at this point. :)

I'm also trying to build this so I can add water later, so I'll be able to drop the number of fans.

Drolfrawd
01-27-08, 04:06 PM
I found a couple of older threads, but we have new folks here also with their own ideas...

So I'm wondering what some of your experiences are. I'm designing a case from scratch basically, and I've read a ton of discussions over the pros and cons of both. If it makes a difference, there will be absolutely nothing in between the front and rear fans but mobo and the usual equipment.

It seems to me that negative would be best, as air pulled into the case wouldn't have the time to warm up, that there would be a smoother, more consistent flow of air. Given correct fan placement of course.

What are your opinions guys? Thanks.

Hello again , I have had this idea for some time , so here goes , Firstly my college tutor laughed at me fot this , but i'm willing to take a chance.

We have air cooled

We have water cooled

But what about liquid nitrogen!!!!!!!!
My thoughts are these , if a core of liquid nitrogen were rapped in a composite material , (engineers your thoughts), so as to allow a certain amount of coldness to be against components such as the cpu , graphics card etc, there
would be no need for fans nor anything else.

Love to know what you guys think of this!

On topic though, i wouid go for positive , thus minimising dust.

grey_1
01-27-08, 04:15 PM
LOl, Ln2 is waaaay more hardcore than anything I would personally play with. :p

I'm taking you guys advice though, and will be setting this up for positive airflow. Thanks. :)

XDanger
01-27-08, 04:16 PM
http://www.tomshardware.com/2003/12/30/5_ghz_project/

Drolfrawd
01-27-08, 04:21 PM
http://www.tomshardware.com/2003/12/30/5_ghz_project/

My minds eye did not foresee frost, rather a nice small square attached to the cpu no bigger than a heatsink, but thanks for the picture from Toms Hardware

grey_1
01-27-08, 04:29 PM
My minds eye did not foresee frost, rather a nice small square attached to the cpu no bigger than a heatsink, but thanks for the picture from Toms Hardware
Storing the Ln2 in the container you mention would be problematic, not to mention how dangerous that substance is. I worked with it of and on a few years back and would just as soon keep my distance.

Chilled water is another story though. Nothing drastic as I'm not a hardcore overclocker like some here. A TEC set up....maybe. I have 2-3 months to decide, so no hurry.

Drolfrawd
01-27-08, 04:32 PM
Storing the Ln2 in the container you mention would be problematic, not to mention how dangerous that substance is. I worked with it of and on a few years back and would just as soon keep my distance.

Chilled water is another story though. Nothing drastic as I'm not a hardcore overclocker like some here. A TEC set up....maybe. I have 2-3 months to decide, so no hurry.


Lol It was just a mad idea i had at college.

grey_1
01-27-08, 04:49 PM
Lol It was just a mad idea i had at college.
Just make sure you post pics if you ever actually find a way to pull it off. :)

Drolfrawd
01-27-08, 04:52 PM
[QUOTE=grey_1]Just make sure you post pics if you ever actually find a way to pull it off. :)[/QUOTE


Probs never happen , but i will post if i ever do

XDanger
01-27-08, 07:01 PM
once again I say dry ice in a paper cup ftw

BCKator
01-28-08, 12:49 AM
I don't understand why people say positive=good negative=bad=dust. If you're not filtering your inputs then you will get dust, whether pushed in or pulled in. Now, I filter all of my inputs so I only want air getting into my case via these inputs so I run a slight positive pressure (so that I don't pull unfiltered air in via the cracks). I also try to close up gaps w/ tape and foam to eliminate un-wanted flows. As was said before, you want to move as much air through the case as possible so exhaust fans help. I also use ducts and foam inserts to limit the amount of "dead" air pockets and force the flow of air over the components to be cooled and force known hot air (from CPU/GPU/FETs) directly out of the case as much as possible. Restricting airflow is OK so long as you are restricting it to move over the things to be cooled. I try to only use quieter 120mm fans and fit as many as possible. I run at 5v under idle conditions (so noise is not an issue) and raise to ~10.5v as required via thermal-based fan control.

Slammin
01-28-08, 02:50 AM
I think it mostly depends on the case. Some cases do better with positive (usually the ones with an exhaust blowhole at the top), and some cases (like Antec Sonata) do better with negative, probably due to the vented side panel.

If positive causes hot spots, try negative, but i always go for slightly positive when I can get away with it.

XDanger
01-28-08, 01:42 PM
Not pulling out enough can let the dust settle, Is that what this + / - stuff is all about?

Libertysyclone
01-28-08, 05:00 PM
I have a 250mm in the front pushing into the case and a single 120mm in the rear pulling. I have VERY LITTLE dust issues in a unfinished basement.

I think people get WAY TOO crazy with fans. I have a Q6600 @3.6Ghz (stock cooler) 3 HDDs one being a raptor 4x1gb sticks of Ram, Razer Sound Card, 8800Ultra, Tesla C870. in my case and the hottest the CPU gets is mid 60's same with the GPU.

Hottest HDD is the Raptor X @ 25*C
Ram is slightly warm to the touch.

I think Volume has a lot more to do with cooling than the amount of fans.

Cliff Notes: Get the biggest case you can.

mullet
01-29-08, 12:07 AM
I have a 250mm in the front pushing into the case and a single 120mm in the rear pulling. I have VERY LITTLE dust issues in a unfinished basement.

I think people get WAY TOO crazy with fans. I have a Q6600 @3.6Ghz (stock cooler) 3 HDDs one being a raptor 4x1gb sticks of Ram, Razer Sound Card, 8800Ultra, Tesla C870. in my case and the hottest the CPU gets is mid 60's same with the GPU.

Hottest HDD is the Raptor X @ 25*C
Ram is slightly warm to the touch.

I think Volume has a lot more to do with cooling than the amount of fans.

Cliff Notes: Get the biggest case you can.


+1

einstein_314
01-29-08, 12:45 AM
I don't know about the biggest case idea. I'm currently in 3rd year mechanical engineering and have taken a few thermodynamics courses. Here's my thoughts.

First off, air is a terrible heat conductor. It sucks. So for good heat transfer out of your case, you need a high flow rate of air through it. You want that air moving relatively fast.

As for positive pressure vs negative pressure, ideally you would have a neutral pressure, that would reduce the load on the fans and you would get the fastest air flow out of them. I honestly don't think it makes that much of a difference though, at least from a cooling point of view. I tend to do positive pressure though. I find it keeps the dust down inside the case.

Libertyscyclone: Your comment about biggest volume I don't think is very good. I don't think having more volume in your case will improve cooling. Sure if you had more fans as well it might, but just increasing the volume shouldn't increase heat transfer. If anything it will just increase the number of dead air zones and you'll have hot pockets.

I think the best way to improve cooling is clean up your cables and have a nice stream of air flow from the front of the case to the back.

Riptide
01-29-08, 08:42 AM
What do you guys think of the Lian Li PC80?
http://www.newegg.com/Product/Product.aspx?Item=N82E16811112159&Tpk=N82E16811112159

Very nice yes? Lots of volume. But $400?? :(

mullet
01-29-08, 10:44 AM
Rip my case is based of that design and its only 239.00, with tons of room. water cooling room/PSU top or bottom........
http://www.newegg.com/Product/Product.aspx?Item=N82E16811112141
http://www.nvnews.net/vbulletin/showpost.php?p=1502312&postcount=9

Libertysyclone
01-31-08, 03:25 PM
Einstein_314; I agree with you I do think that you need to size fans per case and that there are dead spots, but I think a bigger case has better options I direct air it my case a few different ways, and I have great cable management.

Here is an older pic of my case. It now has the water cooling setup and a 120mm in the rear but air flow is still the same.

Same setup that I was 3.6Ghz stable on the stock Intel cooler.

I lowered my 5.25 res to direct the air from the inlet fan towards the mobo.

I have never seen the Raptor get over 25*C

My Ultra is in the 50's under load when the Tesla C870 is not in the case.

My only other plan is to get another 120mm and make a tube/shroud for the RAM/Chipset.

Also all my unused back expansion slots dont have covers/ I think this tends to make a neutral pressure which also makes fans more quite.

CPU/GPU temps go up 5-8*C with the side panel off.

http://i26.photobucket.com/albums/c133/libertysyclone/IMG_4400.jpg

Riptide
01-31-08, 05:13 PM
mullet I like that case and noticed it earlier. Seems like the extra 120mm cooling fans behind the hard disc drive cage in the lower front part might cut into the extra space you gain from the depth of the case. Still more room than my Tsunami though.

mullet
02-01-08, 12:37 AM
Yeah, I don't like the stock HD cages case manufactures make at all. They put a cage in the bottom front and by the time you put HD's in there the 120mm fan or 2 120mm fans have been blocked to where there is about no air flow at all. I know my case is huge inside but I am really happy with the fan configuration and flow. I can't wait to see the temps of say a Q9450 or maybe a E8400 with a T-UE120 compared to my E6600 and the Thermalright Ultima-90.

BTW Libertysyclone nice setup dude.