Going to add foam to dampen noise. How to minimize heat?

Keitaro · Post by **Keitaro** » Sun Apr 27, 2003 9:32 am

How can i minimize heat after i add foam to dampen the noise? I got two front bezel fans, the CPU fan, and a dual fan power supply. Is this enough to keep good airflow?

JEN · Post by **JEN** » Sun Apr 27, 2003 11:56 am

I'm no expert, so don't take my word for it. From what I have learnt so far, it is better to have more exhaust fans than intake fans. The intakes can be fanless as the exhaust fans will pull air throught the intakes and exhaust hot air back out!

Don't shoot me if I'm completely wrong guys

powergyoza · Post by **powergyoza** » Sun Apr 27, 2003 3:05 pm

Keitaro, yes in general good airflow will minimize the temp rise from a dampening a case.

JEN, I agree with your POV. Intake fans are mostly for a) keeping the dust out when moving more air than the exhausts and b) targeting hotspots with cool air.

Cheers!

Bluefront · Post by **Bluefront** » Mon Apr 28, 2003 2:42 am

Well I have a difficult time with this subject. The case itself does not radiate much heat. Similar steel and aluminum cases with the same fans run about the same temps. So if the airflow over the board remains the same, why should the temps go up if you apply acoustic dampening to the case sides?

I have stuffed my antec2600 with all sorts of acoustic dampening....the temps are the same as when it was stock. Of course if the dampening restricts airflow over the board, the temps will suffer. Check your temps at various points before and after the foam mods...that's the only way to know for sure.

JEN · Post by **JEN** » Mon Apr 28, 2003 2:51 am

Correct me if I'm wrong. The temperatures would definately go up if you relied on the tiny holes in the case for cooling and you added foam. As the foam would block all the holes! However, if you already have all the tiny holes covered with good air flow, adding foam to the case should not have any temperature effect as long as you leave the inlet and exhausts uncovered.

Am I right by saying that?

Gekkani · Post by **Gekkani** » Mon Apr 28, 2003 4:27 am

JEN wrote:Correct me if I'm wrong. The temperatures would definately go up if you relied on the tiny holes in the case for cooling and you added foam. As the foam would block all the holes! However, if you already have all the tiny holes covered with good air flow, adding foam to the case should not have any temperature effect as long as you leave the inlet and exhausts uncovered.

Am I right by saying that?

Yes... In theory. But as Bluefront says, temps usually dont rise due to add foam... WHEN a correct airflow has been stablished.

For example i have my case dampening with foam, 2.4cm thick (sides, front, rear, up... even at the back of the mobo) and I have lower temps with the case closed than with the case open.

jafb2000 · Post by **jafb2000** » Thu May 01, 2003 3:40 pm

It is true that soundproofing works by converting energy that is in
the form of noise into heat, however it's worth realising it's tiny.

Noise generators in a PC are fans & motors, usually motors if the
cooling paths are clear of obstruction immediate to fan blades.

Those fans & motors add up to 10W at most even on a large server,
most of that energy being emitted in the form of heat, not noise. The
noise energy is probably 10% of that at most or about 1W.

Thus soundproofing your case doesn't make it hotter, unless you
disrupt airflow or physically clog air inlet or outlet holes in the case.

The higher the wattage of your fans, and the greater the number,
the better it is usually to run them in extract mode. This is because
the fan dissipates heat according to the wattage marked on it, which
can be 1W, 2W or 5-7W for typical PC case fans. If you have 10 5W
fans on the inlet, you are pre-heating the air with 50W of heat. If the
fans conversely are on the outlet, that heating merely elevates air
that has already been extracted from the case, and is only then a
problem if the machine can materially increase surrounding ambient.

Conversely, fans run in extract-mode extract hotter air than they would
if used as intake fans - and the hotter the air, the shorter the life of the
bearings in the fan. This is where PSU fans should always be the best,
yet invariably aren't and thus most PSU failures are fan related.

So there are positives & negatives to either use.

Fan noise can be reduced in cases by 2 things:
o Insetting fans away from rear panels, and lining that short duct with
soundproofing material - both mass & acoustic foam (QuietPC 3-pk)
o Forcing outlet air to deviate 90-degrees, ideally 180-degrees
----- each 180-degree turn in airflow reduces noise by 6dB(A)
----- should also be realise it reduces airflow by introducing static pressure

Some cases, mainly very expensive Compaq servers have air holes in
strategic locations - so cool environment air is drawn in at these places
to reduce spot temperatures in the immediate area. Generally these are
obvious, as opposed to the hole-afterthought of some case designs

--
Dorothy Bradbury
www.stores.ebay.co.uk/panaflofan

jverheul · Post by **jverheul** » Thu May 01, 2003 4:13 pm

That is some good information Dorothy. However.......

I doubt that all the 5W from a fan is transfered as heat to the air moving past it. Even a heat gun is not 100% efficient, and it is designed to heat the air passing through it. Most of that power goes to moving the air, not heating it. Most fans are plastic, which is not very thermally conductive. The part that does get hot is not very exposed to the airflow. Moving air can conduct heat, trapped air is an excellent insulator. The DeltaT across an intake fan of a PC is likely negligible (deltaT << 1C), even if you put the 10 fans in series. If the fans are parallel then we would want to consider the power per unit volume (cubic foot, liter...). Adding more parallel fans would not change this value.

Do you have data to prove me wrong?

Has anybody ever noticed that an intake fan was warm after running? I'll check mine tonight.

JV

jafb2000 · Post by **jafb2000** » Fri May 02, 2003 2:11 am

Sorry, yes, the post was done late at night - *smile*

o Fans unlike chips turn most energy into rotational kinetic energy
---- thus 50W of fans don't create 50W of heat :-)
---- had racks on my mind where the # of fans can be 50-500W of heat
o Intake fans do heat the air slightly, vs extract fans which don't
---- for PCs this is a mute point since it's minor versus PC contents

The benefit of fans in intake mode is that they are exposed to lower
temperature air than in extract mode and so last longer. For some fans
this can be quite significant - their lubrication is only spec'd for a tight
range such as 20-35oC and above/below that they perform poorly.

Conversely if you run fans in the 0-5oC environment, they are much
better off in extract mode because lubrication otherwise can be poor.

The arguments for fans as intake are:
o Exposed to cooler ambient air - so last longer
o Allow point cooling of objects near to them - eg, HD cages
o Create opportunity for positive case pressure - so dust reduced /a bit/

The argument for fans as exhaust are:
o Fan heating itself doesn't contribute to the cooled environment
---- altho this is minimal for PCs for racks it does add up re 480+ fans
o Hot air extraction can be more efficient re location
---- air-inlet location can be distributed next to hot components
---- air-outlet location can be next to particular hot air sources (CPUs)
------- removing hot air immediately from CPU coolers vs recirculate it

The main thing is ensuring your intake c/sectional area is large enough
right through to the outside, often they are not re small plastic slot.

I'll wake up shortly, bear with me :-)))

Zhentar · Post by **Zhentar** » Fri May 02, 2003 7:46 am

the thing to remember is how much airflow 50 W of fans would make- if you had that much airflow, 50 W of heat would be negligable. and you'd be at the wrong web site right now