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

"Martin Brown" wrote in message
...
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.

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.

Tim

--
Deep Friar: a very philosophical monk.
Website: http://webpages.charter.net/dawill/tmoranwms

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.

Nope, no theta modules presently marketed, just a couple squirrel
cages and extant circular Zalman takes from a fairy good run given a
premium to pricing structures. Mass seems the byword, now-a-days,
massive as a restriction only limited by standardization among case
manufacturers. Had one recently, the typical behemoth of 7- to 1155
sockets, I picked for a proverberial song & dance, which barely missed
a nonstandard case construction I do own, within designer case
specifications by a mere 1/4", (yes, I simply had to measure it), as
opposed to a standard, however exact fit, such as Rosewill's
understudy of Antec cases. Excepting the fan -- I'd as well be
veritably ecstatic over results obtained within a reality of present
heatwick technology -- as it is, the size of an exterior case fan
ported and packaged to that CPU HS is at best, safer to defer for a
project to rewire its connection off the MB current draw and onto a PS
lead, proper.

As mentioned aside by similar instances of a P4 or AMD X2, a benefit
not only set to 107F (and lower, I reside at as low as 100F respective
to ambient temperatures), is a backtest of their efficiency to
approach flash computational processes conceivably closer to these
"soldering tips" of 130F, for as much in as least time possible then
to regain steady state 107F operational status. It's my own personal
theory, fwtw, that case designs importantly conducive to achieving
such good results, are at much an impasse the last generation of P4s
encountered before heading into nonlinear modes of augmented,
multicore processing. Extensively drilled, variously meshed and
screened, the approach has effectively advanced to a breadboard
construct from a standpoint of free air.

On Sun, 19 Aug 2012 09:25:59 -0700, John Larkin
wrote:

On Sun, 19 Aug 2012 08:47:26 -0700 (PDT), Flasherly
wrote:

On Aug 19, 12:12 am, John Larkin
wrote:

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.

Are you really John Fields?

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

[................]

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

The goal is maximum heat transfer per gram of air for the flow provided
by the fan, or calories/gm/sec. IOW, you want the most heat transferred
for the mass of air that the fan can move through the fins. (Note that the
volume of the air changes as it heats up, so mass is used in the calculations
instead of volume.)

And yes, in a counterflow situation (i.e. heat flowing through the fins in
a direction opposite to the flow of air), the coolest air contacts the coolest
portion of the fins, and the hotest air contacts the hotest part of the fins.
Since the highest heat transfer occurs where the temperature difference is
greatest, one might think that the greatest heat transfer would occur for
parallel flow situation. But no, it's the opposite when one does the calculus.
The reason is that the heat transfer in the counterflow situation works over
a longer period of time since the temperatures of the 2 media (i.e. fins and
air) remain different throughout the time of transit. In the parallel flow
situation, the greatest transfer occurs at the beginning when the 2 media
have the greatest temperature difference, but the temperature difference
falls of rapidly as the air flows toward the cooler part of the fins and the
heat transfer falls off as well.

For overclocking, where adequate cooling becomes vital, I'd go with
water cooling for the CPU. That would leave more room inside the case
for air cooling of the other components. But... that's an added expense
that one may not want to bear.

*TimDaniels*

On Sun, 19 Aug 2012 14:34:23 -0400, "
wrote:


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

You and Larkin are both idiots.

On Sun, 19 Aug 2012 13:05:25 -0700, TheGlimmerMan
wrote:

On Sun, 19 Aug 2012 14:34:23 -0400, "
wrote:


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

You and Larkin are both idiots.

From you, AlwayWrong, that's some compliment.

On Aug 18, 11:17*pm, Jeff Liebermann wrote:

What you want is immersion cooling:

I did a Google search after my post, and found that all the references
to the use of mineral oil were to immersion cooling. However, I have
also seen it noted that mineral oil could damage some parts of present-
day computers.

I was thinking in terms of avoiding immersion, but using a forced
flow.

John Savard

On 2012-08-19, Tim Williams wrote:
"Martin Brown" wrote in message
...
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.

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.

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

--
⚂⚃ 100% natural

--- Posted via news://freenews.netfront.net/ - Complaints to ---

On Sat, 18 Aug 2012 17:54:54 -0700, Quadibloc wrote:

On Aug 18, 11:19Â*am, "Skybuck Flying"
wrote:

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


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

On Sun, 19 Aug 2012 10:22:54 +0100, Martin Brown
wrote:

On 19/08/2012 05:18, John Larkin wrote:
On Sat, 18 Aug 2012 17:19:48 -0700 (PDT), Robert Macy
wrote:

On Aug 18, 12:59 pm, John Larkin
wrote:
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,

Minimum theta would do.


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. .

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

It's not. Look at a heatsink theta-versus-air-flow curve. There's also
cooling at zero flow.


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 don't think the experiment is easy. With the same fan, you'd have to
vary the airflow resistance, like the pin or fin density or something,
and keep the remaining geometry the same.

This would matter in a case like deciding between two heatsinks that
are the same overall dimensions but have different fin densities,
cooled by the same fan. Heatsink data sheets give you half the
information you need (theta vs flow) but not the other half
(backpressure vs flow).



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.

I wonder if CPU chip layouts include hot-spot distribution, like
putting the hottest bits into the corners or something.