Does Push/Pull System in CPU heatsink work?

I believe the pressure of the two would make the temps better. It does help the temps because ive tested it, i just dont know why.

air simply does not want to go through the fins so easily - the second fan pulls air from between the fins etc helping the fan push air into the fins etc and extracts the air flowing through the fins

simple test - blow air at your fingers while leaving small gaps in between - the air flow behind your fingers is perhaps 1/10th the original air speed etc

Using an axial flow fan it is optimal to use a fan with eight or more blades with bevelled edges and curved tips. This is the most efficient style PC cooling fan. It's a lower speed fan (1800 rpm or less) that produces less noise while moving the same volume of air compared to higher speed fan (2400rpm or higher).
As well a fan with a sleeve bearing is preferred because it accommodates the thrust effect when the fan is under load. (The fan is under load when it pulls air across the heat exchange surface.)
If this is for your cpu heatsink this style of fan is found on the more expensive ($50 or more) cpu coolers.

On a side note: Sleeve bearings have a lower MTBF (Mean Time Between Failure) rate compared to roller/ball bearings. In other words, ball bearing have a longer working life compared to sleeve bearings. However there are hybrid sleeve bearings called fluid bearings or fluid magnetic bearings that have longer working life than roller/ball bearings. Fans with this style sleeve bearing are found on more expensive cpu coolers.

I tried it once (Q9550, TRUE, two S-Flex SFF21F fans, Antec 900 case, HSF oriented vertically). No significant improvement in my case. May have been because the top fan was pretty close to the big case fan.

Of course, YMMV.

Makes sense. Rotating the heat sink 90 degrees in a normal case is not an answer either. So maybe its only effective with a weak fan on the exhaust fan side of the heat sink. Or with the cooler rotated 90 degrees in a case with a top exhaust and some headroom.

This review of one such multi-fan-capable cooler shows that the gain may depend on fan speed . . . and if one fan is fast enough, the second may not matter (ex/noise).

http://www.legitreviews.com/article/1053/1/

I'm sure you can find other examples and comparisons by googling "Scythe Mugen 2 review", and any other cooler that's 2-fan capable.

Yes, the use of mutiple cpu heatsink fans will not produce spectacular results. A difference of about 2C or 3C is all that one should expect. For the typical user it probably won't make any difference. For a hardcore gamer it might.