On 12/1/2018 6:12 AM, Paul wrote:
J. P. Gilliver (John) wrote:
In message , Paul
writes:
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Where the fan blows down onto the heatsink, the
dust will be near the top of the heatsink. A
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What proportion of such fans blow onto the heatsink, as opposed to
sucking off the heatsink - about 50-50, or is one type much commoner
than the other?

I know "clean box" cabinets tend to operate under positive pressure,
which is counter-intuitive (though does make sense when you think it
through), but there the concentration is on air filtration, rather
than cooling.

JPG

Most of these will blow the air downwards, which
can help cool the Vcore regulator or any other
VRM-like portions near the CPU.

Drawing air upwards has been tried, but doesn't
work quite as well. The design the OP has, has no
plenum to speak of, and a "suction" design would
need a plenum to maintain pressure.

*******

Dust in computer cases, is a function of positive
or negative pressure. And fan location makes a difference,
in terms of "stirring" the dust until the air vents
out the back. With some fan installations "dumping"
more of the dust load into the PC, than others.

Some PCs have dust filters on the front. All
that this does, is guarantee a cleaning job every
three months. And you have to position the
PC, so you can pull the washable filter out of
the computer case (at the bottom front). Without
the dust filter, the same PC can run for a year
or two, without a cleaning.

Â*Â* Paul

I have "positive ventilation" on my desktop. I have a 5" fan at the back
of 3 unused drive bays. The fan has a manual controller on it to
moderate the noise and air flow, and it draws air into the computer
through the drive bays. In the front of the fan, I have 4 1/4" layers of
soft foam packing material which air easily goes through. The foam is
hot glued together on alternate front or back edges to form a W shaped
filter element. Every couple months I remove the filter and vacuum it
off, then replace it. This is very effective at limiting the dust that
gets to the heatsink or elsewhere inside the computer, so I only need to
open it up for cleaning every couple years. I used packing tape to block
up "leaks" through holes in the drive bay sides.