My current CPU HS has an 80mm fan sitting on top (as with most standard HS's, Zalmans excluded), but looking at the airflow through my case, and particularly with my exhaust fan in close proximity at the back, it seems to be "fighting" the natural air flow inside the PC. i.e. it is blowing perpendicular to it.

One thought I had was to mount the fan on the right side of the HS, blowing across the HS fins towards the exhaust fan.

Has anybody had any success with this? Has it helped CPU temps at all? The difficulty is to mount it properly, and I have my doubts it would be pushing as much air over the HS as the standard configuration.


pangit

I would try reversing the direction of the fan, making it suck off the heatsink instead of blowing, thus allowing the exhaust to remove the air immediately.

pangit, you're idea isn't a bad one. There are some heatsinks specifically designed to blow that way. (I know Aopen makes some, I'm sure there are others. They're used in 2/4U rackmounts alot)

The problem with doing to your existing HS is that if the HS isn't at least 80mm tall alot of the air the fan blows will miss it. You could get creative and build a little duct/shroud thing to force all the air over the HS. You'd want the air to be made to go down the little valley's between the fins (that's what you meant by across, right?)

As an example of what I'm talking about take a look at this:

Rusty's Quiet In-Desk PC

Same idea, only with a Zalman flower and a 120mm fan. If I had to do it over again I would have reshaped that duct, so that the taper ended at the side of the heatsink nearest the fan, with a straight tube-like extension covering the top and sides of the HS. I think that would have improved performance by forcing the air into better contact with the fins.

Thanks for the tips guys. Rusty, does your fan blow onto the HS or exhaust it? Yes, I meant the fan would blow air through the fins, but as my HS is only about 40mm tall half of the airflow would be wasted I guess.

It certainly might be worth trying to reverse the fan and seeing what effect that has.

In my case the 120mm was exhausting the air.

Reversing the flow might help some, but it's still working perpendicular to the rest of your airflow. You could reverse it, and then duct the cpu fan out the back. That way the warm air coming off the heatsink won't be recirculated inside the case.

In fact currently I have mine ducted in from the outside (with a cardboard duct coming from a hole in the side panel directly in line with the CPU), so it is blowing fresh external air directly onto the CPU HS.

But I'm wondering if your solution Rusty, doing exactly the opposite, would improve things. One reservation I have is that the airflow over the CPU will be warmer as it uses warm internal air, even though the air in the case is probably cooler overall! In an ideal world you would want the CPU air intake and exhaust to be completely external, to keep the inside of the case (and other components) as cool as possible. But I don't think I could do that without major case surgery and a completely different HS design.

BTW, I'm well impressed with your in-desk PC project, it looks great (although not ideal for LAN parties )

Pangit,
Did you finally experimented any of the proposed solutions (reverse flow or small cover for the "Across" solution?).
I have this issue of cpu fan competing against big perpendicular sucking flow from 120 exhaust fan.
Plus the 80 cpu fan is on top of a 60-80 adapter, so it really came in the way of the 120 fan.
Any thoughts?

Just found this thread when it bounced to the top today.

Rusty, that's some great duct work! I'm a bit worried about that big passive heatsink on the northbridge that's expecting to be cooled by the flow of air from the CPU HSF...

One problem with exhausting air off a CPU HS is that you're "cooling" it with air already warmed inside the case. That can be several degrees warmer than the outside air.

Thanks sbabb. Yeah, if I had it to do over again I'd at least try it with that fan reversed. There would be some issues with the PSU exhaust, and the reduction in airflow over the HDD, but the CPU would definitely be cooler.

The northbridge cooling, at least with that chipset, was really a non-issue. It would run just fine with no HS on the chip at all. Even with nearly zero airflow over it that HS never even feels warmer than ambient.

.g

FLD, I haven't done much experimenting yet but I've formulated a few ideas. I don't think I'm going to try the perpendicular fan as I don't think it would work with my current HS, and I don't want to buy a new one especially. My current idea is to duct/shroud the intake/exhaust air for the CPU to keep it completely separate from the rest of the case (we're talking serious ghetto here, note the "on the cheap" comment on my web page!! )

There are a few pictures of my current setup here and you can see I've already got square cardboard intake duct. I'm planning to replace it with an 80mm round cardboard tube, which should interfere with the case exhaust fan less than the square one (the duct sits quite close to the exhaust fan, although you can't see it from the photos with the side panel off!)

I'm also planning on constructing a cardboard shroud similar to Spydercat's (his first one) to exhaust all the CPU air through the PSU. I've already opened up the bottom of the PSU completely just above the CPU (as well as replacing that nasty Titan with a Panaflo) and I've got a temp controlled Panaflo exhausting the PSU. This should keep the internal case temp down, so I can slow the intake and exhaust fans down and still keep the other components cool.

The idea is to separate the cooling into two distinct airflows, so they are not competing with each other: a low airflow going through the case cooling the HDDs, graphics card ane memory etc, and a more concentrated temp controlled (and probably higher) airflow cooling the CPU and PSU.

That's the theory anyway. I won't have it done for a while yet as I've got another "summer" hobby on the go at the moment, which is taking up most of my spare time while the weather is still good!

But I'll be reporting my findings back here when I've done this, and see what it does to my PC temps/noise!!

Thx Pangit! Nice page you have! I do agree the cheapo way is by far the most interesting one (as I think most SPCR friends do)!

Re. CPU HS, sorry you did not try the perpendicular way (we are talking CPU cooling here )... I am really tempted...

Re. ducting the side intake, you may want to replace cardboard by a section of soda plastic bottle. These (at least in Europe) are exactly 80mm in diameter, easy to cut/ adjust, and transparent!

I currently have almost an entire (empty) 1 liter coke plastic bottle as internal ducting, taking fresh air from lower front intake up to my CPU fan.
(I have pics if you like, but I am not sure how to post them as I have no site).

I might try the coke bottle - I'll probably try both and use the one that resonates the least. The trouble with this kind of duct is that it will amplify the sound of the fan, so I'll have to see which one is best.

Once I've move my HDDs down in front of the fan I was thinking of using another bit of ducting to direct air onto the graphics card. I'd be interested to see your photos if you can find somewhere to host them (surely your ISP gives you some free webspace?)

This may not apply to you EU guys, but a handy tip for anyone in the states is that the Pringles potato chip cans are exactly 80mm in diameter.

I am sooo not worthy Rusty.
I've been planning a CPU duct (made from household materials) for ages and that would be perfect.
I'm guessing using cardboard will be safe - temps wouldn;t pass 60C - hopefully they won;t come anywhere near it.

DonP.

PS. We have Pringles in Europe - and tomorrow I'll check if the EU cans are the same diameter.

Always willing to help.

I've been using a "Pringles Duct" on one of my machines for several months now without a problem. The only part that requires creativity is how to make that attachments at eack end. Through much scientific study I have decided that duct tape will work just fine.

Duct tape and Pringles tubes, it gets better all the time! - I love it! Where would we be without good old duct tape? (it's practically holding my PC together now!)

The motto always holds true, "If you can't fix it, Duct it"

Service offerred - Supply Pringles, I will empty them 4 u

and deprive my little sister of her job as garbadge disposal?

my mouth is bigger

Ok, I finally found a way to publish some pics...
So here it is, my famous Plastic coke bottle ducting:




This thing is taking air from above the HDD and safely convey it up to the CPU fan. Took me almost 2 hours ( and 3 bottles) to find out how to cut it so it would fit closely the edges of the fan, while aiming at the HDD...
Then of course it is "sealed" with regular scotch tape.
Works fine from a pure CPU-cooling standpoint, but:
- badly interfers with 120mm exhaust fan.
- kind of reduces airflow
- resonates badly (but I find out most of the noise was in fact coming from the 80 -> 60 adapter).
- made further modding a pain has I could not reach behind it.

I was still happy about it for a month, until I decided to mod the CPU rad itself... Stay tuned!

Like it FLD, . Although it's quite difficult to see from such a small picture. Do you have anything bigger?

I'm thinking of doing a similar thing once I drop my HDDs down near the intake fan - but duct air from the HDDs onto the graphics card, as my CPU air comes from the side of the case. That way I can get rid of my whiny little fan on my Radeon.

I have the same problem with my duct interfering with my exhuast fan. Unfortunately with the design of ATX systems there isn't much you can do about it.

I have found a heavy 80mm cardboard tube which may dampen the sound more than a coke bottle or Pringles tube, but I haven't tested it yet. You are always going to get some resonance, so it's the price to pay for ducting I suppose.

Let us know about your CPU rad mod, I'm intrigued now!

Sorry for the small pics, I agree it's difficult to check details...
Here is another shot, but could not make it bigger... Will have to rework this tonight!



Basically, the top of the bottle makes the top of the duct: I cut the bottleneck, but kept the rounded part, and close the hole with scotch tape.

Re. Radean whiny fan, you might want to look at my post here re. GF4 TI 4200 80mm cooling:
http://forums.silentpcreview.com/viewto ... highlight=

Cheers!

loks kind of obtrusive?

or it might be just too small. i dunno.

It indeed comes very close to the exhaust fan, but that's one of the caveat of my Mobo.
On the other end, it was a good way for me to stop exhaust and cpu fans to interfer.
Eventually, I got rid of this duct for this and other reasons: it bloked too much volume in the case, resonates a bit, not to mention the fact that such a long duct really slows the air, forcing me to rev the CPU fan up.
Was worth a try anyway, and a lot of fun to build too... so I thought I would share the story with you .

Ok, I did it: tested the "cpu fan perpendicular to mobo way"! Thanks Pangit for the idea and encouragements!

Objective:
- Here is the initial set up: what matter here is the cpu fan and Heatsink: Taisol Aqua HS, with 60mm fan replaced by 80mm Noiseblocker S4 on 60->80 adpater:



- As you can see, the cpu is located pretty close to the rear of the case, so that the 120 exhaust fan and the 80 cpu fan are competing against eachother. This is bad because it requires to have both fans rev higher (=louder) than needed to get the same flow.



- To solve this competition issue, I already tried ducting (see above in this trend), but was not happy with it (resonates, obstrusive vs exhaust fan, and... well, uh... ugly!)
So my objective was to somehow have the 2 fans (cpu and exhaust) blowing in the same direction, ie toward the rear exhaust hole (from right to left on the pic).


Preparation
First, I started with some modding of the heatsink:
My Athlon 1.4 ("Toasterbird") has a Taisol Aqua heatsink (80x60mm Al/Cu base, Al fins), with a 80 mm Noiseblocker S4 blowing thru a 80->60 adapter.



The Taisol Aqua HS was designed to have a fan facing it, not being perpedicular to it. So I decided to help it a little bit with a popular mod of the rad fins.
The idea is to allow for more space between the rad fins, by bending them toward the outer of the rad. Bending each of the 120 Aluminium fins without breaking any is a bit touchy... and doing it leaving the HS on the cpu is not recommended... But somehow both the fins and the cpu seemed to survive it.
The result is an increase in the height of the heatsink, which is nos 80X90mm, versus its initial 80X60mm dimensions (stock fan was a 60mm whiny one).
The benefit is much more space between the fins, allowing for more air to pass thru more easily.




Positioning the cpu fan
I used some strong electric wire to suspend the fan to the case bar. This is as cheap as can be, but actually is very handy to quickly experiment several orientations ( both vertically and horizontally speaking).



First, to test the modded rad and the effect of getting rid of the 80-60 adapter, I started by hanging the fan just face to face with the rad, almost in his standard position.
Results:
- noise improved radically: I guess due to the fact that air is no more smashed thru the adapter and against the HS. Also the fan does not generates any more vibrations that resonate in the HS).
- temperature did not moved a bit, so I decided to carry on the test.

So here is the real test: I started gradually turning the cpu fan, until his final position right of the HS, in a almost perpendicular angle to the mobo.
Results:
- as the fan was moving to the right, cpu fan rpm went up, showing that there was less and less competition with the exhaust 120 fan,
- cpu temperature went down 3 degrees (idle: 51 to 48, load: 57 to 55), from the initial position to the perpendicular position. I was happy with this but decided to "re-invest" this temperature benefit in reducing both fans revs.
- the MAJOR improvement is that it allowed me to decrease the cpu S4 fan speed from 2700 rpm down to 2290 rpm: made a huge noise improvement because this brought the fan back to its "quiet" range of operation.
- I was able to also reduce exhaust fan speed ( from 2100 to 1600 rpm), reducing engine and turbulence noise. Due to reduced competition, note that this did not impact case temperature!
- Testing several angles/positions also confirmed that moving the fan away from the HS certainly reduced turbulences, but there is a compromise here when the fan is too far from the HS to ensure proper cooling.

Here is my final setup, with the 80mm cpu fan perpendicular to the mobo. Note that it is blowing slightly upward for a couple of reasons:
1/ when the fan is blowing, air pressure makes it move backward a bit, so its working position is actually more vertical;
2/ this position allows some fresh air to be pushed into the PSU fan, reducing its need for revs, and so cutting PSU noise as well.



Another view more from the front of the case: no doubt: the 2 fans are blowing in the same direction!


So overall, it works, and yes, it is much more silent than before!
I now plan to take it a bit further (too far?) by applying a second round of fin bending to the HS. But i promise this time I will remove the HS from the CPU for the extra bending... and apply some Artic ceramique as well...

That's a great experiment FLD! I didn't think it would make so much difference, but you showed that it does.

It makes sense, as the CPU fan should make less noise if there is less resistance in front of it. But I'm pleased to see you achieved a temp drop too, even though the HS fins aren't tall enough to reach to the top of the fan. Imagine what it would do for a HS/fan designed to operate that way! (I haven't seen any, but I believe they exist).

One thing to be careful of, if you bend the fins outwards, it could cause the HS base to bend slightly too (I'm just guessing here), so the mating surface is no longer totally flat (it would probably be too small to see). The solution would be to lap it after bending, so you get a nice flat base again!

This is such a crap argument in my opinion. The CPU is by far the LARGEST heat producer in the system. Nothing else even comes close! What exactly is going to heat up the air inside the case when you.. remove the #1 heat producer from the equation?

Once you've forced the ~100w consuming CPU (modern p4 3.2ghz or better, or Athlon 3200+) to dump its heat outside the case-- via ducting or whatever-- then keeping the case air near ambient is fairly trivial, IMO.. this can be accomplished with probably a single 120mm low-rpm fan. Or possibly even one of the nicer 120mm fan powersupplies by itself (Seasonic Tornado, etc). Unless you have a 5-drive 10,000 RPM SCSI array inside your PC or something crazy like that..

I suppose if you were really hardcore you could duct air in from the front of the case, over the CPU, and duct it back out of the case. That would be one gimongous duct, though.