my "heat rises theory"

four4875 · May 13, 2003

i have a theory on why thinkin that heat rises in a comp is pointless. i think that it takes a while for heat to rise, and since we're rushing the air around in a case so fast, it really doesnt matter. anyone have any other thoughts on this? it juust seems like it this is true, we can toss out most of our cooling theorys.

sandman001 · May 13, 2003

well, yes and no.

If you do it this way you aren't working against the heat rising, but if you do push air in from the top then you are wotrking against any force it may have. While it may not make much difference, it can't hurt.

Nolo31 · May 13, 2003

Well, from what I understand, this is the science behind it:

Hot air does not naturally rise. Cold air is denser than warm air, so naturlly, since it has more mass, it goes as low as it can. This causes the hot air to rise.

With fan flow, it gets a little more complicated.

Diggrr · May 13, 2003

If you take into account that a humble stock case fan moves a 30-60 cubic feet of air per minute, and your case is only 4 cubic feet, then there's no time for hot air to rise.
I think it all got started with how normal cases are built to hold the components...your cpu, power supply, and cd drives are all mounted toward the top of a case, and are all major heat sources.
Now maybe your case metal would get warmer near the top of the case because 2 out of 3 of these components are directly mounted to the case, but I wouldn't think the air would have much chance to flow convectively.

If you take the no-case approach like I do, then surely even without case fans, there's no chance of hot air being in the top of a case that isn't there.

four4875 · May 13, 2003

i think diggrr knows exactly what i mean.... lol

Carnil · May 14, 2003

The airflow from the fans will overwhelm the "heat rises" effect for components in the airflow (usually the CPU, power supply, and northbridge), but for components outside the flow, such as the video card, modem, and sound card, convection is how the heat generated enters the flow to be exhausted from the case.

wheatbix · May 14, 2003

I agree with what everyone else has said. Although it would have a slight effect around the PCI cards, because in many cases, there is no circulation round there, so the heat from there will most likely rise upwards. I suppost you are right though four4875, but its best if you use it to your advantage (even if its small), rather than work against it.

stui_nz · May 14, 2003

Perhaps someone with a standard low intake - high outtake case could turn it upsidedown and see if there temp readings change..

DrSpanky · May 14, 2003

whats this your theory on heat riseing that was disoverd ages ago,

ZedBias · May 14, 2003

I have always belived in the "heat rises theory" thats why I have three fans at the top blowing out (Pushing hot air up and out) and two fans at the bottom suckin colder air in.

Seems to work fairly well.

WuChild · May 14, 2003

Cold air is more dense(molecules closer together) but the air itself does not have more mass unless you relate an equal volume of cold air to an equal volume of hot air.

A HUGE point about hot air in a computer case is that it rarely gets a chance to rise because air is being blown around constantly and mixed together.

Exhaust the hot air from the case, and you have cooler air to blow across heat sinks.

nerdlogic · May 14, 2003

This is interesting...what if you were to try killing any and all intake fans except one (or lower intake CFM) and keep your exhaust at full blast...with the air inside the case heating up as soon as it gets in, it'd be best to get it out of there ASAP and get some cooler air in.

ToledoSteel · May 14, 2003

While I don't think the "heat rises" theory is really applicable either, having a blowhole helps to increase airflow. The purpose being to keep the internal air of the case as close to the ambient external air as possible. Also having multiple fans alows you to run them at a lower speed (sound) and get the same results as fewer fans at higher speeds. There are also only so many places to put fans in a case. With drives and mobo trays, a limited amount of options exist. This is simply capitalizing on those options.

Splinter · May 15, 2003

Have your exhaust fans blowing out of the top of the case and the intake fans pulling cool air in at the bottom. My 2100+ runs at 32c idle and 36c full load!

Honest_Bob · May 15, 2003

Ooo, I have a good example. Ok so I have a nice Antec SX1040B. I have fans in all the holders (2 in the front 2 in the back) the front ones suck and the rear ones blow. I also put a nice Pabst 120mm fan in a blow hole in the top. I get better tempratures with it sucking air in than having it blow out.

my "heat rises theory"

four4875

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sandman001

Just Freeze It

Nolo31

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Diggrr

Underwater Senior Member

four4875

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Carnil

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wheatbix

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stui_nz

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DrSpanky

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ZedBias

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WuChild

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nerdlogic

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ToledoSteel

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Splinter

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Honest_Bob

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