Hold me CLOSE I'm a FAN???

[spykid]

Dose a heat sink fan have to be on the heat sink? A fan out in the open/attatched at the top, versus a fan in say a pvc tube a few inches away, maybe even outside the case...wouldn't the tube create more concentrated air flow if the tube/duct fits over/top of heat sink. Then maybe you could attach a much stronger fan inside the tube with less noise???

[TT120]

As long as the air is flowing over the fins on the heat sink, you should be alright. More air over the fins=more cooling power.

[Hoot]

An issue to be wary of is back pressure. Even in a smooth walled PVC pipe the is an increase in the resistance to air flow. Why does this matter? Axial fans do not perform well in the presence or airflow resistance. The manufacturers spec these things hanging in the air. Nothing impeding the intake or exhaust. Even small amounts of resistance to airflow cause the fans to leak air out the back because the pitch and width of the blades along with the depth of the frame do not allow the blades to exert a lot of force. Cage aka Centrifugal blowers overcome this by developing propulsion of the air in a different manner. They tolerate back pressure very well. Try it yourself. Power up a fan in the open and put your hand behind it. there is very little air coming out the back. Now move it close to a flat surface, say an inch or thereabouts away. Some of the air will hit the flat surface and deflect outward and some will blow out the back. Thicker axial fans and those with turbine style blades tolerate back pressure better.

Hoot