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Old 10-31-2011, 07:36 AM   #1
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Default How the Case Rear Fan Improves CPU Cooling

There has been a new article posted.

Title: How the Case Rear Fan Improves CPU Cooling
URL: http://www.hardwaresecrets.com/artic...U-Cooling/1416

Here is a snippet:
"It is common sense that installing an exhaust fan at the rear panel of the case helps to cool all the components of the computer, including the CPU. However, most people don't know simple facts about ..."

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Old 10-31-2011, 09:01 AM   #2
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I liked this article. Simple, to the point, and consistent with common sense. I'd be interested to see if adding a low-front or BOTTOM fan further assists rising heat to escape.
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Old 10-31-2011, 01:00 PM   #3
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I've already suggested Rafael Coelho to make like a series, adding fans and seeing the impact on the CPU and VGA temperature.
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Old 10-31-2011, 05:37 PM   #4
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Default Suggestions

Hi.

Very nice article. I would suggest the following:

1- The vast majority of modern cases have the PSU at the bottom, circulating air outside of the casing. 2 things happen here. For one, there is no negative pressure created at the top of the casing forcing cool air upward. Second, PSU at the bottom obviously can't effectively act as a second exhaust fan.

2- Some high-end casing feature 2 back exhaust fans. Some other case give you the choice of 120MM or 140MM. Would be nice to test with 1 VS 2 fans and 120MM VS 140MM.

3- Same apply for large 200MM side panel fan or even top cover fan! Useless or actually doing some good?

4- I would like to know where we get to the point of diminishing returns. In order to move some serious air, I suggest you use the 12V 140MM Papst 5312 /2 TDHP. At 241 CFM, I'm sure you'll be able to hit the cooling wall!


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Old 10-31-2011, 09:28 PM   #5
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Nice article.
If i may add.

How's the performance on case that have rear fan and a top fan ?
Which is better. 1 x 200mm top fan or 2 x 120mm/140mm top fan ?
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Old 11-01-2011, 03:42 AM   #6
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We will try to make the same test with a bottom PSU case.
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Old 11-01-2011, 03:49 PM   #7
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Default A few hints

Silent and cool computing is a new game to you, I believe. Some basics:
Hot air rises.
Hot air rises.
Vent holes are not to be covered. See below, about pockets of hot air.
Dust isolate.
Motherboard as free as possible.
Harddisks low and cables high.
A big, strong exhaust fan creates the necessary air flow.
Intake fans are unnecessary, and can even create bad air-flow.
Bad air-flow creates pockets of hot air in various places in the case.

If you like to learn if your system got good airflow, take BIOS temp readings with case door open and case door closed; under heavy use and no use at all;-). Should temp drop dramatically with side door open, you have a case of a case with poor airflow. (I bet if so you have an intake fan. :-) )

To fix it, remove the intake fan, get a bigger/better exhaust fan, create a small hole in the side door, in level with or slightly below the graphics card.

About fans: Every case model is different, and PSU placement is not that big a deal; there are good things about it as well as bad. Fans come with printed information about how much air is pushed, sound level, max/min rotation. If it doesn't have that info. it is a fan you should avoid.

Last edited by Fredrik; 11-01-2011 at 03:55 PM. Reason: Adding
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Old 11-23-2011, 05:09 AM   #8
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I think the measurements with the case fan off are worse than they should be:
- The CPU cooler should be directed to blow the air upwards, towards the PSU fan.
- The case fan should be closed off to prevent air from being drawn in that way, completely bypassing the CPU cooler.

Quote:
Originally Posted by Fredrik View Post
Silent and cool computing is a new game to you, I believe. ...
... and to you too, it seems...
Quote:
Originally Posted by Fredrik View Post
Hot air rises...
... if left undisturbed.
In a computer the temperature gradients are small and there are fans all over the place.
Convection is pretty much a non-issue unless the computer is built without any fans.
Quote:
Originally Posted by Fredrik View Post
Vent holes are not to be covered.
Proper air flow management sometimes dictate that some vent holes must be covered to prevent loops where heated air is drawn back into the computer or cool air by-passing hot spots.
Open vent holes are also to be seen as "dust intakes". Dust is something you don't want a lot of inside the case.
Quote:
Originally Posted by Fredrik View Post
Motherboard as free as possible.
Good or bad depends on the overall air flow management.
Quote:
Originally Posted by Fredrik View Post
Harddisks low and cables high.
Again a matter of air flow management. Nothing always "right" or "wrong".
Quote:
Originally Posted by Fredrik View Post
A big, strong exhaust fan creates the necessary air flow.
A single strong fan can create a sufficient air flow, but isn't always the best option.
Quote:
Originally Posted by Fredrik View Post
Intake fans are unnecessary, and can even create bad air-flow.
Bad air-flow creates pockets of hot air in various places in the case.
Intake fans are great for catching dust in filters before it reaches the computer's interior.
Properly positioned and directed they help preventing hot air pockets.

One typical such pocket is underneath the graphics card, where unless fresh air is provided heated air will hang around and get re-used over and over again. Forcing air to enter or leave this pocket is crucial.
Quote:
Originally Posted by Fredrik View Post
... PSU placement is not that big a deal; there are good things about it as well as bad
I think it is a big deal because the optimum location depends on the computer design objectives.
A top placement is good for simplicity with as few parts as possible.
A bottom placement with separate air feed is better for low noise and mechanical stability (lower centre of gravity).
A bottom placement with the fan up helps cooling that potential hot volume below the graphics card (at the cost of more noise).
Quote:
Originally Posted by Fredrik View Post
Fans come with printed information about how much air is pushed, sound level, max/min rotation.
... and apart from the rotation speed this information is rarely reliable in the first place, and in practice it's nearly useless since the fan won't work with free air anyway.
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