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(NVIDIA) Fan-Based-Heatsink Designs are probably wrong. (suck, don't blow ! heatfins direction)

Discussion in 'Electronic Design' started by Skybuck Flying, Aug 18, 2012.

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  1. Hello,

    I am starting to believe that NVIDIA's Fan-Based-Heatsink Designs like the
    recent GTX 690 are totally wrong !

    And here is why:

    The heatsink fins are placed in the same direction as the airflow. This will
    cause dust to easily get stuck between the heatsink fins and especially in
    front of it.

    THIS IS WRONG. This will cause the heatsink to get full of tiny little hair
    pieces and dust particles.


    Place the heatsink fins 90 degrees turned so that the overflow must go OVER
    the heatsink fins and not in between.

    So here is a picture to show the wrong situation and the better situation:

    top view of card when place on table:



    --------------------- <----- airflow | FAN
    <--airflow--- -----------------------


    | | | | | |
    | | | | +------+ | | |
    | | | | <---- airflow | fan | <--- airflow | | |
    | | | | +------+ | | |
    | | | | | | |

    This better design should hopefully and be designed in such a way... that
    air/heat GETS sucked out of the heatfins by blowing air OVER IT and not in
    between... to reduce the chance of stuff getting stuck in it !

    So there should be some room OVER the heatfins to be able to blow air
    through it.

  2. Additional:

    Since my horror experience with the 7900 gtx cards I am afraid to buy
    graphics cards with the nvidia heatfins direction.

    I am afraid that the graphics cards heatsink fins will get full of dust and
    stop to function !

    My newest passively cooled graphics card is actually also an nvidia/asus
    design. Where the heatfins are in the direction against the airflow.

    So far there is probably no dust in side of it... or very little... which
    seems to be much better.

    If nvidia wants my bussiness back they will have to design cards which can
    operate for the long term, without requiring any cleaning what so ever.

    I am not going to open up my PC and risk damage during cleaning operations.

    NO CLEANING operations should be necessary.

    THEREFORE nvidia must design graphics cards which will operate for a long
    time... 5 to 10 years of blowing/sucking air.

    Perhaps the heatfin direction that I proposed is less optimal in the short
    term... but will probably be optimal in the long term.

    Therefore my advise to nvidia which they hopefully already have:


    2. TEST the graphics card heatsink design for as long as possible... and
    test the situation with dust build up.

    3. Build the graphics cards which has the least problems with dust build up.

    Otherwise you can go to hell... I do not ever want to face overheating
    problems because of gpu overheat/heatsink full problems ! ;) :)

  3. One last explanantion/addition for any potential dumbos out there to explain
    the "suck, don't blow" part of the title.

    The idea is to:

    BLOW air OVER heat fins.

    Hopefully this will create some kind of suckage effect over the heatfins and
    suck heat from between the heat fins and blow it away.

    This might also have a beneficial effect of sucking any dust/hair particles
    out of it and blowing it out.

    That's the idea at least... which would be very nice.

    I am not sure if it will work like that in practice... since there is no
    opening on the other side of the heat fin to suck from....

    So maybe some kind of vacuum would result from it...

    If that is a good or bad thing remains to be seen/tested.

    Very maybe openings could create on the other side... but that would
    probably start to suck dust between the fins which would be bad.

    So experimenting with this idea is required to see what works best long

    My only worry would be that the opposite might happen, maybe dust will start
    to fall down between the heatfins....

    What will happen in reality I don't know...


    Perhaps someday... a dust particle simulator might show what happens ;) :)

    Skybuck :)
  4. MrTallyman

    MrTallyman Guest

    You are an idiot.

    They suck so that YOU still have direct access to clean the tines of
    the heat sink. If they blew, the heat sink would get plugged up in a
    place under the fan, and you would have to remove the fan to clean it.

    Now shut up and go away and stop making posts which you are then the
    only idiot who responds to it the first 5 times!

    Grow up, child! You are immature AND stupid. Get over it. Leave US
    out of it.

    You are a very particular type of Usenet idiot, and you are blind to
  5. DK

    DK Guest

    When a video driver installation takes 200 MB on a hard drive
    and is still full of bugs, there is every reason to question designers'

  6. SC Tom

    SC Tom Guest

    That's a different group of engineers. I doubt seriously if the design
    engineers are also the software engineers, although there is probably *some*
    collaboration between the two groups.
    The design engineers I worked with had a motto: "If it ain't broke, redesign
    it!" No such thing as leaving well enough alone :)
  7. Come on. That's software vs. hardware. The engineers may design and
    build superb hardware, but if the software isn't up to scratch, it's
    wasted effort. Look at ATi/AMD cards, for instance. Good hardware,
    lousy drivers.
  8. DK

    DK Guest

    I realize that. Just couldn't resist. Plus, I think it points to some
    fundamental management/business philosophy problems that are
    very likely to influence all layers in the company, harware included.

  9. Tim Williams

    Tim Williams Guest

    Oddly, my new, stock heatsink is designed with fins arranged
    not-quite-radial, in an X pattern around the center. It looks like
    extrusion oriented axially (axis normal to the processor face), rather
    than transverse. The fan blows air over the center and fins.

    At 100% CPU I get 42C tops, so it seems to be doing its job. Nothing
    special, a dual core 3.2GHz Athalon II. It's also entirely possible AMD
    (or whoever they contracted to make them) doesn't know their physics.

    Note that heat transfer by volume isn't usually the goal, so much as
    minimum temperature is. In a counterflow setup, the hottest part of the
    heatsink is cooled by the hottest air. If you flip it around, the hottest
    part of the heatsink gets cooled by the coolest air, achieving the highest
    heat flux for a given surface area and temperature difference -- more
    power density, at some expense to mass flow and pumping loss. You might
    avoid this, for example, if you had to use pure nitrogen (or helium, for
    that matter) for some process, minimizing the gas flow to keep operating
    cost down.

  10. Guest

    The air density drops from 1.2 kg/m³ at +25 C to about 0.6 kg/m³ at
    +325 C, so yes, it might make sense to double the exhaust cross
    section area.

    However, for practical semiconductor cooling applications, with intake
    temperature at +25 C and exhaust temperatures below +60 C, air density
    is about 1.07 kg/m³, an expansion is only about 10 %. I doubt it
    would make much sense to try to optimize exhaust areas.
  11. Guest

    Why not use compressed/expanded air for this purpose ? Using a piston
    compressor to compress the air to a few bars, the air gets quite hot,
    then let it go through a heat exchanger to get rid of most of the heat
    and cool the pressurized air closer to ambient temperature.

    Let the air expand to normal ambient pressure and the air temperature
    is now well below ambient temperature and let it flow through
    semiconductor heatsinks to the environment.

    To avoid problems with dust and condensation, a closed loop might make
    sense, but of course, now the heat exchanger would also have to
    dissipate the heat from the semiconductor. However, the heat exchanger
    can be remotely located and it can have much higher temperatures than
    the semiconductors, getting rid of the heat into the environment would
    be easier.
  12. Martin Brown

    Martin Brown Guest

    More to the point if the heatsink fins are not thick enough to conduct
    heat away from the thing being cooled it doesn't matter how easily you
    can push air through them. Equally it is no good if you get perfect
    laminar airflow since then only the air touching the surface warms up
    and the core air remains cool. So you have to have some turbulence and
    opposition to free flow but the tricky question is how much is enough?

    Something like this might be close :

    ====o ====o ====o
    ====o ====o
    ====o ====o ====o

    (slightly tighter together than ASCII art will allow)
    Airflow from left to right with a blob on the end to mix the air up.
    But also very probably wrong. The volume of air going through the heat
    sink is proportional to the amount of cooling you get for a given design
    so there is a definite bias towards not blocking off half the free air
    flow. I would guess at something more like allowing 2/3 to 3/4 of free
    airflow as about the best depending on the exact heatsink geometry. It
    could easily be higher - easy enough to do the experiment.

    I suspect the perfect shape for an optimum heatsink is rather more
    complex than the typical fins we get but the designs used at present are
    good enough and much easier to engineer. Heat pipes have helped
    enormously with the latest generation of quiet heatsinks.

    It is a sobering thought that high performance CPUs often have a heat
    output per unit area that exceeds the tip of a soldering iron.

    Martin Brown
  13. Gib Bogle

    Gib Bogle Guest

    You just invented the refrigerator.
  14. Gib Bogle

    Gib Bogle Guest

    Who would want to carry out repairs or mods on such a machine?
  15. Guest

    I know, I know.

    The point is that by using compressed air, problems with hazardous
    substances and circulating liquids can be avoided.

    The problem is how to solve the problem with humidity in the air,
    which might condensate or even form ice, when sub-zero air
    temperatures are used. The situation gets complex during startup,
    reboot, shutdown and especially during a power failure. If the
    humidity can be removed somewhere before expansion, the situation is
    greatly simplified.
  16. SC Tom

    SC Tom Guest

    I tried that on an old AMD and got the same results; the CPU was much hotter
    with the air being pulled through than it was with it being blown through.
    One of the electrical engineers at work explained it this way: If the air is
    being pulled through, most of the air is moving through the fin area closest
    to the fan, with the lower fins (closest to the CPU) getting the least
    amount of flow. Therefore the heat has to transfer through the fins before
    it gets to an area where there is enough air flow to actually aid in heat
    removal. But, with the air being blown down, through the fins, there is
    enough back-pressure to allow the air to travel almost equally across all
    fin surfaces before exiting, carrying a larger amount of heat with it. Don't
    know if that's exactly how it works, but it made sense to me, and would
    explain why most newer heatsinks have the air blown through rather than
    pulled through the fins.
  17. Guest

    Volume is good, sure, but everything else equal,that takes a bigger fan. The
    question is, given a fan optimize the resistance. It's an impedance matching
    sort of question. Constrict the air too much, with heatsink blades and the
    airflow goes down. Open it up and there is no contact between the heatsink
    and air. As others have mentioned, the point isn't to reduce the boundary
    layer by increasing velocity, rather to upset the boundary layer with a
    turbulent flow. ...just enough turbulence to upset the boundary layer but not
    so much as to restrict flow. Just enough heatsink material to transfer heat
    and not so much as to restrict flow. It's not just a single variable
    equation. The heat-transfer people at IBM (sat down the hall from me, moons
    ago) used our electronics simulation programs to design these things. Their
    sim models were just as large as ours and took just as much CPU time (hours).
  18. Guest

    Air has a very low specific heat. Liquids are much better. Phase change is
    even better but you still have to dump the heat somewhere.
    How about out the drain connection? ;-)
  19. Guest

    IBM mainframes all used chilled air for the peripheral components, like
    memory, power supplies, and controls; anything that was card-on-board
    technology. Smaller systems used chilled air from under the floor (heat
    exchanger not built into the system).

  20. Tim Williams

    Tim Williams Guest

    Indeed, and add to that the fact that fans are not "resistive" air
    sources. The peak power point (pressure * flow) occurs at a pressure of
    about 25% of maximum (fully blocked) pressure. You can't operate very far
    from this condition or your flow will be too slow.

    If you include dynamic pressure (mass flow), fans are even more nonlinear.
    Next time you have a squirrel cage type laying around, hook it up and play
    with it. Put your hand over the outlet. You'll find the velocity is
    great until about 1-2 diameters away, where you start feeling the force of
    ram air. Within about 0.5 to 0.25 diameters, pressure is maximum, because
    flow hasn't gone to zero yet, meanwhile static pressure is building. Put
    your hand all the way up to block it, and static pressure goes to maximum,
    but velocity goes to zero, so the power you're feeling drops sharply.

    BTW, I use the example of a squirrel cage because they provide more
    pressure, making a more illustrative example. Regular axial fans do as
    well, and manufacturers typically provide comparable graphs.

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