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Quiet PCs, Ducting Air from Case Fan to Heatsink?
Milo_Mindbender asks: "While listening to the whine of my heatsink fan I was wondering. It seems like a good way to get quiet cooling for the CPU would be to mount a fan in the back of my case and run a duct of some kind (folded sheet metal or some kind of hose) from the back of the fan directly onto the top of a fan-less CPU heatsink. You should be able to get the same amount of airflow with a large slow (quiet) case fan as you do with a little noisy cpu fan...and the air being blown onto the heatsink would be cooler as well. This seems like a fairly obvious idea so I'm wondering if there's some reason why it wouldn't work, or if anyone has tried it and could tell us how it turned out." Yeah, but what about the heat in the rest of the system? Depending on the size of your enclosure (and what's in it), you may or may not need more than one fan. Has anyone tried something like this and can comment on how well it worked?
Speaking of aircompressors, careful when blowing out computers. If you spin the little fans beyond their normal speed you can kill the little sleeve bearings... I've did this a couple times years ago before I learned better. If you must clean the fan, stop it from spinning with a screwdriver or something. Also, make sure you have a water trap on your air line or you can end up spraying a fine mist of water all over the inside of your computer.
Back on topic, lots of commercial machines / servers have this ducting. My compaq servers had it over the ram and CPU's and rather than blowing in from the out side, it sucked the air out. Your big heat generators are your RAM, CPU, and diskdrives.
My homebrew tower actually has one big-mother fan that takes up 3 5-1/4" drive bay slots (sits in the front of the opening) to cool the drives behind it in addition to the 2 other case fans, and power supply fans. With dual processors, 2G ram, 4 36G 10Krpm scsi drives, it would get bloody hot in there without all those fans.
While I haven't played with it much, the lmsensors package on linux can tell you temps of various things on the motherboard which could be useful in playing with cooling.
In trying to keep the noise out of the house, I built a cabinet in the garage for my servers and ran a duct from my central airconditioner to the cabinet. I run the furnace fan continually and the thermostat is never set over 75, so it keeps things nice (note that I have a thermostat controlled damper that shuts the vent when the heat kicks on.) I'm mentioning this because you have to keep in mind that you can have that you can have nice airflow in your case, but if your machines in a 95 degree room it's not gonna do much good.