Passive side panel duct dropped my temps by 6C

pelikan

Diamond Member
Dec 28, 2002
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I am using an slk-800 with a 22dB, 25cfm 80mm fan. My load temp was 42C. I made this passive duct and now I'm at 36C under load.
I used a pvc drain pipe connector which is usually for connecting two lengths pvc landscape drain pipe; so its just a straight piece of pipe or tubing with a 4.5" outside diameter and about four or five inches long. They are $1.99 at home depot. I cut a hole in my side panel over my cpu and slid it up to the cpu fan. It just butts up to the outside corners of the fan, not covering it, and the other end sticks out the side of the case about 1/2". I cut the hole tight enough so that the duct stays there on its own when I slide it in.
Sorry I don't have pictures.
I tried different case fan arrangements. The case fans and my psu fan are the same 22dB, 25cfm, 80mm fans as I have on my slk-800.
All temps are under load:
No duct, one lower front intake, one upper rear exhaust: 42 cpu/ 26 mb
Duct, one lower front intake, one upper rear exhaust: 36 cpu/ 28 mb
Duct, one lower front exhaust, one upper rear exhaust: 32 cpu/ 31 mb
Duct, one lower front intake, one lower rear exhaust, one upper rear exhaust: 36 cpu/ 25 mb **This was the arrangement I stuck with.
 

BlueWeasel

Lifer
Jun 2, 2000
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Significant decrease in temps you have there. I am interested in doing this once my SK-7+fan arrives from SVC. I may be reading it wrong, but do you have the CPU fan pulling air away from the HS into the duct, and then a rear exhaust fan is attached to the other end of the duct?

Pics? :)
 

pelikan

Diamond Member
Dec 28, 2002
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The fan is blowing onto the heatsink like usual. The duct is a straight tube that goes straight out the side panel of the case. There is no fan on the duct, it doesn't need one.
 

BlueWeasel

Lifer
Jun 2, 2000
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Not meaning to thread crap in any means, but did you try reversing the HSF so that air is being pulled away from the CPU and into the duct? It just seems to me that would be the way to go as the difference in temperature of the air in the duct and the motherboard temperature would be negligible.

I'll probably try this once I get my SK-7 and fan ordered, and I'll let you know how it goes.
 

pelikan

Diamond Member
Dec 28, 2002
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That's not a thread crap. I appreciate the idea; I havn't tried that yet.
I do think the reason this duct has worked so well is that it pulls cooler air from outside the case. But who knows? I'll turn the fan around and post my results. It would be nice to get the hot air out directly.
 

pelikan

Diamond Member
Dec 28, 2002
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Okay, I turned the cpu fan around so it blows out the duct. My temps went to: 52C cpu/ 26C mb.
I thought it would work better than that.
 

BlueWeasel

Lifer
Jun 2, 2000
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Originally posted by: pelikan
Okay, I turned the cpu fan around so it blows out the duct. My temps went to: 52C cpu/ 26C mb.
I thought it would work better than that.

Wow...I am suprised about the difference in temperatures. However, the more I think about it, it makes sense with the way you had it to begin with. All of the current AMD cooling solutions pretty much are designed for the airflow to be going toward the HS. In your case, you are pulling air onto the heatsink that has not been stagnant in the case, and therefore should have a much lower temperature as compared to the air inside the case. Obviously, your lower temps support this. :)

One of the best P3 coolers is the Alpha PEP66, and I think it was designed for the fan to pull the air off the HS. That's the way I run it on my P3 1ghz@1.33 and my temps are lower compared to having the fan blow onto the heatsink. It would be interesting to see how much improvement I might get by installing a duct on that system.

Thanks for posting the various results....
 

pelikan

Diamond Member
Dec 28, 2002
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It sure is interesting, isn't it? Air flow dynamics...
You mentioned P3 heatsink that is designed to pull air off the heatsink. Makes me think of one of Dell's solutions that pulls air off a passive heatsink and right out the rear 92mm exhaust fan.
My experiments today and yesterday have shown me that trying everything possible is the best approach. Because in my case, I just don't know what to expect.
 

BlueWeasel

Lifer
Jun 2, 2000
15,940
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Originally posted by: pelikan
My experiments today and yesterday have shown me that trying everything possible is the best approach. Because in my case, I just don't know what to expect.

Amen. :)

BTW, what 80mm fan are you using with the SLK800?

I am looking for fan recommendations to go with my SK-7 and SVC is out of stock of the Panaflows. I have heard negative things regarding the Vantec Stealth fans and am considering getting one of the Enermax Whisper fans.
 

pelikan

Diamond Member
Dec 28, 2002
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I'm using NMB fans from a guy at AMBMB Forums. They are cheap, work great and he ships fast; which is the good part. The bad part is you can hear the bearings. So while they are pretty quiet, the sound that does come out of them includes a high-pitched bearing noise which I don't like. I'm trying to decide now what fans to replace them with. They will definately be sleeve bearing. There are panaflos for $4.50 here. Or I may try the 92mm Zalmans at SVC- the ones with the resistor that runs them at 5V and puts out 38cfm at 20dB. But before I buy I'm going to try 7V-ing some 28dB sleeve bearing fans I have, and various fan combos. I may come up with something that will satisfy.
 

THUGSROOK

Elite Member
Feb 3, 2001
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i can verify this works. (air coming in side panel)

ive been running this type of "mod" for 2 years already :)