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How To: Properly Plan And Pick Parts For An Air-Cooled PC, Part 2

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November 16, 2011 4:13:47 AM

Helpful even for myself (who has been building PCs for years). Granted all it really told me is that I was doing it right all along, but it did give me some useful bits of information that I didn't know before.

Kind of disappointed that the process of aftermarket GPU cooling wasn't explained more. That is something I have never done before, but always wanted to try out on one of my older cards.
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November 16, 2011 4:21:10 AM

gloves? who uses gloves :p  I use my finger :)  I have been doing it before there was even aftermarket paste :p 

the trick is, that i did and do twist, BUT i double check how much paste there is on the heatsink and the cpu, if there is enough I then fix it up on both ends and press the 2 together and do small twist... in fact if you have it lapped, you can twist a bit and it starts to give some resistance... IMO this tells me that access paste has distributed even and any access is gone...

This works so well that you cant separate the heatsink and cpu if you try to pull it straight off most of the time, but have to switch and move it.

How do I know it works? wouldnt be getting the results i did.. my old 720 be unlocked 4 cores and running at 3.3ghz .. I recently replaced it recently with Noctura D14 and phenom II X6, that I dialed into 4.13ghz

but then again I would say don't do this at home :p  (the way I do it works good enough when using thicker pastes, such as the arctic silver 5)

***I forgot to mention that this works for those heatsinks were you have a strap and not screws... I agree that those that have high pressure through screws you probably should not move or twist... but all those heatsinks that can create a lopsided effect due to the strap, this way works very well, especially when having thermal paste on both ends, and best way is to strap it down and take it apart, examine it and then fix it up add/remove any paste and place it back on.***

For the noob this is a good enough article...
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November 16, 2011 6:10:40 AM

On page 5 the second picture the top case fan points down yet hot air comes up.

Im curious although it wont have a large affect, if the CPU cooler fan would act like a puller if put on the left side whether it would hurt or help the memory temps
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November 16, 2011 11:05:53 AM

Really good article, and a real help. Just thought i'd chip in with what i know/have to ask....

I remember reading that sleeve bearing fans should not be used horizontally, that shortens the life span of the fan and makes it noisier over time. Something to do with the fluid in the bearing. Other bearings don't have this problem.

I also remember watching a program on NatGeo on submarines. Apparently modern day subs use propellors with a large number of thin blades. This basically avoids pressure diferences between water in front of the blade (in the direction it's spinning), thus prevents excessive low pressure in the region through which a propellor has passed. This avoids small bubbles of steam from building up and then popping, causing noise.

Seeing that air is a fluid too, i wonder if a similar principal will apply to it. Of course, there wont be any air bubbles popping in air, but i'm wondering if turbulence has any role to play, since i assume more blades=less turbulence. not sure though.

dB(A) is the A-curve...what about the C-curve? That's got more bass, which may be audible as a hum...C-cure measurements seem to ba a decible or three higher than A...

If the fans are connected to the mobo, you could use SpeedFan too...

With respect to the positive pressure section:
You say it goes against natural convection. What if i set the front and side panel as intake and the rear and top fans as the exhaust? I'm assuming the PSU is bottom mounted. Would it still go against convection?

What about neutral air pressure?

If, for example, the cooler needs to be re-seated following improper installation, is it a good idea to use isopropyl alcohol (Doctor's Alcohol) to clean the CPU and heatsink?

Cooler Master fans are pretty good, their higher quality fans 120mm fans move 79 to 90 CFM, their 200mm megaflow moves about 110 CFM. In both cases, rated noise is 19 dB(A). however, no rubber screws or frame so a that's a con.

BTW there's no prob with exposed heatpipes and the Arctic Silver, is there?
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November 16, 2011 11:55:49 AM

I've been doing the whole spread the paste evenly flat onto the CPU/Cooler for almost 8 years now. I'm not a professional when it comes to this solution, nor do i have eyes of a hawk to know if i do it right all the time, the temps seem to be right. I wish you guys did a temp difference on how the paste was spread in a lot different ways to give me a point of view of if there is any difference in temps, obviously the one where you can see the writing more then likely is not effective. Great article as always, cheers!
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November 16, 2011 12:06:21 PM

@ ojas

I'm not sure about all the other questions, but i know 90% isopropyl alcohol will work to remove thermal paste. "Goof Off" or similar products are even better. Also, i'd suggest using a coffee filter to apply the alcohol or goof off and wipe away the paste. that's what i do, works every time.
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November 16, 2011 12:28:13 PM

I read years ago that thinner the layer of thermal paste, the better.

Well...not THIN as in barely there thin but just enough to make lettering opaque, not completely covered.

I thought the paste is just to fill in cracks and imperfections on the heat sink and the surface of the processor...

also any word on Zalman's heat paste that comes in liquidy paste? it comes in a small bottle with a brush like nail polish...been using that all this time...
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November 16, 2011 1:13:40 PM

i've sometimes moved a fan's molex wires from 12v to 5v for silence's sake, but sometime it was too much. never knew i could get 7v by crossing the 12v and 5v lines like that (and wouldn't have dared try if i'd even thought of it anyway), glad to know there's another option there!
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November 16, 2011 1:13:46 PM

I would have liked to seen silverstone's air penetrater fans in here. Just to see how they stack up against other fans.
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November 16, 2011 1:40:28 PM

I think that you may have proven my case for GPU cooling being superior as a case exhaust design over the shroud design. The shroud design produces temperatures from 10-30 C above the case exhaust designs.

My own experience with a GTX 470 (from PNY) with a shroud showed an idle temperature abour 45-48 C. When I modded the card with a Zalman 2000F cooler the temperatures dropped to 30 C at idle. This (delta) temperature reduction was consistant for all uses: from idle to load. Similar loads produced temperatures that were 15-20 degrees C cooler with the case exhaust method over the shroud.

Just two weeks ago I added a second GTX 470 (from Galaxy) in SLI. This model has, what is touted to be, superior cooling to the reference design. It consistantly runs about 10 C hotter than the PNY cooled by thge Zalman aftermarket cooler at idle. Because of space considerations the shroud design had to be mounted above the case exhaust GPU. When the GPU load is increased the shroud design temperatures show a increase (delta) of 15- 20 C over the case exhaust. This is expected, as the top mounted GPU is the one with the major work load.

I ordered the mesh sided side door from Corsair (600T) to provide extra ventillation from a side panel fan blowing on the GPUs. If this configuration works, I expect a 5-7 degree C in the top mounted
GPU. I will be using the 200 mm fan (from Corsair) that was modded out from the top of the case when I replaced it with two 120 mm fans (from Xigmatek).
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November 16, 2011 3:06:26 PM

The Tcase Temperatures - Thermal Compund table states it's measured in Celsius but the comments below mention Kelvin.

Just to give you an idea of how different Celsius are from Kelvin, if the table states 58 degrees using the Nanoxia Nano TF1000 and they are Kelvin and not Celsius, that would be -272.15C (or -355F). That thermal paste would be hella better than liquid hidrogen!

I still agree that "differences of 1 kelvin can barely be measured consistently".

All in all, I like this articles. Keep the simple and efficient articles coming. Also the "advanced techie" ones... explained for us illiterate ones.
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November 16, 2011 3:17:32 PM

There are a few things I dispute.

For the negative pressure case:

Quote:
Amplification of natural convection


While the top fan blowing upward does indeed support (rather than oppose) natural convection, this is not a trait of a negative pressure setup. This is a trait of proper fan orientation (cover in the last article). Negative pressure means fewer particles available to transfer heat to. Thus negative pressure opposes natural convection. Conversely, positive pressure with a more particles available to transfer heat to supports natural convection. A good example of a properly oriented positive pressure system is the Silverstone Raven 2/ Fortress FT02.


Quote:
Compatible with all direct heat exhaust graphics cards (the ones that blow dissipated heat out of a vent built into the shroud)


Again, the more of a vacuum you create, the fewer the particles available, the worse the heat transfer. As a side note, fans are noisier in a vacuum as well, but I'll let you look into that if you're interested. In the setup your have, orienting the top fan downward would suck in some of the exhausted heat back into the case, but that again is a fan orientation issue. Again, the cases mentioned above post some of the best video card temps in the industry (especially for external exhaust style cards).


Quote:
Augments the cooling performance of downward-facing CPU heat sink fans


You'll have to explain this one to me, but I suspect this is another fan orientation issue rather than a positive vs negative airflow issue.


Quote:
Without a dust filter, dust gathers inside the case


Even with a dust filter, you have to understand that most cases aren't air tight. With negative pressure air will be drawn in through every crack, bringing dust with it.


For the positive pressure case:

Quote:
Only average cooling performance in enthusiast-oriented configurations


There are many counter examples to this statement. I'll stick with the Silverstone Raven 2/Fortress FT02. Though I do agree that if you orient the top fan down in the example case to achieve positive pressure, the improper orientation with drop your cooling effectiveness.


Quote:
Better support for graphics cards without the ability to exhaust dissipated heat


Not sure this is true either. While you do have more particles to work with, negative pressure systems tend to be better at directing airflow. This makes it easier to direct the heat away from the video card and out of the case. Of course, their are positive pressure systems that can achieve this as well.


Quote:
Counters convection


Only with an inappropriately oriented fan such as in the example you show. Not an inherent flaw of positive pressure systems.


Quote:
Air flow is determined by size/position of case openings


Having a hard time seeing this as a negative to positive pressure systems. This allows you to put the air where it is needed. I tend to think of a negative pressure systems more intuitive ability to direct airflow as a positive. If anything, it just requires more thought. At the opposite extreme, highly negative pressure systems can suffer from air coming in holes in the case and going straight out without doing any effective cooling.


Quote:
Counteracts the cooling performance of downward-facing processor coolers


Again, you'll have to explain this one, though I suspect it is an orientation rather than pressure issue.


Quote:
Graphics cards with DHE (direct heat exhaust) can partly counter the overpressure


This is true, but can't be considered a downside to cooling, especially when you already think the positive pressure systems don't cool as well. Rather it is something to consider (along with the PSU) as you design your cooling system.


A true downside to positive pressure systems is that you can get areas where air simply stagnates and doesn't get drawn into the flow. This leaves you only marginally better off than straight convection cooling. A good positive pressure case will make sure that air is still flowing around the components that generate heat.

In my findings, the best results come from a slightly positive pressure case. These still benefit from being able to direct the airflow for optimum cooling, while preventing dust build up and removing the vacuum effect. Though I must admit, the Silverstone Raven series/Fortress FT02 cases seem to get around these issues while remaining highly positive pressure. That said, fan orientation is of far greater concern, and should be setup to direct heat out of the case smoothly as shown in your first article. Improperly oriented fans will far outweigh the benefits of positive/negative pressure systems. In other words, make sure the case is designed for the type of system you want to implement rather than forcing the system you want on a case that isn't designed for it.
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November 16, 2011 3:22:33 PM

Where, in the U.S., can you get Xilence X5?
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November 16, 2011 4:26:32 PM

Another excellent article.

Also, good post from JPF on 1st page, altough I disagree that the (very) small variation in pressure would do any measurable harm to heat transfer. Smaller density has a bigger impact in the heat transfer through conduction, not much in convection.

From my experience, I could see that negative pressure inside the case did generate better temperaturas (most likely because you're able to direct the air by positioning fans acordingly).
Also, to help explain why negative pressure seems to bring in less dust, notice that the air is moving slower the farthest you go away from the fans, and slower air brings less dust in.
More fans bringing air in = more speed = more dust.
Less fans (and negative pressure) don't automatically mean less air will go in, but it does mean the air will enter slower (but through every possible little crack).

Ofc, please feel free to correct me if I'm wrong.

JPForumsThere are a few things I dispute.For the negative pressure case:While the top fan blowing upward does indeed support (rather than oppose) natural convection, this is not a trait of a negative pressure setup. This is a trait of proper fan orientation (cover in the last article). Negative pressure means fewer particles available to transfer heat to. Thus negative pressure opposes natural convection. Conversely, positive pressure with a more particles available to transfer heat to supports natural convection. A good example of a properly oriented positive pressure system is the Silverstone Raven 2/ Fortress FT02.Again, the more of a vacuum you create, the fewer the particles available, the worse the heat transfer. As a side note, fans are noisier in a vacuum as well, but I'll let you look into that if you're interested. In the setup your have, orienting the top fan downward would suck in some of the exhausted heat back into the case, but that again is a fan orientation issue. Again, the cases mentioned above post some of the best video card temps in the industry (especially for external exhaust style cards).You'll have to explain this one to me, but I suspect this is another fan orientation issue rather than a positive vs negative airflow issue.Even with a dust filter, you have to understand that most cases aren't air tight. With negative pressure air will be drawn in through every crack, bringing dust with it.For the positive pressure case:There are many counter examples to this statement. I'll stick with the Silverstone Raven 2/Fortress FT02. Though I do agree that if you orient the top fan down in the example case to achieve positive pressure, the improper orientation with drop your cooling effectiveness.Not sure this is true either. While you do have more particles to work with, negative pressure systems tend to be better at directing airflow. This makes it easier to direct the heat away from the video card and out of the case. Of course, their are positive pressure systems that can achieve this as well.Only with an inappropriately oriented fan such as in the example you show. Not an inherent flaw of positive pressure systems.Having a hard time seeing this as a negative to positive pressure systems. This allows you to put the air where it is needed. I tend to think of a negative pressure systems more intuitive ability to direct airflow as a positive. If anything, it just requires more thought. At the opposite extreme, highly negative pressure systems can suffer from air coming in holes in the case and going straight out without doing any effective cooling.Again, you'll have to explain this one, though I suspect it is an orientation rather than pressure issue.This is true, but can't be considered a downside to cooling, especially when you already think the positive pressure systems don't cool as well. Rather it is something to consider (along with the PSU) as you design your cooling system.A true downside to positive pressure systems is that you can get areas where air simply stagnates and doesn't get drawn into the flow. This leaves you only marginally better off than straight convection cooling. A good positive pressure case will make sure that air is still flowing around the components that generate heat.In my findings, the best results come from a slightly positive pressure case. These still benefit from being able to direct the airflow for optimum cooling, while preventing dust build up and removing the vacuum effect. Though I must admit, the Silverstone Raven series/Fortress FT02 cases seem to get around these issues while remaining highly positive pressure. That said, fan orientation is of far greater concern, and should be setup to direct heat out of the case smoothly as shown in your first article. Improperly oriented fans will far outweigh the benefits of positive/negative pressure systems. In other words, make sure the case is designed for the type of system you want to implement rather than forcing the system you want on a case that isn't designed for it.

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November 16, 2011 4:47:53 PM

Great article except for one thing:

"Be sure to set the T Junction correctly..."

Thanks, but how do we do that?

Anyway about case pressure, I tend to believe positive pressure is much better than negative. I was running negative for a while and it's so bad that the top fan on my Antec 900 couldn't push a small piece of paper in the air. I then turned off one of the exhaust fans and the paper flew off... so basically you definitely aren't going to help remove heat by having negative airflow if your fan can't even push enough air to move a small paper.

I'm currently running a front mounted 220 rad in push/pull, plus a 5th fan (Silverstone Air Penetrator) blowing at my 5850s (it's mounted using the "rear mount bracket" so it is spaced off the radiator by 2 fan widths). 5850s I switched coolers from stock (blower fans) to Scythe Setsugens (low profile with Scythe Slim fans) which reduced the noise. I also use a Scythe Slim on the side intake blowing at the gpus. With all that the cooler performance also increased over stock (with lower noise) - although without those 2 extra fans the cooling as a bit worse than stock.

Anyway I have temp probes setup (Scythe fan controller) for intake and exhaust temps. The intake is placed just in front of the radiator and the exhaust is just inside of the rear exhaust fan. Under normal usage the delta is about 3C, under gaming it's around 5C so not bad. I don't know if the probes are very well calibrated though, I haven't bothered to test that yet.

I'm also a little surprised about in Part 1 with the PSU bottom mount. Having an Antec 900 II the PSU has to act as an exhaust - you can't flip it without cutting the case. I assumed it was ok as it would help bring airflow along the bottom, although it does go opposite to the airflow of every other component. I guess I might have to try cutting a nice hole and flipping it over. That'll help cable management a little bit too haha.
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November 16, 2011 6:21:59 PM

An OK article. I was surprised the "line" method of applying paste is not explained, as this is what is recommended by many manufacturers (http://www.arcticsilver.com/pdf/appmeth/int/vl/intel_ap...).

I also think you are giving a little too much credit to convection. A 50rpm change in fan speed achieves more than convection every could. Convection helps passively cooled systems; in anything with a fan, convection is overshadowed.
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November 16, 2011 8:16:23 PM

Great article! And LOLed so hard at the end!!! :D 
I remember once when i had my old Athlon 64 3200+, i was checking why it was heating so much, I took the cpu cooler out and just then found I didnt have any thermal paste to put it back in... And it was some kind of holiday so it would take days for the shops to open again.. So i used oil (cooking oil) :p  I monitored temps constantly, fearing i had made a huge mistake, but to my surprise, it worked great..! It even kept temps even lower than before! :p  Played games and everything. A couple of days later i bought the paste and cleaned the mess, but temps didnt go any lower than with my "culinary fix"
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November 16, 2011 8:26:03 PM

I found out the hard way that the drop method (or any spreading technique as well) doesn't work for the newer heatsinks with exposed heatpipes. Here the best method is putting thin stripes of TIM on the heatpipes as they tend to be a little recessed to the plate.
It is the best way to achieve an even spread of the material with HDT type heatsinks, as recommended by Frostytech and many other hardware sites. Take my advice please, don't use the drop method with these type of HSF or you'll end up with an inefficient mess.
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November 16, 2011 8:42:12 PM

triculiousThe Tcase Temperatures - Thermal Compund table states it's measured in Celsius but the comments below mention Kelvin.Just to give you an idea of how different Celsius are from Kelvin, if the table states 58 degrees using the Nanoxia Nano TF1000 and they are Kelvin and not Celsius, that would be -272.15C (or -355F). That thermal paste would be hella better than liquid hidrogen!I still agree that "differences of 1 kelvin can barely be measured consistently". All in all, I like this articles. Keep the simple and efficient articles coming. Also the "advanced techie" ones... explained for us illiterate ones.


A difference of 1 Kelvin = A difference of 1 Celcius, the article said "differences of 1 kelvin" which is correct, there was only a difference of 1 Kelvin. Although I agree it is a bit weird changing between Celcius and Kelvin like that without any need.
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November 16, 2011 10:39:21 PM

The one thing that No one can seem to agree on is how to spread thermal paste. I remember when i was starting out i tried to find out the proper way some say grain of rice, some say enough to make it transparent, and yet others say none to just lap both the cpu and cooler and thats best. At the end i just gave up and used my finger to spread a little paste and just lapped my cooler not my cpu.
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November 16, 2011 10:45:25 PM

Great discussion of the various air flow models. Definitely time to replace my case.
For quiet operation what temperature should be set up for the case and CPU? Summer temperatures 35C+, thankfully low humidity!

I have dog, Dust can be a big issue. Not uncommon for cases to have quite large perforated grills and am not aware of any filters large enough. Any recommendations?

Are passively cooled PSU really an option?
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November 17, 2011 1:54:56 AM

Good article, but negative pressure ? Anyone commenting on this can simply disregard it.
You want to force cool air in and pull hot air out this is not negative pressure
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November 17, 2011 2:32:48 AM

should have tested Noctuna NT-H1 thermal paste. No curing time, i swear by it after using it just recently. Much better budget option than arctic silver.
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Anonymous
November 17, 2011 11:59:53 AM

Is cooling that important for many computers? I have always just run a CPU fan and possibly a GPU fan for years. Never a case fan found. My systems always ran until I sold them or retired them after 5 years.
I could still dig them out today. The question is more where your desktop is then how you cool it. Mine have always been in a basement office where ambient temp runs from low 70's to low 60's all year. That in itself helps with cooling. I am not saying people with higher demands such as the hard core gamer or the person who loves to over clock will not benefit from added cooling. I just question how much some with over spend and have to endure more noise for no real reason.
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November 17, 2011 2:10:26 PM


I finally found a very good way to cool a hot CPU in the "PSU Base-Mounted; CPU Cooler Vertical; Rear & Top Vents" configuration you describe. The only important difference is that my Coolermaster CM-690 case has two top fan ports instead of the one in your example. I put an exhaust fan in the rearmost of these top panel ports, augmenting the rear panel exhaust fan. I put an intake fan in the foremost top port; there it blows cool air down to the DRAM and the intake area of the CPU fan. Both top panel fans were 120mm Scythe Kama Flex with a PWM control range of roughly 300-1600 RPM. These have fluid bearings for long life in a horizontal position where sleeve-bearing fans would fail early.

The key to success was the Akasa AK-CB002 PWM splitter ($4 at PerformancePCs). This lets you control up to three PWM fans from the single CPU fan PWM (4-pin) header on the motherboard. It has a large Molex connector so that all the fan power comes directly from your PSU. I used this PWM splitter to power the CPU fan and the two top panel fans. The rest of the setup is as you show: a front panel and bottom panel intake, and rear panel exhaust. These three fans run full speed at 1100-1200 RPM.

In normal operation the system fan / air noise is audible, but unobtrusive. Under heavy load the CPU fan spins up and brings the top panel intake and exhaust fans with it, providing plenty of air even for an overclocked quad-core. And this arrangment maintains positive pressure because there is always significantly more intake than exhaust capability. This prevents dust buildup on the internals. Of course all the intake fans have filters, and I chose a good CPU cooler. If a hot graphics card needs even more air, add a side-panel intake fan at 1100-1200 RPM.

The above scheme is reliable, relatively cheap, and almost fool-proof, using only the PWM CPU fan control found on any quality mobo. It will give you a quiet but thermally very capable machine.
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November 17, 2011 3:20:49 PM

I will add that if your case does not have two top ports (vents), but does have a side panel port, you can use that as the PWM-driven intake. So this scheme can be applied to most of the more modern (bottom PSU) enthusiast-class cases. Also, I did try having both top panel PWM fans be exhausts but that was definitely inferior. It may seem strange to blow air down from the top, but in this configuration it works well.
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November 17, 2011 8:00:18 PM

ojas said:
I also remember watching a program on NatGeo on submarines. Apparently modern day subs use propellors with a large number of thin blades. This basically avoids pressure diferences between water in front of the blade (in the direction it's spinning), thus prevents excessive low pressure in the region through which a propellor has passed. This avoids small bubbles of steam from building up and then popping, causing noise.

Seeing that air is a fluid too, i wonder if a similar principal will apply to it. Of course, there wont be any air bubbles popping in air, but i'm wondering if turbulence has any role to play, since i assume more blades=less turbulence. not sure though.
The bubbles are called cavitation, and yes they make noise. You may have noticed that many companies make a marketing point out of nine-blade fans over seven blade varieties. This is a similar principle. More blade edges closer together ( up to a point, anyway, ) generally makes for smoother airflow and less noise.
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November 17, 2011 8:04:50 PM

icepick314 said:
I read years ago that thinner the layer of thermal paste, the better.

Well...not THIN as in barely there thin but just enough to make lettering opaque, not completely covered.

I thought the paste is just to fill in cracks and imperfections on the heat sink and the surface of the processor...
That is correct. Metals in the CPU heat spreader and the cooler base have better thermal conduction than the paste itself, but the paste has better conduction than air. If you have tiny air pockets between the CPU and the cooler, they act as insulators and heat builds up. If you have too much paste, then heat isn't transferred to the cooler as well as it could be, again resulting in minor insulating characteristics.

Ideally you want just enough paste to bridge any tiny gaps between the heat spreader and the cooler, then let the cooler do its job.
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November 17, 2011 9:10:00 PM

JPForums said:
There are a few things I dispute.

For the negative pressure case:

Quote:
Amplification of natural convection


While the top fan blowing upward does indeed support (rather than oppose) natural convection, this is not a trait of a negative pressure setup. This is a trait of proper fan orientation (cover in the last article). Negative pressure means fewer particles available to transfer heat to. Thus negative pressure opposes natural convection. Conversely, positive pressure with a more particles available to transfer heat to supports natural convection. A good example of a properly oriented positive pressure system is the Silverstone Raven 2/ Fortress FT02.
Someone already commented that convection and conduction are not the same thing. Convection is simply the movement of molecules within the fluid. Conduction is the actual heat transfer to those molecules. Less pressure actually means less resistance to the molecules to be able to move about, so yes, negative pressure can help convection.

As for opposing the conduction itself, that's debatable. Yes, you may have fewer particles to conduct the thermal energy, but then again Boyle's Law states that the remaining gas will suffer a temperature drop due to the drop in pressure. Newton's law of cooling states the rate of heat loss is proportional to the temperature differences between the two bodies, so cooler air will help cool the internals faster. The reverse is also true in that higher pressures will increase conductive particles but also increase ambient temperature.

However I don't feel the urge to do all the math to see if the an ever so slight difference in air temperature will offset the marginal conduction difference of gas density. Let's be realistic, we're not talking about huge differences in pressure or temperature here. I'd be shocked if you could sustain even a 1 psi difference in either a positive or negative pressure inside a computer case, let alone a 1°F difference. You get more difference than that in 2000 feet of altitude, so why aren't computers in Denver burning out every day?


JPForums said:
Quote:
Compatible with all direct heat exhaust graphics cards (the ones that blow dissipated heat out of a vent built into the shroud)


Again, the more of a vacuum you create, the fewer the particles available, the worse the heat transfer. As a side note, fans are noisier in a vacuum as well, but I'll let you look into that if you're interested.
And again, we're not talking huge vacuums here either. I'd also be interested in how you figure a fan is noisier in a vacuum considering there are fewer particles to carry the waves. Consider how sound is conducted not only faster but clearer when conducted through liquids and solids.


JPForums said:
Quote:
Augments the cooling performance of downward-facing CPU heat sink fans


You'll have to explain this one to me, but I suspect this is another fan orientation issue rather than a positive vs negative airflow issue.
It's easier to direct airflow with a negative setup than a positive one, particularly within irregular spaces. Downward CPU coolers basically recirculate whatever air is around them. A negative pressure setup will help evacuate that air, especially in the diagram they presented where the two exhaust fans are quite close to the CPU.


JPForums said:
Quote:
Without a dust filter, dust gathers inside the case


Even with a dust filter, you have to understand that most cases aren't air tight. With negative pressure air will be drawn in through every crack, bringing dust with it.
And even with positive pressure, some dust will build up inside. I think you're taking this point a little too literal.


As for the rest of your arguments, the images in the article are what they're using as an example for their statements because those types of cases with those fan configurations are about the most common available to the average consumer. Keep in mind, this article series isn't intended for the computer expert who uses the latest custom cases. This is meant for the beginner enthusiast who is more likely than not using fairly standard parts, meaning a case with fan mounts on the front, top, and back and maybe on the side. You can't "put the air right where you need it" if your case can't mount a fan there ( and I don't think the beginning enthusiast is willing to cut up and mod a case to do so. ) I love my Raven 3 case, sure, but most newcomers aren't willing to spend more than $60 on a case, let alone $150+.
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November 17, 2011 9:28:42 PM

ErelyesAn OK article. I was surprised the "line" method of applying paste is not explained, as this is what is recommended by many manufacturers (http://www.arcticsilver.com/pdf/appmeth/int/vl/intel_ap...). ...


In this case, not so, and your link proves the point, the line method is only for certain models of CPU,
and that link refers to Intel chips. Some Intel chips though are best done using the dot method
described here which is indeed also the method recommended by AS for Athlon64 X2 CPUs. In some
cases, AS suggests the surface spread method; it varies.

For this article though, the correct method was used.

Ian.

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November 17, 2011 9:37:16 PM

erelyes said:
I also think you are giving a little too much credit to convection. A 50rpm change in fan speed achieves more than convection every could. Convection helps passively cooled systems; in anything with a fan, convection is overshadowed.
Yes, a fan can overpower the direction of convection. But why have them fight when you can use them together?
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November 17, 2011 10:09:08 PM

spentshells said:
Good article, but negative pressure ? Anyone commenting on this can simply disregard it.
You want to force cool air in and pull hot air out this is not negative pressure
Care to back that up on why a negative pressure system won't work?

Seriously people, stop treating positive/negative like you've got a hermetically sealed case with 10 psi pressure change. With all the differences in case sizes, shapes, fan mounting, fan speeds and CFM, how can you say one or the other is superior in every situation?

Basically, it goes something like this: Positive pressure is great if you've got lots of fan mounting options to direct the air exactly where you need it ( as in right over cooling fins. ) Just make sure the back end of that directed airflow has a ready exit or you can develop eddies that keep hot air recirculating in the case. Negative flows can be better if you've got a stuffed case where all the components make a lot of hard angles for air to flow around. The downside here is that air will take the shortest, most direct route toward the vacuum, which may or may not have it pass over heat sinks.

But really, no one uses a pure positive or negative cooling system anyway. Everyone will have both intake and exhaust fans, so that even if you have a net positive or negative pressure, you can still route the air just as you need it without any problems.
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November 18, 2011 3:06:25 AM

RedJaronAnd again, we're not talking huge vacuums here either. I'd also be interested in how you figure a fan is noisier in a vacuum considering there are fewer particles to carry the waves. Consider how sound is conducted not only faster but clearer when conducted through liquids and solids.


While i see sense in most of your points, i think JP has a point here. I don't know if he's thinking what i'm thinking, but what i think he means is that:

A fan is noisier in a vacuum because of the whine it emits because of a pressure change. Go to your bathroom, leave the door open and turn the exhaust fan on. Note the noise. Now close the door. See what i mean? The fan seems to struggle to spin (unless your door has enough space to let air in)...and it creates more noise...i don't exactly know why, but i think it's a pressure thing. You suddenly lower the pressure inside the bathroom and the exhaust fan has to fight the atmospheric pressure, which it sort of fails at. Makes more noise too, but that's because of the stress on the motor i think.
Even though you have less particles, but the fan frame also makes more noise now because it's picking up increased vibrations from the fan motor. That adds to your contact surface with the particles.

In the computer's case, this vibration would be transmitted to case body too, which is generally steel, resulting in that loudspeaker effect or whatever you want to call it. Diaphragm effect seems more appropriate...

Cooler master specs their 90 CFM 120mm fans as creating 3.04 mm H2O of pressure. I really can't make much sense of that, i wish it was in atm, easier to get an idea. Will have to google or look in a book for mm H20 to mmHg conversion...regardless, doesn't seem too big a number.
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November 18, 2011 2:22:07 PM

Nice article. It made me realize that I used too much thermal paste when I recently built my new computer. However, the temps of my CPU are well withing the acceptable range even when playing BF3 on high settings.

However, I do intend to overclock my i5 2500k soon so I may remove the CPU cooler and reapply with a better thermal paste (and proper amount) than what I had used in the beginning.
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November 18, 2011 3:07:29 PM

I think I became more confused from this article and the reactions to it in the comments.

I have an Antec 300 and an Antec 600 (one of which I plan to use for my next build). I have a ZALMAN CNPS9900MAX-B heatsink. I see that most orientations have the heatsink blowing out the back of the case...is there a specific reason for this? Wouldn't it be more "natural" to position it to blow out the top of the case? Maybe out the back helps with directing the airflow better because you have the natural heat rising that still goes out the top? Maybe out the back draws more cool air from the front than it would from the bottom (directly above the GPU)?

I also have no idea about whether to try for a positive or negative airflow. I'm guessing that with the 2 120mm intake fans and the 120mm rear + 140mm top (1 200mm top in the case of the 600) it would be negative pressure? I was considering adding a 120mm side case intake fan to help with cooling the GPU and possibly modding in a bottom 120mm intake fan between the PSU and the hard drive cage. I'm guessing this would create a positive pressure airflow? Would this be overkill? From the article it seems like negative pressure is recommended...so I'm confused about what I should do.

One last thing...there are tabs about 1/2" above the floor of the case that the PSU will rest on. Will the approximately 1/2" gap between the floor and the PSU allow enough air so I can position the PSU face down or should I mod the case (I have no issues with cutting it up) with a cutout and filter under the PSU (or should I just face the PSU up drawing in (likely?) warmer air from under the GPU)? Will either of the face up or face down options with no bottom hole cut out contribute more to a negative pressure airflow?

Am I making too big a deal out of this and it probably doesn't matter much what I do?
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November 18, 2011 3:35:01 PM

A mm H2O is the same as a kg / m^2, or 9.81 Pascals, so 3.04 mm H2O is less than .005 psi ( basically, you can breathe with more force, admittedly the fan can sustain that pressure longer than you can. )

Decent point about the bathroom fan, ojas, and well illustrated. But I'm not sure it carries over. Between the drywall, topping compound, paint, and sealant, I'd wager a bathroom is better sealed than a computer case and the fan much more powerful too. Between all the seams in the case, venting mesh, etc, I don't think you could reasonably create a vacuum that would starve a case fan and make it work against itself ( unless you have every fan as an exhaust, in which case you've got bigger problems than just extra fan noise. ;)  )
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November 18, 2011 5:36:53 PM

RedJaronA mm H2O is the same as a kg / m^2, or 9.81 Pascals, so 3.04 mm H2O is less than .005 psi ( basically, you can breathe with more force, admittedly the fan can sustain that pressure longer than you can. )Decent point about the bathroom fan, ojas, and well illustrated. But I'm not sure it carries over. Between the drywall, topping compound, paint, and sealant, I'd wager a bathroom is better sealed than a computer case and the fan much more powerful too. Between all the seams in the case, venting mesh, etc, I don't think you could reasonably create a vacuum that would starve a case fan and make it work against itself ( unless you have every fan as an exhaust, in which case you've got bigger problems than just extra fan noise. )


Ah...thank's for the pressure conversion, been too lazy to look it up. That's tiny though :D 

I agree with you, a bathroom is much better sealed than a computer case, and the fan is far larger and more powerful. I just wanted to draw a comparison :) 

You're probably right though, a variation of 0.005 psi shouldn't really matter too much...and even if does make a difference, perhaps the same argument would apply to having positive pressure, because then you'd be making the intake fan fight against the higher pressure inside and become noisier...

which would make the entire subject of this "this pressure creates noise" discussion invalid, because now it seems to me that it should apply to both, so neither would be better. lol.

I'm still interested to know what happens in case of neutral pressure.
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November 18, 2011 5:57:08 PM

TopGun said:
One last thing...there are tabs about 1/2" above the floor of the case that the PSU will rest on. Will the approximately 1/2" gap between the floor and the PSU allow enough air so I can position the PSU face down or should I mod the case (I have no issues with cutting it up) with a cutout and filter under the PSU (or should I just face the PSU up drawing in (likely?) warmer air from under the GPU)? Will either of the face up or face down options with no bottom hole cut out contribute more to a negative pressure airflow?

If I understand this correctly, the PSU sits on tabs, raising it off the floor ot the case, but still enclosing the whole thing in the case? There might be enough clearance beneath it for proper fan breathing, but you're still running into the problem of feeding warmer air within the case into the PSU to cool it down. Now if your system doesn't run very hot anyway, that may not be a big deal.

But if you're willing to mod the case, I'd give the PSU a vent through the bottom of the case and then give it a proper stand so it sits at least an inch off the floor to let the PSU breathe from below.

But please, please people get your computers off the carpet. Seriously, am I reading some of these questions right? Did someone really ask if an intake fan could breathe through carpet? Even if it could, that's asking for a lot of dust, lint, hair, and carpet fibers to be sucked into your case, not to mention overtaxing your fan and risking static buildup.

Get your machines off the carpet, either on a desk or on a non-conducting stand.
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November 18, 2011 7:09:20 PM

RedJaron said:
If I understand this correctly, the PSU sits on tabs, raising it off the floor ot the case, but still enclosing the whole thing in the case?
That is correct.
RedJaron said:
There might be enough clearance beneath it for proper fan breathing, but you're still running into the problem of feeding warmer air within the case into the PSU to cool it down. Now if your system doesn't run very hot anyway, that may not be a big deal.
I doubt my case would run "very hot"...either way I doubt it will be a "big deal"...I'm just looking to optimize.
RedJaron said:
But if you're willing to mod the case, I'd give the PSU a vent through the bottom of the case and then give it a proper stand so it sits at least an inch off the floor to let the PSU breathe from below.

Get your machines off the carpet, either on a desk or on a non-conducting stand.
Ya, I've always put my PCs on some kind of hard surface (usually a wooden board or desktop). I'm definitely willing to mod the case, it's just a matter of is the extra time/effort/cost worth whatever benefits (if any) of adding a vent to the bottom of the case?

Any insight on my other questions?
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November 18, 2011 9:40:19 PM

For those who are confused: All discussions of "negative pressure" are moot, as I think spentshells was saying. Far offsetting any theoretical advantage it may possibly have is that fact that IT WILL CRAP UP ALL THE COMPONENTS IN YOUR CASE. Dust *will* be sucked in, and once you have a layer of that on everything, local heat transfer takes a nosedive.

You want positive pressure. You get this by having appreciably more intake capability than exhaust. That will give you PP even in a mesh case. Start out with at least one more intake fan than exhaust fans (including the graphics card exhaust if it dumps outside the case). *Then* decide where you want the flow, how much noise is OK, how much to spend etc. You can juggle fan speeds, sizes, and positions - but always maintain more overall intake capability than exhaust, at least under normal operating conditions.

BTW this is another advantage of the PWM arrangement I described earlier. It does not affect pressure balance even as it compensates for load.
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November 18, 2011 10:06:18 PM

TopGun said:
I doubt my case would run "very hot"...either way I doubt it will be a "big deal"...I'm just looking to optimize.
"Very hot" is a subjective term, and really I shouldn't have said that. It really depends on what kind of components your system uses, how they're configured ( mainly whether you overclock or not, ) and what kind of ventilation they get ( largely dependent on your case. )

A lot of Tom's heat reviews are done with overclocked hardware, which not everyone does. However, overclocked or not, most new video cards generate a lot of heat, and passing that hot air through the PSU is not the best idea. I can't say for certain whether it will prematurely wear down the PSU. Then again, if you're not planning on keeping the system, or particularly the PSU, for very long ( as in less than a year or two, ) then maybe you don't care if it wears a little fast. But if you don't have to do it, I wouldn't, just to be on the safe side.

To answer your other question, I believe the reason the most CPU coolers point toward the back and not the top is because until somewhat recently, cases didn't have vents on the top. Now they're fairly available, but the basic consumer case still vents out the back only. Also, Intel has square mounting brackets so if you want to point it up, you can. Sadly AMD mounts can't do this, though some coolers have brackets that can mount both directions on an AMD board.
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November 18, 2011 10:36:47 PM

Arbie, every computer, regardless of net positive or negative pressure, will accumulate dust on the inside. Yes, a net negative pressure in the case can attract extra dust around mesh vents and panel seams, but it won't appreciably deposit dust on the internals any more than a positive system would do.

All computers ought to be regularly cleaned out inside with canned air or some gentle vacuuming ( meaning a dustbuster, not a shop vac. ) Personally I do this about every six months.

But rather than worrying about negative and positive pressure, a better way to prevent dust in your computer is basic housekeeping. Get your computer off the floor and away from the carpet, change your furnace air filters regularly, vacuum your carpets, etc. This will make a much bigger difference in dust accumulation than any fan configuration.

And no, you DON'T need to start with an additional intake fan for positive pressure. With the huge variaty of fan size, speed, and efficiency, you can easily get net positive pressure with fewer intake than exhaust fans.
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November 19, 2011 6:44:27 AM

i've been an enthusiast for case intakes and exhaust combinations but found that the most annoying is the dust. aside from dust causing bad cooling performance, it also increases the frequency of cleaning the system which is to me is downtime for anything you do.

i discovered that the negative and positive case pressure is not really of a concern for cooling but dust control. let me explain.

intakes is only useful to cool parts directly with ambient air such as Harddisks, video cards, or cpu. you still need more exhausts more than your intakes to prevent heat buildup.
the problem with intakes is they suck in dusts. using a filter doesn't control dusts, it just blocks bigger dusts and lets in finer dusts. you could make a thicker filter but it wouldn't suck air enough.

for dust control, never use intakes only exhausts. seal all holes of a case on all its sides except for the hard drive side intake, a fine filter would do great. clear tape or sealants will do.
also, the type of case should have holes at its bottom for it is where the air will come in.

this setup works since dust would be sucked only from the bottom but wouldn't reach the computer parts due to lack of air pressure. with this, dust only settles at the bottom of the case, and table/floor.
i still haven't cleaned my almost 3 year old video card also with the help of its auto fan speed control. motherboard is almost clean as new. the cpu heatsink and fan was cleaned for the first time a month ago.
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November 19, 2011 10:52:02 PM

the excessive sized sythe 10mm fans was an interesting discovery for the accelero passive heat sinks, i will have to try switching an aero slot cooler for this option.
mjmjpfaffI would have liked to seen silverstone's air penetrater fans in here. Just to see how they stack up against other fans.

SILVERSTONE AP141 139mm Case Fan
Bearing Type: Fluid Dynamic
RPM: 1500 rpm@12V / 1000 rpm@7V / 700 rpm@5V
Air Flow: 28.26 CFM (5V) / 41.09 CFM (7V) / 64.34 CFM (12V)
Noise Level: 18 dBA (5V) / 20.9 dBA (7V) / 30.1 dBA (12V)
Model #: AP141
Item #: N82E16835220046
http://www.newegg.com/Product/Product.aspx?Item=N82E168...

IMO not a very good choice the 120mm 120mm
Bearing Type
Fluid Dynamic
RPM
1500 RPM
Air Flow
35.36 CFM
Noise Level
22.4 dBA

also not a very good choice, seems silverstone is still learning how to make fans.
my shopping search for fans is CFM then Noise then Price. only time i deviate is when i have a special need for a certain type of fan, like when i used sythes 10mm thick fans for tight spaces or axial fans for tight confined area higher needs cooling.
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November 20, 2011 6:35:21 PM

f-14 said:
the excessive sized sythe 10mm fans was an interesting discovery for the accelero passive heat sinks, i will have to try switching an aero slot cooler for this option.

SILVERSTONE AP141 139mm Case Fan
Bearing Type: Fluid Dynamic
RPM: 1500 rpm@12V / 1000 rpm@7V / 700 rpm@5V
Air Flow: 28.26 CFM (5V) / 41.09 CFM (7V) / 64.34 CFM (12V)
Noise Level: 18 dBA (5V) / 20.9 dBA (7V) / 30.1 dBA (12V)
Model #: AP141
Item #: N82E16835220046
http://www.newegg.com/Product/Product.aspx?Item=N82E168...

IMO not a very good choice the 120mm 120mm
Bearing Type
Fluid Dynamic
RPM
1500 RPM
Air Flow
35.36 CFM
Noise Level
22.4 dBA

also not a very good choice, seems silverstone is still learning how to make fans.
my shopping search for fans is CFM then Noise then Price. only time i deviate is when i have a special need for a certain type of fan, like when i used sythes 10mm thick fans for tight spaces or axial fans for tight confined area higher needs cooling.

thy direct air very well- http://www.youtube.com/watch?v=8m8fC809TK0
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November 21, 2011 7:44:36 PM

Zodiac, I can't disagree with that enough.


zodiacfml said:
intakes is only useful to cool parts directly with ambient air such as Harddisks, video cards, or cpu.
Um, that's incorrect on multiple points. First, all air cooling is due to lower air temperatures, so I have no idea where you're trying to go with this. Second, you mention air intakes are only good at cooling HDDs, CPUs, and GPUs. Well, considering those items contribute to the vast majority of heat in a computer ( the only other thing that comes to mind it the mboard VRM, ) why is that a bad thing?

But more to the point, air intakes are not only "useful to cool parts directly with ambient air." Intakes also serve an important purpose of directing airflow around in the case.


zodiacfml said:
you still need more exhausts more than your intakes to prevent heat buildup.
Care to explain this? Heat doesn't magically stay inside the case. Fluids flow from high pressure to low pressure, regardless of positive/negative sources. If there's a vacuum, air will rush in to fill it. If there's overpressure, air will rush away to equalize. Whether you're trying to expel hot air or pull in cool air, either way will work.


zodiacfml said:
the problem with intakes is they suck in dusts. using a filter doesn't control dusts, it just blocks bigger dusts and lets in finer dusts. you could make a thicker filter but it wouldn't suck air enough.
Intake fans don't mystically suck in dust. Dust is in the air, period. Whether it's pulled in by a fan or pulled in by the vacuum in your case, dust will enter.


zodiacfml said:
for dust control, never use intakes only exhausts. seal all holes of a case on all its sides except for the hard drive side intake, a fine filter would do great. clear tape or sealants will do.
Right, so the next time you need to replace or upgrade a part, you have to clear off all the tape and sealant? Worst idea I've heard all month. And didn't you just say that fine filters wouldn't let the case breathe properly?


zodiacfml said:
also, the type of case should have holes at its bottom for it is where the air will come in.
Wait, didn't you just recommend sealing all holes, vents, and seams except on the front of the case?


zodiacfml said:
this setup works since dust would be sucked only from the bottom but wouldn't reach the computer parts due to lack of air pressure. with this, dust only settles at the bottom of the case, and table/floor.
If you've sealed up the entire case, are using all fans as exhaust, and you're still lacking air pressure, that means you have poor air flow through the case, meaning poor cooling.


Cases are designed with vents in certain locations for very good reasons and suddenly sealing them up is not a good idea for a healthy and cool computer system. I'll say it again. If you're concerned about dust in your computer system, proper housecleaning has a much larger impact than fan configuration.
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Anonymous
November 23, 2011 2:59:45 AM

your positive pressure analysis...
I found to be completely wrong and infact completely opposite from my real world results and experience
another uninformative inspired toms article
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November 25, 2011 11:55:44 PM

My layout works well.

http://xyzcoord.webs.com/images/airflow.jpg

http://xyzcoord.webs.com/media/airflow.cortby.pdf

I have the case on its side with a 24 inch monitor on the top front of the case.
There is a 120 mm horizontal intake left front(bottom).
It blows through to the left (under) of drives to the GPU.
Behind the monitor is a 140 mm vertical intake on the top left rear blowing down onto the GeForce.
GPU: GeForce 470 has a 80 mm exhaust fan with a vented card slot.
Before I improved my case, the GeForce would crash when overheated.
There is a 80 mm vertical intake fan top center.
Under the fan is a telescoping tube to a 92 mm CPU cooler with 4 copper heat pipes.
CPU: Core 2 Duo E8400 3.0 to 3.6 GHz
There is a 120 mm exhaust in the rear and a vented card slot below it.
The 800 W PSU has a 120 mm bottom exhaust fan (now sideways).
I used clear package tape to seal all of the holes and slots in the metal case.
All of the intake fans have washable foam filter grilles.

The case is pressurized and I addressed cable management by folding them up to make an air dam between the pressurized GPU cell at the left bottom of the case. The cables are wedged between the end of the graphics card and the back of the drives and top of the case. The CPU is getting twin supercharged charged fresh air from the tube. The PSU is exhausting the blow-by pressure from the CPU, GPU cell and the front intake.

I fiddled around a few times before I arrives on this setup a few months ago. The twin chamber air dam of wires trick dropped both my CPU and GPU temperatures by 10 degrees Celsius average across the board. At idle or while gaming. I get 47 CPU - 50 GPU in Windows (at 3 GHz core#0, 607 MHz CUDA). While gaming I get 60 CPU, 70 GPU max (at 625 MHz CUDA). It is quieter and cooler after using my engineering skills to tinker one step at a time. -10 deg ain't bad.
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November 27, 2011 5:16:43 AM

I turned my top fan over to blow up and out, in the direction of convection.
I put washers between the fan and the removable side case to cure a rubbing noise.
The gap between the washers and the fan was sealed with black electric tape.
I scrubbed out all of the heat sinks, the CPU and inside of the GPU, etc. using an old soft tooth brush. Then I just had to air blast the leavin's.

Admitted: There was a just enough of crud on the front of the GeForce heat sink to affect my previous temperature readings. I clean the air filters on my case weekly and dust the inside monthly. The card was not even very dusty when I opened the case, but when I un-clipped the lid on the card I saw a little cotton candy dust bunny on the leading edge of a beautiful 5 heat pipe heat sink. There was not a lot at first but looking closer the little there was was in just the wrong place.

Gaming-HIGH
Before: CPU = 65 C. Before: GPU = 70C. Fan DOWN in
After : CPU = 55 C. After : GPU = 60C. CLEAN GPU + Fan UP out

Normal-IDLE
Before: CPU = 50 C. Before: GPU = 60C. Fan DOWN in
After : CPU = 45 C. After : GPU = 50C. CLEAN GPU + Fan UP out
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