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Digressing slightly to a previous question about preferred fan airflow direction in one of the cooling posts, the answer is derived quite apart from any cooling consideration - wind velocity.
Depending on the fan type, typically the elevating type, designed to be vibration free, incident wind effect on the blades produces a very annoying harmonic which may not be audible, revealed only by touch.
The effect is eliminated by drawing air through the heatsink rather than blowing air into the heatsink. I think the latter is marginally more effective, but as I found, a significant problem in the field with any sort of breeze.
A crude analogy might be compressor blade stalling/surging in a gas turbine engine. This is controlled by the incidence of the airflow presented to the compressor by guide vanes - the airflow through the heatsink onto the fan guided by the fins is probably similar in effect.
Last edited by rcheshire; 12-11-2015 at 05:42 AM.
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