haha call me a fool but just want to know.....
pulling and pushing air
Moderators: NeilBlanchard, Ralf Hutter, sthayashi, Lawrence Lee
pulling and pushing air
what is the theory behind pushing air towards a HS and pulling hot air out of a HS? which method is more effective?
haha call me a fool but just want to know.....
haha call me a fool but just want to know.....
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dukla2000
- *Lifetime Patron*
- Posts: 1465
- Joined: Sun Mar 09, 2003 12:27 pm
- Location: Reading.England.EU
IMHO ... (and also applies to the positive/negative case pressure debate)
There is no difference between pushing or pulling - moving air (aka wind) is the net result. And moving this air is the basis of cooling a heatsink.
However, there are all kinds of subtleties including:
- an obstruction close to a fan inlet typically cause more noise than the same obstruction the same distance from the fan exhaust
- The air input to a fan is pretty laminar, the exhaust is pretty turbulent. Turbulent air can be more effective at cooling a heatsink
- Similar to second point, the 'footprint' of the air input and exhaust is different. The exhaust tends to have most velocity at the tips of the fan blades (and a dead spot near the hub).
- In dirty/dusty environments, it will be desirable to place the filter in the fan input so the fan itself receives the benefit of the filter (but see point 1)
A clear example of the problems from point 3 is that a 30cfm 6cm fan on an SLK800 heatsink gives better cooling than a 30cfm 8cm fan. Unfortunately at the expense of more noise. Also, depending on the 'local' environment (cool air paths especially) near your heatsink, you can sometimes get a better result by putting your fan on the 'wrong' way.
So in balance 'good' hs design could be either way, and the 'best' results are very dependant on each setup.
There is no difference between pushing or pulling - moving air (aka wind) is the net result. And moving this air is the basis of cooling a heatsink.
However, there are all kinds of subtleties including:
- an obstruction close to a fan inlet typically cause more noise than the same obstruction the same distance from the fan exhaust
- The air input to a fan is pretty laminar, the exhaust is pretty turbulent. Turbulent air can be more effective at cooling a heatsink
- Similar to second point, the 'footprint' of the air input and exhaust is different. The exhaust tends to have most velocity at the tips of the fan blades (and a dead spot near the hub).
- In dirty/dusty environments, it will be desirable to place the filter in the fan input so the fan itself receives the benefit of the filter (but see point 1)
A clear example of the problems from point 3 is that a 30cfm 6cm fan on an SLK800 heatsink gives better cooling than a 30cfm 8cm fan. Unfortunately at the expense of more noise. Also, depending on the 'local' environment (cool air paths especially) near your heatsink, you can sometimes get a better result by putting your fan on the 'wrong' way.
So in balance 'good' hs design could be either way, and the 'best' results are very dependant on each setup.
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Ralf Hutter
- SPCR Reviewer
- Posts: 8636
- Joined: Sat Nov 23, 2002 6:33 am
- Location: Sunny SoCal
The theory behind the Alpha heatsinks (that are designed to suck air off the heatsink) is that the shroud that fits over them forces the air to be pulled in around the base of the heatsink (where the temperature is the hottest) first, then it flows up away from the hottest point of the HS up through the fan. This system utilizes the coolest air at the hottest point of the heatsink so it cools better than a typical heatsink that uses air that has already been heated as it travels through the heatsink from the top to the bottom.