big or small case for better cooling?

lemons · Post by **lemons** » Sat Dec 02, 2006 3:41 pm

Hi

I think it is generally assumed/known that larger cases are better for cooling. Is it possible that someone could explain why? Simply, but scientifically. The more I think about it, the more confused I get.

The way I understand it is, that in a larger case there is more air and the components are not close enough to heat each other up.

This makes some sense, but in a more compact case like stonyc's TJ-08, the cpu heatsink and gfx card must benefit form having direct airflow from the front intake. I also would have thought that airflow would be more efficient in a small case. Therefore a larger case would need more fans.

hehe, Sometimes my ignorance amazes me.

Bluefront · Post by **Bluefront** » Sat Dec 02, 2006 4:43 pm

IMHO.....There's no definite winner here. Each size case has advantages. As long as the case is large enough to comfortably hold your PSU and a big enough CPU heatsink, each size can be equally quiet.

pyogenes · Post by **pyogenes** » Sat Dec 02, 2006 5:24 pm

Air can't hold much heat, so even doubling the volume of air would do little to reduce the temps. Specific heat capacity is only about 29 J/(mol*C). An average case would hold around 2 mol of air so it only takes 58W of heat production to raise case temps by 1 C/sec. Doubling the amount of air would only halve that rate. Even at that slower rate, without airflow a case would raise 100C in under 3.5 minutes and well under a minute for an overclocked quad core system with a 8800GTX video card under full load even in a case twice the size of the P180. And that's why we need airflow.

The main cooling advantages of larger cases are the following:
1. Bigger heat sinks can be used (better moving the heat to the air)
2. Bigger fans can be used (better airflow)

Shadowknight · Post by **Shadowknight** » Sat Dec 02, 2006 11:01 pm

With a bigger case, you can put the hard drives, and possibly the optical drives, farther away from the CPU/heatsink and PSU, keeping them from getting heated up from those components. Also, it MAY help the PSU keep from ramping up if it's further away from the CPU than in a smaller case. But that's just an unscientific guess.

pyogenes · Post by **pyogenes** » Sun Dec 03, 2006 7:14 am

That would only be true if you had a separate exhaust for those hard drives that keeps the hot air from reaching those other components. Heat doesn't just disappear due to distance.

lemons · Post by **lemons** » Sun Dec 03, 2006 8:44 am

ahh, ok, so bigger cases are not significantly "better" for cooling, just "easier" because of the extra space to work with.

makes sense, thanks.

RAFH · Post by **RAFH** » Sun Dec 03, 2006 10:28 am

pyogenes wrote:Air can't hold much heat, so even doubling the volume of air would do little to reduce the temps. Specific heat capacity is only about 29 J/(mol*C). An average case would hold around 2 mol of air so it only takes 58W of heat production to raise case temps by 1 C/sec. Doubling the amount of air would only halve that rate. Even at that slower rate, without airflow a case would raise 100C in under 3.5 minutes and well under a minute for an overclocked quad core system with a 8800GTX video card under full load even in a case twice the size of the P180. And that's why we need airflow.

The main cooling advantages of larger cases are the following:
1. Bigger heat sinks can be used (better moving the heat to the air)
2. Bigger fans can be used (better airflow)

I'd add
3. Larger cross-sectional area for whatever air flow channels are developed so less friction and lower air speed for a given flow rate, means less noise and the fans don't have to work as hard.

jaganath · Post by **jaganath** » Sun Dec 03, 2006 10:51 am

On the downside, large cases are usually eyesores and in a small room take up a lot of valuable space; so basically the smallest case that provides adequate cooling is best.

RAFH · Post by **RAFH** » Mon Dec 04, 2006 8:32 pm

That is only applicable to people who don't make their computers the center of their lives and worship them in which case the bigger and more impressive, the better. Best of all is a case so big you have to demolish a wall to get it into the room! Or a case you can live in. In a small corner off to the side or up in a loft with the Antimatter MegaWatt Power Supply.

mbetea · Post by **mbetea** » Mon Dec 04, 2006 10:20 pm

From my limited experience I would say it's not really the size of the case, but how it's setup. For a while I ran an ATX Tyan board with dual Opteron 244's, 3 HDDs, video and sound card in a Sonata. The position of the sockets in relation to the fans in the case were so that I was able to run the cpus passive using Alpha coolers.

So I think it comes down to planning and some guess work on how the hardware you select will sit inside the case you select. Because on the flip side, when I got rid of the Opterons for an x2 I found a lot of the newer boards position the graphics card slot lower on the motherboard than the Tyan did. So, the video card ran hotter because it got no airflow at all from the front fan of the Sonata.

crypt0r · Post by **crypt0r** » Sun Dec 10, 2006 6:45 am

I'd add
3. Larger cross-sectional area for whatever air flow channels are developed so less friction and lower air speed for a given flow rate, means less noise and the fans don't have to work as hard.

From what I understand, more friction (turbulence) and velocity equals more cooling, which allows you to run slower / fewer fans, yielding less noise. That's why we typically mount fans to our heatsinks, instead of in free air an inch or more away from them.

I've been daydreaming for quite some time about constructing a custom case in which most of the intake airflow goes as directly as possible to the components that require the most cooling.

Buying a P180 is cheaper than construction. Keeping my SLK3700AMB is cheaper than buying a P180. =P

Back to daydreaming...

RAFH · Post by **RAFH** » Sun Dec 10, 2006 3:34 pm

Yah, you want as much air crossing your cooling components as possible, a given volume of air will absorb only so much heat for each degree of temperature delta, so more air means more heat absorption. But high air velocities are what makes noise. Especially high air velocities across surfaces and even more so over edges which will create turbulence. Friction and turbulence make noise. So for cooling you want lots of air, for quiet you want low velocities, that means large cross-sectional areas. Its a simple equation, you want volume for cooling and low speed for quiet, V = AS, for low speeds you have to have large areas.

Turbulence on the cooling surfaces is good because it exposes as much of the air moving by the surface to it as possible. If you don't have some local turbulence you will get laminar flow which limits the air-surface contact. In other words, any air not in the contact lamina will not absorb heat so is wasted. That's why your cooling fins should have dimples on them or other such local turbulence inducing features. But on the large scale and wherever the air is not in contact with cooling surfaces you do want laminar flow because it takes the least energy and produces the least noise.

jaganath · Post by **jaganath** » Sun Dec 10, 2006 4:06 pm

Good summary RAFH.