an untested idea for getting a bit of extra cooling for a CPU

[m0ti]

hello,

I think anyone seeing this message is an OC'er of some sort, and so, like the rest of us, is after maximum CFM, and some of us, may just be interesting in the noise. I, myself, try to find a good balance between the two, which is what gave me the idea, which comes from... airplanes! yup, those great lumbering things that go soaring through (and crashing down from) our polluted skies.

So what's an airplane got to do with my HSF, you ask, and then smack yourself since it's so obvious. Air flow! How does a plane stay up? As most of us know, the air moving over the top of the wing moves faster than the air moving below the wing. This means that there is less air pressure above the wing than below the wing and the air there pushes the wing up and we get lift. How can this be used in a comp?

Normally, with a 60 mm fan what happens is that the air outside the heatsink is moving slower than the air exitting the heatsink (since the slower air just left the heatsink and lost even more speed to the air already there), and this SLOWS down the air exitting the heatsink! Not what we want!

So let's fix this. Imagine putting an oversized fan in your HSF. To be really outrageous, lets say its 120 mm. What happens here? Well, the air going through the heat sink is going through a torturous obstacle course when compared to the air not going through it. Thus, it's speed should be significantly less than that of the air outside the heatsink. Which means, that it's under more pressure than the air outside, and it gets pushed out/sucked out (if this confuses you think of blowing over a sheet of paper while holding one end. you blow out, pushing air out of the way, creating a short-lived vacuum which pulls the paper up).

Now, I don't think a mobo exists which'll let you put a 120 mm fan on a heatsink. But an 80 mm might fit, as might a 92 mm. You could also try using a quieter 60 mm, and stacking a larger sized fan on top of it. The air coming out of the heatsink should still be much slower than the air being pumped out by the larger fan.

it should also work for fans set to suck and to not to blow, as air'll get sucked in from further on the mobo (more surface area = lower average temp).

Anyways, let me know what ya think. Crazy enough to work?

 

[Technonut]

From what it appears, you came up with an idea for a fan adapter. Not to rain on your parade, but they are manufactured and available. You are also correct in thinking that the concept works better sucking air through a heatsink. (Especially on heatsinks with a shroud like the Alpha, HedgeHog, and Silver Mountain) You can see a couple of models Here, though there are less expensive models available.

I have been using the Silver Mountain and a 60 to 80mm adapter with very good results using the well designed Panaflo FBL Series Ring Cage Fan. It is interesting that the fan design was originally patented by Lemont Aircraft Corporation. Your thinking was right on the money.

 

[PlatinumGold]

techno

the way i read it, he means attach it w/o the adapter, just let the overflow provide negative pressure outside of the HS area so that air can exit the hs faster. the adapter would totally defeat the purpose of his idea.

o btw. i had a 92 mm fan on my WBK, worked well, no problems.

 

[m0ti]

Yeah, I was talking about running it without the adapater. The shroud seems at first glance the obvious solution. I think that without the shroud it may run better. And if you stack fans, it should almost definitely run better. I was hoping to set up a couple of quiet fans in this setup and hopefully get improved performance, since I've heard that the adapters don't always help too much (they give about the same performance, though they do lower the noise).

 

[Technonut]

I apologize if I read it incorrectly. It sounded like an adapter idea to me. I guess it would be like the idea I saw posted a couple of times where a 80 or 92mm fan grill is installed on the HS, and a larger fan attached to that with almost direct contact with the HS.

 

[m0ti]

That's ok. Yes, it does sound somewhat like that. I understand how you could read that as using a fan adapter, it's the most straight-forward approach. It'd be interesting to a benchmark of the whole thing, with the adapater and without, as well using a smaller, higher CFM, fan for scale. Unfortunately, I'm not gonna be able to do it for a couple of weeks until I finish up my exams =(

 

[WarCon]

In a prior thread (couple months ago) I had suggested a similar idea. But instead of mounting the center of the fan directly over the hsf, mount the much larger fan even with one side and hanging off the other. That way the fastest moving most turbulent air will be pouring down on the hsf. No one responded that they tested it (I watercool or I would).

I need a second system to play with..............

 

[clunk]

I've got a WBK38 on the way (along with a 1.4 (266) and several different case fans). I read your (or similar) post on using the offset 92mm fan and agree that this seems most promising. Just for kicks, I'm gonna start with the screaming 60mm stock fan and work my thru an 80mm then 92mm case fan and compare results.

The biggest problem tha I can see to the 92mm offset idea is that you are obviously cutting the CFM that goes directly on to the HS (i.e. a 40 CFM fan that is only half over the HS only gives 20 CFM cooling flow).

My money is currently on an 80mm fan centered on the HS (which is 75mm wide). I'll let y'all know what happens next week (when the schtuff should get here).

 

[kursplat]

actually a good way to create flow across the heat sink would be to encase it in a housing that had a cross flow design. two blow holes - one in \one out. use some thin wall PVC tubing. as few turns as possible. and you can use whatever fan size you want.
going to try it next case i hack-up

 

[m0ti]

Offsetting the larger fan could help, especially as airflow in a case is generally unbalanced, and one side of the HS may already have air flowing around it, in which case you'd want to offset the fan to the other side. Ideally, you'd want to hook up four fans (40 mm probably) to the sides of the HS sucking the hot air out of it, but it'd be pretty hard to hook 'em up, and since they'd probably all be spinning it out about the same RPM, this would cse a ton of noise as the HS would be vibrating like hell.