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| Thread ID: 60921 | 2005-08-18 04:47:00 | Airflow over a CPU | chiefnz (545) | Press F1 |
| Post ID | Timestamp | Content | User | ||
| 382013 | 2005-08-18 04:47:00 | Ok simple question... Would it be better for the fan on my CPU to EXTRACT the hot air from the CPU or would it be better if the fan BLEW cool air over the heatsink and CPU? cheers chiefnz |
chiefnz (545) | ||
| 382014 | 2005-08-18 04:58:00 | They normally blow air over the heatsink / CPU | CYaBro (73) | ||
| 382015 | 2005-08-18 05:00:00 | What was it doing origionally?? I dont think it realy matters that much. | Rob99 (151) | ||
| 382016 | 2005-08-18 05:57:00 | Blow onto it. And even better - a side case fan that blows onto that as well. Keeps mine nice and cool.. :) |
pctek (84) | ||
| 382017 | 2005-08-18 06:01:00 | I'm going to be pedantic again . Air doesn't directly remove heat from the CPU itself . Heat flows from the CPU to the "heatsink" (unless something is seriously wrong ;)) by conduction . The closer the physical contact of the two, the better . That's why we use compounds and tapes . Then we have to transfer heat from the "heatsink" to the air flowing through its fins . The more air moving through the fins the better . The faster air flows through the fins the better, subject to some turbulence/cavitation problems . The cooler the air moving through the fins the better . A "heat sink" doesn't sink heat . If it did, it and the CPU would just get hotter and hotter until something melted . It's a heat exchanger . We use the atmosphere as a "heat sink" . My computer heats Christchurch . A "CPU fan" which sucks airs then blows it through the HS fins will nominally shift the same volume of air through it as one which sucks it through the HS . But it will move a greater mass of air, because the air it moves will expand as it is heated in its passage through the HS . Against that, it is working against a higher back pressure . But the "suck" fan is pulling the air through a similar frictional resistance, then discharging to a nil back pressure . The differences probably aren't very significant . Terry might do the maths . ;) My inclination is for the "blow" system . It should be possible to arrange for the coolest possible air to be fed to the fan inlet (some cases I've seen have had ducting to do this) . The other way relies on air crossing the surface of the motherboard (over and around other warmish components) before it is sucked into the fins so is not the coolest possible . The most important thing is good circulation in the case . Air should come in, do the best it can, and then leave as quickly as possible after being heated . |
Graham L (2) | ||
| 382018 | 2005-08-18 06:25:00 | I had a stock Intel heatsink and fan, over the last few days I've noticed that the fan speed has been dropping below 1700rpm (comes up in red in the system BIOS) I became a bit concerned as the CPU is over-clocked by 600MHz to 3.4GHz, I haven't had any problems though with the over-clock. I have now replaced the stock heatsink and fan with a Titan heatsink and fan (see here) (www.dse.co.nz ) I removed this heatsink and fan because it was a bit loud but with the PSU I have as well as the X800XT graphics card you can barely tell the difference anyway. I was initially going to turn the fan around so that it blows air over the heatsink... the original way it was set was to suck air away from the heatsink. I googled a bit and the main train of thought is that it depends on the manufacturer... some recommend sucking hot air off the CPU and heatsink and others recommend blowing air onto the heatsink and CPU... this depends on the design of the heatsink and fan. cheers chiefnz |
chiefnz (545) | ||
| 382019 | 2005-08-18 07:56:00 | every CPU and VGA cooler I've ever seen blows air onto the heatsink. Rear case fans and PSU fans should be sucking air out of the case. When they are connected the other way around things get hotter (and suck dust IN) | Agent_24 (57) | ||
| 382020 | 2005-08-18 09:00:00 | it depends a lot on how the heatsink is designed . just to annoy graham it dos actually make a BIG difference which way around the fan sits . most heatsinks are designed for air to be blowen down on them . putting the fan on upside down results in one hot cpu . some (noteable alpha) have the fans that suck air away from the heatsink . simply put, leave it the way the manafacture made it . |
tweak'e (69) | ||
| 382021 | 2005-08-19 03:19:00 | But I'm not annoyed . So most manufacturers agree with my preference? Assuming the manufacturers know what they are doing will usually be a good idea . (Especially if they agree with me . ;)) Air expands by about 6-7% when it is heated from 20 degrees C to 40 degrees C . So that's an indication of the extra amount of air a "suck" fan should move . Fan/heat exchanger combinations should be designed with more margin than that, though I suppose they are made as cheaply as possible . |
Graham L (2) | ||
| 382022 | 2005-08-19 03:46:00 | I'm going to be pedantic again. My inclination is for the "blow" system. yeah - what we said.... |
pctek (84) | ||
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