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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. Guest

    The amount of heat power removed is directly proportional to mass
    flow, temperature rise and specific heat. With the exhaust temperature
    fixed due to the semiconductors, the heat removal can increased only
    by reducing the inlet temperature or increasing the mass flow.

    If the maximum exhaust temperature is +60 C, dropping the inlet
    temperature from +30 C to -30 C will triple the amount of heat that
    can be removed. For air, the specific heat is about 1 kJ/kg/K and air
    density of 1 kg/kg, 1 m³/s of air flow will remove 1 kW with 1 C
    temperature increase. With 1 l /s (1000 cm³/s) and 30 C temperature
    increase, 30 W can be removed. If the allowed temperature increase is
    90 C (from -30 C to +60 C), 90 W can be removed. With 5 m/s air speed,
    the duct cross section would have to be 2 cm².

    Of course, there are practical problems of transferring the heat to
    the mass flow.

    This is of course true, no argument about that.
    The problem is arranging the liquid cooling on a crowded PCB and the
    consequences of any leakage.

    Of course, if heat pipes are used and then the heat exchanger is
    cooled by tap water outside the box, will simplify things.
  2. Guest

    Or DimBulb. It's sometimes hard to tell them apart.
  3. Guest

    Sure, but the point is that far from what was stated, "Using refrigerated air
    for heat sink cooling is ridiculous.", it's commonly done. It's done both by
    separate air handlers and by integral heat exchangers.
    Refrigerating *air*, which is used to cool the heatsinks.
    If you need it, you're wasting too much energy. ;-)
    So you simply choose something else. Ether boils well enough to use in dunky
    birds. ;-)
    Water is a very poor choice, as noted. Fortunately, it isn't the only liquid
    available. There are all sorts of CFCs that can be tailored to pretty much
    whatever boiling point you wish.
    If you use the coffee cup, it has to remain full. ;-)
  4. Guest

    That is under normal atmospheric pressure (1 bar).

    Connect a vacuum pump and drop the pressure to 0.1 bar and the water
    boils at 50 C.
  5. You and Larkin are both idiots.
  6. Guest

    From you, AlwayWrong, that's some compliment.
  7. Jasen Betts

    Jasen Betts Guest

    I've observed this too, I first observed it playing with a squirrel-cage fan
    driven by a 1200W series universal motor (Electrolux :) ) The universal motor
    made it more obvious because these motors respond more to load changes.

    Modern cooling fans often have a pulse output that indicates fan speed, but
    monitoring software seems to only alarm on a low speed, where a high speed
    should possibly also be alerted as it may indicate a clogged heatsink.

    The fans with a PWM input would be harder to handle as the pwm to
    speed relationship would need to be compared
  8. David

    David Guest

    All of you are responding to a known troll and idiot, Skyduck Farting.
  9. Charlie E.

    Charlie E. Guest

    Actually, you find out that in this sort of system, the humidity
    increases the efficiency of the operation, since you now have a phase
    change step in operation. A design to use this type of cooling for
    automotive use actually added a supply of water to spray into the
    intake after they tested during a thunderstorm and saw the marked
    increase in performance!

  10. "Jeff Liebermann" wrote in message

    On the original assertion, that it's better to suck than to blow,
    methinks that's wrong.

    I will draw a more detailed drawing for you what I ment with "suck". There
    is also some "blow" involved.

    Side view of proposed heat sink design by skybuck:

    <out----------- airflow -------------in FAN or CASE FAN
    <------------- airflow ---------------
    |^|^|^|^|^|^|^|^|^|^|^|^| <- suckage effect going up
    |U|U|U|U|U|U|U|U|U|U|U|U| <- heatfins

    By blowing air over the heat fins as proposed this will hopefully create a
    suck effect, sucking any dust out from between the heatfins

    I do see some problems with this design... the tunnel will be small.... and
    a big fan will have trouble blowing air into it... maybe a small one will be
    enough... low rpm hopefully.

  11. "Timothy Daniels" wrote in message

    Given the same mass/sec flow of air over the fins of a heatsink,
    the best heat transfer is by blowing due to the greater turbulence -
    which disturbs the boundary layer of air that lies in contact with
    the fins and puts more flowing air in direct contact with the surface
    of the fins. In the case where the fins rise up away from the source
    of the heat, it's best to blow downward from the ends of the fins
    toward the source of the heat. IOW, the air should move in a
    direction opposite to the heat flow.

    This principle is not only used in heat transfer systems, but also in
    biological systems in oxygen transfer through membranes - as in
    fish gills where the blood moves across the gill membrane in a
    direction opposite to the flow of water. The basis of this principle
    lies in the finite heat (or gas) capacity of a fluid and that greatest
    heat (or gas) flow occurs as a linear function of the difference of
    temperature (or gas concentration) between 2 bodies. Apply a little
    calculus, and the principle of opposing flows results. This design
    principle was recently seen when I opened up the case of a friend's
    PC to clean it out: The cooling fins for the CPU rose up from the CPU,
    and the cooling fan blew air down along the fins toward the CPU.
    Obviously, the designer had paid attention during college freshman

    I'd love to see simulation that actually includes dust particles and hair to
    see how much effectiveness remains for this theory.

    I suspect the simulation software used at the time did not include these
    factors, and therefore all designs might be totally wrong for dusty/hairy

  12. wrote in message
    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.

    I like this idea of a closed air system very much...

    Maybe a case which is build entirely out of "heatsinks" or something... to
    get rid of as much heat from inside the case to the outside...
    without actually sucking in any dust/hair.

  13. Also perhaps a vaccuum would be created on the suck sections.

    So then on the bottom little holes would need to be made to create little
    openings to let air in...

    So then it starts to seems a little bit more like the blown through
    design... but this would be
    some kind of hybrid design.

    Some blow through and some suckage ;) :)

    Hopefully dust won't be sucked in from those tiny little holes... or at
    least a whole lot less then the other designs...
    otherwise it would be pointless.

  14. Well, if this is the case, if it's the case of maximizing contact area then
    here is an idea for a chip/gpu:

    The gpu is cut up into many tiny little pieces.

    The tiny little pieces are distributed over the entire graphics card.

    Tiny little heatsinks which are larger then the gpu piece are stuck on top
    of it.

    This should maximize the area a bit more... better distribution of heat.

    Since it's a parallel chip consisting out of multiple cores... it should be
    possible to cut up those cores and distribute them
    across the graphics card...

    Added benefit is also more lanes towards all tiny little cores... for more
    bandwidth and more memory lookup power.

    These tiny little gpu pieces could by stuck between capcitators... or maybe
    even on top of them... or vice versa...

    Not sure if that's a good idea... or where to best place them... but some
    spreading out seems nice.

    If this would be any better than current situation remains to be seen...
    current heatsinks also pretty massive
    across the graphics board... so maybe it don't matter, or just very

    Or maybe it does matter... maybe having everything on a small little area
    prevents optimal heat transfer...

    Thus cutting the chip up into multiple pieces might make it better.

    Maybe the entire chip design should be more like a building with windows in
    it... and blow air directly through the chip... instead of an additional

  15. "John Larkin" wrote in message

    It's been done, with better working fluids. You have one in your

    Yeah in case such a special case does not exist, a next best thing might
    simply be a mini/tiny refrigator and place the entire pc inside of it...

    My fridge actually has small little holes on the back side... so some cables
    could go through it...

    But it's a scary idea... electronics and moist.... hmm I'll have to look
    into this somemore...

    For now biggest drawback could be noise of fridge.... or maybe fridge can't
    handle the pc heat at all...


  16. Martin Brown

    Martin Brown Guest

    Convective and radiative cooling only. And not much of the latter if the
    thing is made of shiny metal. Proportional to flow plus a small additive
    constant isn't exactly rocket science. In any forced air cooling design
    worth its salt airflow cooling totally dominates.
    PWM to vary the power provided to the fan so the work done by the fan is
    on moving the air through it and to first order the output velocity
    field scales fairly well apart from deep inside the heatsink where there
    is or should be some turbulence.

    It occurs to me in this discussion that the performance of a standard
    rectangular vaned heatsink might be improved by putting diagonal wires
    through the vanes at say 45 degrees to generate vortex wakes that mix up
    the laminar flow after the first or second set of vanes.
    Measuring rpm of the fan against power supplied will give you a decent
    proxy for back pressure and many PC fans are so equipped.
    Perhaps but I would guess only by coincidence since the main output
    drive buffers are probably physically close to the edge of the die.

    Martin Brown
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