One problem with computer fans is they get stuck in dust.
Whether
it be a little fan on a graphic card or the computer's huge
power supply block fan, after a year or so they are smeared in
fine dust
filaments. If a heatsink is placed beneath a fan it can
accumulate quite a bunch of dust. This lowers the cooling performance
of the fan and even can make it become noisy. Some people do
open their computer once a year and vacuum clean all that dust inside
and around the fans. Other ways round can be these:
Self-cleaning
fans
The obvious way to make a self-cleaning fan is to make it able
to turn in both directions. By blowing the opposite way the fan
will blow away at least most of the dust that accumulated. There are
variants to this basic principle:
The fan can blow half the time in one direction and half
the time in the other direction. I'm not sure this is the best solution
because in some cases the dust will not be blown away. For example
there where the air speed is quite low. I fear it may tend to make even
more dust accumulate. Because the dust filaments stretched towards one
direction will make other dust filaments blown the other direction
adhere easily. Like a comb retains hair.
The fan can once in a while blow much stronger. This will
blow a part of the dust away.
A friend told me on industrial systems he installs very strong
fans in order to permanently prevent the dust to adhere. This
may cause problems because there will always be places the air slows
down and dust does deposit. Besides a very strong air stream can cause
problems on itself. A solution can be quite a little system, composed
of a little yet powerful compressor that blows air at a very high speed
through a little and enclosed heatsink. The air output would blow
towards open space where the air would slow down without particular
possibility to deposit dust. This has the advantages to be little and
avoid most dust deposit. On the other hand it is more power consuming
and more difficult to keep noiseless.
An interesting possibility is a mixture of the above: a fan that
once in a while starts blowing the opposite direction
and with more force. This will detach and expell most of the dust.
Blowing the other direction requires the fan blades to be flat
and not curved. In order
to be able to blow efficiently in both directions. This in turn
requires the fan blades to be not too much inclined. Which
requires the fan to run faster to get a same air flow. Or to
have two propeller stages and maybe two static stages like a
compressor. The fact the fan has to be able to blow a least a
short time at high speed requests for a stronger motor and a little
more sophisticated electronics. This ensures for a more reliable
functioning at standard speed which is a good thing.
Next puzzling is what should trigger the fan to blow the
opposite way. Many criteria can be proposed:
The fan can do that on a regular basis. Say every month or
every one million turns. The problem is the noise generated during that
process and possibly the dust cloud can be surprising and annoying.
The fans electronics' can compare the turning speed to the
voltage and infer when the fan seems to be stuck in dust. This
is a quite unreliable criteria to me because many things can make the
fan turn slower. Anyway this could be used if linked
with other factors and a rudimentary neurons network.
The fan can be triggered to blow the dust away by the
computer's user. Tuning addicts would be glad to have buttons in a
window or on or their computer's case for this purpose. The way the
fans are linked to the command buttons are a matter of
questioning too. That can be a dedicated USB device, an on-board
motherboard function, wires and buttons, a sound-tone code listening
microphone inside each fan...
What will happen with the dust blown away? Part of it will
fall to the bottom of the computer which is not a problem. Another part
will be propagated to the room the computer is situated which is more
problematic. It may also trigger health
accidents like asthma. Opening the windows can help. A partial solution
could be to synchronize the fan cleanings. First the computer's main
fan situated in
the power supply block should
do a short and powerful cleaning. This will generate a dust cloud
inside the computer case. The fan should immediately
stop. Then the other fans, situated on the motherboard and cards
should clean, adding their dust to
the the dust cloud inside the case. Then the computer should go into
low power consumption or shut down, till most of the dust did deposit
on the bottom of the computer case.
Aspirate
the air from the heatsink instead of blowing towards the heatsink
If the ventilator blows towards the heatsink the dust will accumulate
between the ventilator and the heatsink. This makes the dust quite hard
to clean. A solution is to turn the ventilator 180° and make it
aspirate the air from the heatsink. That way the dust will accumulate
on the open sides of the heatsink and it will be much easier to clean.
I wrote a Web
page about this.
Filtering
the air
The air that goes into the computer can be filtered. This can be done
by making wide openings in the computer case (covered with conductive
grids to disallow RF noise). Then tape pieces of tissue on all
openings. Probably they should be replaced or washed once in a while.
The more you're using your computer the cleaner the air you breath.
Another way round is to turn the computer mains fan so it blows
the air towards the inside of the computer. Then place sort of a car
air filter at the entrance of that fan. This can be done a neat
way. The advantage is the rest of the computer case can remain the way
it is.
A friend used to let an electrostatic air
purifier on in his dark chamber. This allowed him to get a clean room
and produce neat photographs. All devices inside the dark chamber
remained dustless. Such a purifier is not very expensive. Yet be
careful
not to take risks for your health. Bad purifiers can produce dangerous
ozone gas.
Another friend is going to tape tissue filters around the air inputs of
his processor heatsink. These filters need to have a lot more surface
than the surface of the heatsink inputs.
Liquid
cooling
A high-tech way to cool a computer's hot parts is liquid cooling. The
advantage is you don't get the parts dust in by an air flow. Even if
they should get dust in this won't hamper. The liquid circuit's
heatsink
itself can get dust of course. But it can be placed a way that makes it
easy to clean it.
Static
cooling
A huge heatsink does not need a fan. They imply slow air speeds
which cause few dust deposit. A compromise is to use such a huge piece
to thermally link the warm part with the case. The problem with this
solution is it implies huge, expensive and heavy heatsink parts.
Another compromise is to use a regular heatsink, just a little bigger,
and a slow air flow by a big ventilator turning at low speed.
Mechanically
cleaning heatsinks
Insects clean themselves continuously using their legs. Maybe a fan and
heatsink system can do the same. Sort of a comb system
interlaced with the heatsink can be kept slowely moving and scrape most
of the dust away.
Closing the
computer case
The computer case can be completely closed. That way no or few dust can
penetrate and spoil the fan and heatsink blades. This can be
done by shifting the power supply block a few centimeters to the inside
of
the computer and tape close most openings and grids. The point is a
reasonably strong fan should be present inside the case, to make
the air move and mix fast inside the computer. The outer surface of a
computer case is quite huge. To me this is enough to evacuate the
heath provided the inside fan ensures the hot air is
continuously smeared all over the inner surface. Maybe the power supply
block fan is enough to achieve this, perhaps helped by cardboard
shapes. 'Think I'll try that on my computer.
Should the case surface not be sufficient then that surface can be
rippled like heatsinks are. An outside huge and very slow turning fan
can
be also be directed towards a part of the surface.
This approach has also to advantage to lower the computer noise. But
this means the inner sides of the computer case should not be too much
covered with thermally insulating sound-deafening materials.
I didn't try out with my own computer because it's not in a case. Its
components are spread all over my table. I used an old Pentium II
computer a friend gave me. It has a horizontal case which makes the
experiment a little easier too. I unscrewed and pushed the power
supply block about 5 centimers towards the inside of the case (see the
drawing
below). I put a cardboard
wall (red) above it in order to force the air to circulate inside the
case and not be swallowed immediately back again by the power supply
block's fan. I closed all holes of the case with removable tape
(especially the 9 centimeters diameter wide hole left by the power
supply block fan) (orange).
There just remain a few half a millimeter wide slits around the case's
surface (actually there is
no need to make the case hermetically closed and this could even be
dangerous because of water condensation). The result is perfect. I
launched a very long and power-consuming calculation. After half an
hour time most of the case surface simply is cold. The power
consumption of
that old PC is about half that of today PC's. Anyway a little less cold
than perfectly cold would still be very cold. The only tepid part I
could feel is a little surface part at the rear of the case. That's
because the mains' fan, which is now enclosed inside the case,
is blowing towards towards that part of the case. The temperature is
that of the hot air that fan always has blown. Two decimeters to
the left of this tepid part, above the motherboard, the case
temperature is cold. It really is a success. With no design effort.
The computer also makes less noise. No opening or expansion possibility
has been compromised. I don't understand why this design is not widely
used. Since a human generation time personal computers have gone dirty
in dust and go malfunctioning. Just shifting the main power block 5
centimeters aside solves the problem. This also generates a little
stronger air circulation inside the computer, which makes the
components a little cooler. There is less fire hazard since
a fire cannot start inside the computer, be fed by air and spread to
the outside. There is also less danger children put an electric wire
inside the power supply block.
A friend told me I should put a temperature probe inside the case. I
did so, just in the middle of the air inlets of the power supply block.
After a long period of heavy calculations the temperature had risen to
39 °C. This is more than I tought yet still acceptable. A dedicated
air circulation design would be a good thing.
I removed the cardboard wall above the powersupply block and put a fan
to force the air to circulate inside the case. The result
was obviously better. The temperature at the power supply block inlets
rose only to 33 °C. There was no tepid zone feelable on the
computer case. Simply the whole case is no more "ice cold" like metal
normally is when you put your hand on it. Below are a top view and side
view drawings. I let the computer on for two hours without
calculations, the temperature didn't exceed 10 °C above room
temperature. Options to lower the case temperature down to
near room temperature are to paint the case black, put it vertically or
direct external silent slow turning fans towards the case. This
bears a market for design.
I thought to build a cardboard labyrinth to force the air coming out of
the power supply to first pass along the case's right side surface.
That way it would loose most of its heath before going to the rest of
the inside of the case. But I allready have good performances so I
probably won't try it out.
Placing a fan loosily above the computer surface didn't help. The case
surface feels colder yet the inside temperature probe shows no
significant temperature decrease. This is because the air inside the
case does not move fast on the inner surface of the case. The global
air motion inside the case may be fast but a millimeter above the inner
case surface it stands still. I solved that by placing two fans on each
side of the case, forcing the air to move fast on the case surface at
that given place (picture below). This allowed for a much better heat
transfer and
temperature decrease. The inside temperature is now only 6°C above
room temperature (no calculations).
This design became somehow ridiculous. It uses four fans and one of
these fans is on the outside so it accumulates dust. Obviously there
should be only one fan inside the case, that is the power supply fan.
It should be bigger and placed a way it makes the air circulate fast
inside the computer case. The heat transfer towards the outside should
be achieved by using a heatsink shape on both the inside and outside of
the
case. For example aluminum cylinders or blades placed wherever there is
empty space or there where the fan air flow is strong. There should be
no fan on the outside, just aluminum cylinders or blades pointing out.
I'll try to get hold of such pieces of heat conducting metal; aluminum
or copper.
The problem with a big aluminum heatsink structure is it will be heavy,
cumbersome and expensive. Since we asume an internal forced air
flow, a more lightweight and thiner structure can be used: just a
rippled surface. My best bet would be a vertical case with a rippled
structure on the right side (drawing below). There would be a thermal
insulation on the inside (orange). The inside side of the rippled plate
forms air ducts, leading the air towards the bottom. The air is forced
through these ducts by the fan (black) of the power supply block (blue)
at the top of the case. Maybe a flat plate can be place on the whole to
form a chimney structure. Provided that plate can be removed easily to
wipe away the dust.
I whish to thank Dimitry Gathy, Pierre Backers, Didier Bizzarri,
Frédéric Cloth, Philippe Thoma and the designers of early
Russian space probes for their ideas, additions to
this text, technical remarks and gifts of hardware.
