Is there much difference in having a fan blowing air into and thru the radiator to the outside, in comparison to one blowing air in thru and then having one suking air out? Hopefully this picture should help you see what i mean! One fan design fan (pushing air ->) ---> radiator -------> outside world Two fan design fan (pushing air ->) ---> radiator -----> fan (pulling air)----->outside world That should make it clearer!
A double fan arrangement should in theory create a stronger (not faster) flow, but in reality tests have found it to make no difference (on a Black Ice Xtreme at least).
I've always found it better to have the fan pulling air through the rad rather than pushing [edit] in a single fan config [/edit]
The dual fan design only really helps the one fan get its max rated cfm which is probably why it didnt show much of a temp difference from just the one fan setup...
I think this post explains fan directions best. Basically use your hand as the gauge. Does it feel cooler pushing air across it or pulling air across it? As for one fan one each side of a radiator... I would guess there is a small difference but if it was much the automotive industry would be using it I'm sure.
What I learnt from the same thing displayed by alpha heatsinks since way back when, is that if you have a fan directly mounted to a heatsink or radiator, it tends to need to blow in to perform best by passing as much air as it can over the fins, thus dissipating the heat quicker. If however, (as in the case of the alphas) you have a full or partial shroud sealing the fins in a partial duct with the fan (sealed) at the other end, you can sometimes get better performance sucking through this as all the air is drawn in through the maximum surface area (unconstricted by the fans' frames or centres) and gives better total coverage. It's never as simple as that though. Get the duct too long, you induce laminar (straight) airflow, as opposed to turbulent which helps carry the heat away from the vanes better. Too short, you get the same dead spots as before. This is why it helps to mock up a shroud out of cardboard/duct tape if you're building your own, you can experiment with what's best for your setup. But still, directly attached, no shroud = blow in Spaced (correctly) and shrouded = blow out. As always, there are exceptions - for a top mounted rad, on the topside sucking out is ok as the case itself sorta forms a duct, plus heat rises, so if you blow in, you'll want some pokey fans on the back to draw out what you're pushing in. [Edit] Netpapa - with cars, you get a 70mph gale blowing in the front under full load though...
Sucking air through a radiator may be noisier than blowing air through it, it depends on the bearing (re thrust reaction noise) and the airflow cfm (re turbulence noise). Generally obstructions on the intake of higher cfm fans are noisier than on the exhaust. Using a duct is useful, but most useful is getting the heated air straight out of the case rather than a) recirculating it or b) relying on the case fans themselves to extract that heated air. 300cfm will cool 1500W, 100cfm 500W, so not an excessive amount of air is required to cool a 85-150W of radiator load. -- Dorothy Bradbury http://homepage.ntlworld.com/dorothy.bradbury/panaflo.htm (Direct)
wouldnt having a duct, with the fan as an intake create a sort of "compressed" air type area, and create a stronger force?
you should find that sucking air thru any sort of inhibitor (ie: radiator) is better than pushing. this is becasue the the fan moves the air bu creating a presure drop on the underside of the fins as in rotates. air from the surroundings moves in to the vacuum. the top side then pushes this air along creating the flow. if there is a presure drop on the side of resistance then there will not be a huge drop in cfm because the air can still easily move away, as air can disperse quickly. however if the resistance is on the push side then the air cannot disperse so quickly and the vacuum created will be filled in part by the air on the top side. in short sucking is more powerful....
I guess you have to ensure that all the air moved by the fan is pulled through your radiator and air leakage is kept to a minimum for maximum effect, I can see it doesn't matter how much air your fan moves if diddely squat is actually coming through the rad it isn't going to help temps much.
