SLK-900u. Blow in or Out, anyone compared?

[shorton]

I am anxiously awaiting my soon to arrive Thermalright 900u heatsink (HS) for my P4 3.0/800.

It appears the recommended fanflow direction is into the HS. This seems illogical, and not best but I figured there must have been a reason.

It appears to me that "sucking" the cooler air in from the sides with the fan as an exhaust would be better. In that arrangement:
1. The cooler air may be drawn in where the HS is hottest, near the CPU
2. The exhaust air is exhausted almost right into my rear case fan (to be sucked out of the case) with less colateral heating of other components.

In the alternate, blow-in configuration:
1. the cooler air enters the HS at it's coolest point and is heated as it proceeds toward the HS and CPU core.
2. The hot side exhaust will a) wash over the surface of the MB, further heating other components, and b) blowing right up to my PS, thus providing it with a wash of warm air. c) the turbulent exhaust will be more prone to immediate re-entry into the surce air of the fan, thus not giving the best intake air (of course this could be solved with some easy ducting)

It seems that an ideal arrangement might be a fan, sucking out (exhausting) from the HS. This arrangement may be improved further using a 92mm fan (or even a 80L) and ductimg to insure all of the airflow produced by the fan is directed through the HS, while at the same time helping to reduce any "dead spot" created by the realestate occupied by the fan motor.

Why is "into the fan" the recommended configuration?

Comments, experiences? Anyone done any ducting with this HS?

Cheers,
Scott

[SpyderCat]

It appears to me that "sucking" the cooler air in from the sides with the fan as an exhaust would be better. In that arrangement:
1. The cooler air may be drawn in where the HS is hottest, near the CPU
2. The exhaust air is exhausted almost right into my rear case fan (to be sucked out of the case) with less colateral heating of other components.

Comments, experiences?....

You're almost there Scott.
If you prevent the hot air from being recycled in the case, like shown here, the result will be that your case stays cooler. Any small loss in efficiency from sucking air through the heatsink will be more than compensated for as you suck much cooler air through the heatsink.

Regards, Han.