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 Post subject: chimneys and cooling
PostPosted: Sat Nov 16, 2002 2:32 pm 
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Joined: Sat Nov 16, 2002 2:15 pm
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The first Macintosh used convection cooling, where hot air in the case would rise and exhaust through vents in the top of the case, and brought in cooler air through vents in the bottom of the case.

The computer would still get hot, so people started crafting "chimneys" out of foam core or cardboard that fitted over the top of the case, and some Macintosh shops even sold premade chimneys. A typical chimney looked kind of like an upside down funnel. People went through several iterations to find a good size and height for these chimneys. These chimneys significantly enhanced the convection cooling effect for the Macintosh.

These chimneys work like a fireplace chimney. The hot air rising through a fireplace chimneycreates something of a vacuum effect which pulls the smoke up through the chimney, which is why the smoke doesn't end up in the building. Some innovative architectural designs also use cooling chimneys to help keep the inside of a building cool.

Perhaps a computer chimney similar to the ones used for the early Macintoshes would be enough to cool a power supply or even a whole case.

JT


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PostPosted: Sat Nov 16, 2002 3:09 pm 
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Some experiments with "chimney" convection cooling of PSU here: http://www.silentpcreview.com/modules.p ... =15&page=1 -- especially on page 2.


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PostPosted: Sat Nov 16, 2002 4:24 pm 
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This article is what reminded me of the Macintosh chimneys.

I was thinking maybe a chimney added to the top of the vertically oriented power supply might enable fanless operation without giving up adequate cooling.

Another thing is a chimney added to the top of a computer case (some cases already mount a cooling fan that vents through the top of the case) would let you get rid of your fan cases.


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PostPosted: Sat Nov 16, 2002 5:38 pm 
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you're talking about the cube. it's infamous for being very unstable. all cube users hate it unless you only use it for 5min at a time to e-mail people and think they're 'cute'.

personally, i think you need an active cooling design to cool anything that'll dissipate more than 20w of heat. besides at 5v, most fans are really inaudible if you close the case and put the dynamat on the case.


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PostPosted: Sat Nov 16, 2002 6:55 pm 
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Location: Phoenix, AZ
Architects call this phenomenon the "stack effect"
I did some quick calculations with the following numbers:

Area of Opening: 6400mm^2 (80mm fan opening)
Height difference between intake and exhaust: 1 meter
External temp: 22C
Average Internal Temp: 38C

This gives a flow rate of 8.7CFM

This is almost the same as an 80mm Panaflo at 5v. The question is, is 1 5v Panny enough to cool your entire system?

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Senior Contributing Writer, SPCR


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PostPosted: Sat Nov 16, 2002 9:54 pm 
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Although the Macintosh "cube" also uses convection cooling, I was thinking about the original Macintosh 128K and Macintosh 512K ("Fat Mac").

If the entire case can't be cooled with a chimney, maybe at least the power supply could be adequately cooled this way. I'm currently cooling my 300W Antec and PowerMan power supplies with just an 80mm Panaflo at 5V.


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