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Fan physics

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December 15, 2010 12:22:24 PM

Hey there folks,

I have a physics/maths type question for you all.

I'm in the planning/design stage of experimenting with building a case from scratch, very low in height and very wide, kind of like a chunky benchtop. I'm planning to build it out of wood and glass (acrylic/polycarb is WAYYY too expensive for me, and I have some glass lying around the house). Internally, the space will probably be approximately 150cm W x 10cm H x 80cm D. Or thereabouts.

My understanding is that larger fans push more air for any given RPM and thus turn at a slower speed, therefore creating less noise.

As far as I can see, I have two options to choose from in terms of buying fans, which should I go for?

1. Multiple small intake fans on one side, air travels the 150cm across the components horizontally, and exits through multiple small exhaust fans on the other side.
OR
2. Fewer large intake fans on one end. Because they won't fit given that the height is only 10cm, I can try angling them, so that the air is sucked in in a diagonally upward direction, i.e. aimed at the top of the case. Hopefully the air will travel across the 150cm, towards the exhaust fans which are angled down and out at the other side.

Which option will be better in terms of firstly air flow and heat carriage through the case, and secondly noise production?

Does anybody have any other thoughts in terms of creating air flow for this short-and-wide case configuration?

Thanks, I'm interested to hear everyone's thoughts! :D 

More about : fan physics

a b K Overclocking
December 17, 2010 9:36:10 AM

I would stay away from having your fans at an angle. Even with them moving more air, because they aren't pushing air straight over the components I would have thought you could create a little air loop in the case and it wouldn't push air out the exhausts very well.

Smaller fans pushing air in a straight line and then exhaust fans pulling them out at the same angle would give best airflow I would have thought.
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December 17, 2010 1:39:36 PM

How about 3 large fans in the bottom and one exhaust at the top? Toms just did an article on a case setup like that and complimented them on using the physics of heat. IF your case design allows that ability.
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a c 126 K Overclocking
December 17, 2010 1:54:04 PM

Looks like you are building the top for a desk. Nice idea.

10cm high may work with low profile cards, but I think I
would add 2cm to allow for normal cards. That would also allow you to use 120mm fans.

1) My first pick for cooling would be to have standard 92mm intake fans in front, exhausting straight through to exit in the back. This gives you twice the amount of airflow vs. side mounted fans. Noise should not be an issue with good fans, but an alternative would be to locate the fans in the rear, with intake vents in the front. A short cooling path is the best.

2) For fans on the side, I would keep it simple with 92mm fans normally mounted. Unless you have hot components, cooling should be adequate.

3) If your intake area per fan is 100mm squared, you have 10,000 sq mm of intake area. Fans are round, so a 120mm fan will have about the same (11300) area to work with. I can see a reasonable case to tilt a 120mm fan to fit.
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December 19, 2010 2:02:34 AM

Thanks for the replies folks! A lot of good ideas to think about :D 
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December 19, 2010 2:02:51 AM

Best answer selected by outsidemyself.
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