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

[Skybuck Flying]

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.

HERE IS HOW TO RESOLVE/IMPROVE THE SITUATION:

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:

1. WRONG DESIGN:

HEATSINK FINS:

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

2. BETTER DESIGN:

| | | | | |
|
| | | | +------+ | | |
| | | | <---- 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.

Bye,
Skybuck.

 

[Skybuck Flying]

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:

1. BUILD A DUST/PARTICLE LAB.

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 !

Bye,
Skybuck.

 

[Skybuck Flying]

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
term.

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...

THIS REMAINS TO BE TESTED ! =D

Perhaps someday... a dust particle simulator might show what happens

Bye,
Skybuck

 

[MrTallyman]

I am starting to believe

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
it.

 

[Flasherly]

I have this theory that the fins of a heat sink should reduce a fan's
free-flow rate by 50% for optimum heat transfer.

Unless chambered to stop air flowing in for an arbitrary 10-25%
reduction of motor shaft speed, equal to chambering outflow, or both
chambered, as opposed to an effective vacuum, which might further
indicate where motor design is outside operational efficiency,
irrelevant of equipment MTBF, and provided there's salience to some
residual mean temperature for cooling to be a factor in coincident
significance to ascribe at the proposed structural end as an operative
upon RPM.

 

[Robert Macy]

I have this theory that the fins of a heat sink should reduce a fan's
free-flow rate by 50% for optimum heat transfer.

optimum heat transfer? not sure what the criteria would be, but think
instead about the air's thermal mass, thermal resistance form metal to
bulk air. and you see you're left with characteristics of the heat
sink, not the characteristics of the fan.

As a mind argument enfisionone hell of a powerful fan. Now block that
to half flow, what do you have? versus an 'underpowered' fan that is
blocked to half flow. .

 

[DK]

You are of course assuming that you know more about cooling a CPU than
all the people who currently make a living cooling CPUs, including the
MEs in charge of thermal design at Nvidia.

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'
competence.

DK

 

[Quadibloc]

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

The reason the heatsink _has_ fins is to maximize the contact area
between the heatsink and the air. So you also want to maximize the
velocity of the air in proximity to every part of the heatsink, so
that there is a larger temperature difference over as much of that
large contact area as possible.

One puts a dust filter in front of the intake vent to keep dust out of
the fins, although dust generally does not collect where there is a
violent wind.

What you really want to do, though, is use a working fluid other than
air which can carry more heat away. Of course, the Montreal Protocol
because of the ozone layer makes that more complicated; the other
alternative requires careful precautions because it becomes
electrically conductive very easily by dissolving material.

But a third alternative to setting up a refrigeration system and using
chilled water would be using chilled mineral oil. Of course, there,
flammability is a problem, although the fractions typically used for
such purposes aren't too bad...

John Savard

 

[SC Tom]

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'
competence.

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

 

[Mike Tomlinson]

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'
competence.

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.

 

[Flasherly]

Umm, you would not perchance be employed in a government position (spin
doctor) ??

If I had my druthers, I'd as rather gainfully, that is contractually
and under government auspices, to be on your tax dollar, sic, whereby
to impose mandatory interpolation of required observances, forthwith
said forthrightly, such that as an agreeable conscientious citizen,
I'm sure you are, there could be no other possible meaning given you
to mistake my greater schemes.

 

[DK]

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.

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.

DK

 

[Tim Williams]

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
physics.

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.

Tim

 

[upsidedown]

However, air expands when heated, causing an increase in air flow at
the exhaust end. That's why the exhaust port for a heat removal
system is larger than the intake. My guess(tm) is that the increased
exhaust air flow caused by heating is much larger than the reduction
in intake air flow caused by the fins getting in the way.

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.

 

[upsidedown]

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.

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.

 

[Martin Brown]

Minimum theta would do.


but think

If the heat sink doesn't reduce air flow at all, the air is going
around the fins, not through them (as Skybuck suggests) and the air
does no good. And if you block all the air flow, it does no good. So

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.

the amount of airflow restriction that results in the lowest theta
must be somewhere between those two extremes. Dead center is a pretty
good guess.

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.

Regards,
Martin Brown

 

[SC Tom]

If the input and output temperatures were the same, that might be
true. It might also be true if you consider the reduction in free
flow rate caused by the back pressure due to the head sink obstructing
the air flow.

However, air expands when heated, causing an increase in air flow at
the exhaust end. That's why the exhaust port for a heat removal
system is larger than the intake. My guess(tm) is that the increased
exhaust air flow caused by heating is much larger than the reduction
in intake air flow caused by the fins getting in the way.

On the original assertion, that it's better to suck than to blow,
methinks that's wrong. You can demonstrate this with a dirty
computer. Take a vacuum cleaner and try to remove the dust by
sucking. Most of it will still be in the machine when you're done.
Now, put the hose on the same vacuum cleaner exhaust and blow the dust
out of the machine. Notice that remaining dust is effectively blown
all over the room.

It's dispersion versus concentration. When sucking, one pulls air
from the sides and from all around the heat sink, including air that
does not need cooling. This makes the fan work harder moving excess
air, leaving less air flow for between the heatsink fins. Turn the
fan around and blow air at the heat sink, and the entire air flow is
involved in cooling the fins.

Similarly, you can demonstrate the effect by comparing the CPU
temperatures with the fan in the normal position (blowing air down
towards the heat sink), versus flipping the fan over and sucking air
out. I did this with a Pentium 4 dual core. I forgot the measured
temperatures, but the difference was substantial.

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.

 

[Flasherly]

Right.

I've bought about every heatsink or fan imaginable, given and within,
as another mentioned, an axiomatic engineering construct concept --
'if it's done right [in the first place], it's time to [attempt] an
improvement, [if and while not in need of entirely new construction
concepts]';- time simply follows, technologically speaking, to march
upon and then past any R&D Dept., in failure aptly to communicate, if
at least not uniquely, then an underlying implementation of adequacy
pertaining to key hard and software, constructional elements coming
in, daily, across so broad a field as computers. Where, specifically,
I see you for a fit is at a coincident juncture of heatsink fins and
augmented airflow, both being common terms to common acceptance for
pragmatic practice. The argument you have placed to ally yourself as
well follows true to the same axiom: that being one, effectively, of a
quest for perpetual motion: for so long as the key component of design
efficiency is established, widely employed to a common basis of
underlying industrial acceptance, the cost factor, then, is
effectively one which requires of me nothing more, out of my pocket,
than to advance a better sense of encouragement that such benefit, you
have chosen to propose, indeed, is of worthier consideration. Stop by
anytime if you'd like to talk, John. My office is at the top of the
stairs.

 

[Robert Macy]

Minimum theta would do.

 but think



If the heat sink doesn't reduce air flow at all, the air is going
around the fins, not through them (as Skybuck suggests) and the air
does no good. And if you block all the air flow, it does no good. So
the amount of airflow restriction that results in the lowest theta
must be somewhere between those two extremes. Dead center is a pretty
good guess.

--

John Larkin                  Highland Technology Incwww..highlandtechnology.com  jlarkin at highlandtechnology dot com

Precision electronic instrumentation
Picosecond-resolution Digital Delay and Pulse generators
Custom timing and laser controllers
Photonics and fiberoptic TTL data links
VME  analog, thermocouple, LVDT, synchro, tachometer
Multichannel arbitrary waveform generators

Doesn't lowest theta occur at MAXIMUM airflow? Think of it as a
stiction layer of air. All the heat from the metal must travel through
that stiction layer [which by definition is an insulative sheet of air
on the heat sink.] Now as air moves rapidly over the HS's surface;
that stiction layer becomes thin and voila! lowers the theta. That's
why all the HS curves of temp ris for given wattage always
asymptotically approach some value as the air speed increases. It's
because the stiction layer can be thinned, but not removed.

 

[krw]

Minimum theta would do.

 but think



If the heat sink doesn't reduce air flow at all, the air is going
around the fins, not through them (as Skybuck suggests) and the air
does no good. And if you block all the air flow, it does no good. So
the amount of airflow restriction that results in the lowest theta
must be somewhere between those two extremes. Dead center is a pretty
good guess.

--

John Larkin                  Highland Technology Incwww.highlandtechnology.com  jlarkin at highlandtechnology dot com

Precision electronic instrumentation
Picosecond-resolution Digital Delay and Pulse generators
Custom timing and laser controllers
Photonics and fiberoptic TTL data links
VME  analog, thermocouple, LVDT, synchro, tachometer
Multichannel arbitrary waveform generators

Doesn't lowest theta occur at MAXIMUM airflow? Think of it as a
stiction layer of air. All the heat from the metal must travel through
that stiction layer [which by definition is an insulative sheet of air
on the heat sink.] Now as air moves rapidly over the HS's surface;
that stiction layer becomes thin and voila! lowers the theta. That's
why all the HS curves of temp ris for given wattage always
asymptotically approach some value as the air speed increases. It's
because the stiction layer can be thinned, but not removed.

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).