CPU Cooler designs?

Hi,

As I understand it, most ATX style PC setups have a fan above the CPU
that blows air down onto the CPU to keep it cool, and the hot air
bounces around inside the PC case until it can find an exit (if it's lucky).

As I see it, there are two problems with this,

a) unless you have a vent in the side of the PC case, the air being
taken in by the CPU cooler will not be cool, because it's air from
inside the PC case?

b) the hot air from the bottom of the heat sink ends up warming up the
Motherboard?

I was looking at the Dell CPU coolers of the GX280, GX620 workstaions
(Intel P4 / Pentium D) and the PE2400, PE 2600, PE2800 servers (Intel
Xeon). The design is completely different. The air is sucked in from the
front of the case, straight over the CPU and out of the back - how cool
is that? Pretty cool, and there's hardly any noise either.

--
Gerry_uk

Gerry_uk wrote

As I understand it, most ATX style PC setups have a fan above the CPU that blows air down onto the
CPU to keep it cool, and the hot air
bounces around inside the PC case until it can find an exit (if it's lucky).

No luck involved, there is normally at least the power supply
fan than moves the air inside the case to outside the case.

As I see it, there are two problems with this,

a) unless you have a vent in the side of the PC case, the air being taken in by the CPU cooler
will not be cool, because it's air from inside the PC case?

Quite a few of the later cases have a duct
that supplys outside air to the cpu and fan.

b) the hot air from the bottom of the heat sink ends up warming up the Motherboard?

In practice that really doesnt produce much of a problem.

I was looking at the Dell CPU coolers of the GX280, GX620 workstaions
(Intel P4 / Pentium D) and the PE2400, PE 2600, PE2800 servers (Intel
Xeon). The design is completely different. The air is sucked in from
the front of the case, straight over the CPU and out of the back -
how cool is that? Pretty cool, and there's hardly any noise either.

Its just one way of doing things.

the dell solution is the BX rather than the ATX cooling

-john

"Rod Speed" wrote in message
...
Gerry_uk wrote

As I understand it, most ATX style PC setups have a fan above the CPU
that blows air down onto the CPU to keep it cool, and the hot air
bounces around inside the PC case until it can find an exit (if it's
lucky).

No luck involved, there is normally at least the power supply
fan than moves the air inside the case to outside the case.

As I see it, there are two problems with this,

a) unless you have a vent in the side of the PC case, the air being taken
in by the CPU cooler will not be cool, because it's air from inside the
PC case?

Quite a few of the later cases have a duct
that supplys outside air to the cpu and fan.

b) the hot air from the bottom of the heat sink ends up warming up the
Motherboard?

In practice that really doesnt produce much of a problem.

I was looking at the Dell CPU coolers of the GX280, GX620 workstaions
(Intel P4 / Pentium D) and the PE2400, PE 2600, PE2800 servers (Intel
Xeon). The design is completely different. The air is sucked in from
the front of the case, straight over the CPU and out of the back -
how cool is that? Pretty cool, and there's hardly any noise either.

Its just one way of doing things.

"Gerry_uk" wrote in message
...
Hi,

As I understand it, most ATX style PC setups have a fan above the CPU
that blows air down onto the CPU to keep it cool, and the hot air
bounces around inside the PC case until it can find an exit (if it's
lucky).

As I see it, there are two problems with this,

a) unless you have a vent in the side of the PC case, the air being
taken in by the CPU cooler will not be cool, because it's air from
inside the PC case?

b) the hot air from the bottom of the heat sink ends up warming up the
Motherboard?

I was looking at the Dell CPU coolers of the GX280, GX620 workstaions
(Intel P4 / Pentium D) and the PE2400, PE 2600, PE2800 servers (Intel
Xeon). The design is completely different. The air is sucked in from the
front of the case, straight over the CPU and out of the back - how cool
is that? Pretty cool, and there's hardly any noise either.

--
Gerry_uk

My Gigabyte Aurora pulls air in from front bottom via 120mm fan and then
expels it from the back via two 120mm fans at middle and top of chassis.
Now, if I position the Zalman 9500 so that its fan intake side is parallel
to the front of the case(facing it), then the CPU cooler should actually
help facilitate the cooling air flow as the external air is pulled in from
front bottom, passed through the CPU cooler fan/fins and proceeds out the
back. No whirling flow patterns, just a nice line through the case and over
the motherboard. Only problem: My OCZ PS has a fan underneath its case
pointing downward at the mobo with another out the back. Hopefully, this
downward fan actually sucks air up through the PS box and out the back. If
so, it will probably add even more to the air evac. If not, then there's a
flow conflict. We'll see when I get it all hooked up. But there is no other
fan blowing air down from above and I've never seen any ATX case that
deliberately does this either. Only from PSUs that have bottom fans. My old
Supermicro full tower does the exact same thing. Cool air from front bottom
to exhaust fans back top. This isn't new thermal management, they've been
doing this for awhile. Even side air duct cases have been out for awhile.

Ron

On Sat, 23 Sep 2006 23:06:52 +0100, Gerry_uk
wrote:

Hi,

As I understand it, most ATX style PC setups have a fan above the CPU
that blows air down onto the CPU to keep it cool, and the hot air
bounces around inside the PC case until it can find an exit (if it's lucky).

No, a properly set up case has a bottom front intake and a
center and top rear exhaust. Heated air exhausted out of
the heatsink is moving towards the exhaust fans at all
times. A small percentage of it will get recirculated back
though the heatsink, BUT, attempts to change this will
typically reduce overall airflow, so it can have a
diminishing return (or even be worse) trying to minimize
recirculation.



As I see it, there are two problems with this,

a) unless you have a vent in the side of the PC case, the air being
taken in by the CPU cooler will not be cool, because it's air from
inside the PC case?

You do not want a vent in the side unless the entire system
is set up to still maintain reasonable airflow considering
the effect of that side vent.

Remember one very important factor in proper system setup:

Each part is supposed to have adequate heat removal method,
including sufficient 'sink. The focus is never to try to
get CPU the most air, nor most cool air. Incoming air does
as described above, comes on the bottom front and travels
towards the top rear. It is supposed to remove the heat
from the HDDs, southbridge or single-chip on motherboard,
flow by the video card, and anything else in this lower/mid
region. If you try to change this flow by drawing in air
near the CPU, you will necessarily reduce cooling of the
other parts unless other addt'l accomdations are made to
cool them.

The CPU has a huge heatsink on it, these other parts do not
(even video card, is not usually "huge" in comparison). The
other parts depend on the passive airflow while the CPU has
a fan.



b) the hot air from the bottom of the heat sink ends up warming up the
Motherboard?

It doesn't matter because:

1) The air is not extremely hot, parts that don't produce
much heat can stand to be a little warmer than they would
have been had there been no CPU heat.

2) The few parts that are warmer than this heated air, will
be cooled by it still.



I was looking at the Dell CPU coolers of the GX280, GX620 workstaions
(Intel P4 / Pentium D) and the PE2400, PE 2600, PE2800 servers (Intel
Xeon). The design is completely different.

No, the design is exactly the same, except they do without
the CPU sink fan by putting a duct on the rear.

It can be quieter, or it can be same noise level as a
well-designed system. The reason for this is that the rear
fan has to spin faster because of the snorkel, and because
you wouldn't be comparing apples:apples if only considering
systems that don't use RPM-reduced throttling of the fans as
the Dell systems typically do.

The reality is that Dell saves $1 or 2 by eliminating one
fan, but if a system is not budget constrained (or profit
maximized, however you want to look at it), the alternative
system can run cooler than Dell's can, because the rear fan
can more more air without the duct, and a heatsink with a
fan on it can have that fan running at low enough RPM that
it is not descriminable over the noise of the rear fan (what
little there is).

In the end, there is one simple truth: You have a case that
has parts producing X amount of heat. The heat buildup of
the parts inside depends on the total airflow rate in and
out of the system. When Dell uses the snorkel on the rear
fan, it has a lower airflow:noise ratio and thus, for the
given level of noise the lower airflow does not get the heat
out as fast, the chassis internal temp average is higher.

In some systems, spot-measurements of a given component will
be cooler in the Dell system. In others, warmer in the
Dell. On average, the Dell will be warmer overall, so if
you are concerned about CPU heat as it appeared when
starting your post, the most significant factor may be
whether the heatsink quality is better than Dell's or not.
It is a large market with many different 'sinks, some are
better, others are worse.

The air is sucked in from the
front of the case, straight over the CPU and out of the back - how cool
is that? Pretty cool, and there's hardly any noise either.

Cool? That's how many OEM systems have been set up for
years. If you want you can build your own like this, all
you need is to fabricate your own rear exhaust snorkel and a
suitable heatsink designed for passive cooling (typically
tall wider spaced tines instead of shorter, denser spaced
fins).

On Sat, 23 Sep 2006 22:53:24 GMT, "Major Ninth"
wrote:

the dell solution is the BX rather than the ATX cooling



On today's new systems, yes, but we have no idea which the
OP is looking at to make the observation... Dell has been
doing similar to what was described for years, as have other
OEMs.

"Gerry_uk" wrote in message
...
Hi,

As I understand it, most ATX style PC setups have a fan above the
CPU that blows air down onto the CPU to keep it cool, and the hot
air bounces around inside the PC case until it can find an exit (if
it's lucky).

As I see it, there are two problems with this,

a) unless you have a vent in the side of the PC case, the air being
taken in by the CPU cooler will not be cool, because it's air from
inside the PC case?

b) the hot air from the bottom of the heat sink ends up warming up
the Motherboard?

I was looking at the Dell CPU coolers of the GX280, GX620
workstaions (Intel P4 / Pentium D) and the PE2400, PE 2600, PE2800
servers (Intel Xeon). The design is completely different. The air is
sucked in from the front of the case, straight over the CPU and out
of the back - how cool is that? Pretty cool, and there's hardly any
noise either.


You could cut a hole in the side panel and put a shroud around the CPU
fan so fresh cooler air gets sucked in and immediately used to cool
the CPU rather than on relying on air that has entered a foot or more
away and been pre-warmed by hard drives, memory sticks, Northbridge
chip, or whatever is between the front case grill and the CPU.

"Vanguard" wrote in message
...
"Gerry_uk" wrote in message
...
Hi,

As I understand it, most ATX style PC setups have a fan above the
CPU that blows air down onto the CPU to keep it cool, and the hot
air bounces around inside the PC case until it can find an exit (if
it's lucky).

As I see it, there are two problems with this,

a) unless you have a vent in the side of the PC case, the air being
taken in by the CPU cooler will not be cool, because it's air from
inside the PC case?

b) the hot air from the bottom of the heat sink ends up warming up
the Motherboard?

I was looking at the Dell CPU coolers of the GX280, GX620
workstaions (Intel P4 / Pentium D) and the PE2400, PE 2600, PE2800
servers (Intel Xeon). The design is completely different. The air is
sucked in from the front of the case, straight over the CPU and out
of the back - how cool is that? Pretty cool, and there's hardly any
noise either.


You could cut a hole in the side panel and put a shroud around the CPU
fan so fresh cooler air gets sucked in and immediately used to cool
the CPU rather than on relying on air that has entered a foot or more
away and been pre-warmed by hard drives, memory sticks, Northbridge
chip, or whatever is between the front case grill and the CPU.


I was under the impression that you just want the hot air drawn off the
components. I'm not so sure I'd want cool air pumped over my CPU. What
happens when a cold front hits a warm front? I'm not suggesting it would
rain inside my case, but wouldn't condensation come into play? My box will
be in an AC environment and sometimes that cool air is actually cold. Now
maybe the hot components stay hot enough to evaporate that, but just to make
sure, I'll throw a couple of silicon packs in the bottom of my case. Think
that'll help? : )

Ron

"Ron Krebs" wrote in
news:GglRg.1011$fl2.452@trnddc02:

I was under the impression that you just want the hot air drawn off
the components. I'm not so sure I'd want cool air pumped over my CPU.
What happens when a cold front hits a warm front? I'm not suggesting
it would rain inside my case, but wouldn't condensation come into
play? My box will be in an AC environment and sometimes that cool air
is actually cold. Now maybe the hot components stay hot enough to
evaporate that, but just to make sure, I'll throw a couple of silicon
packs in the bottom of my case. Think that'll help? : )

When the cool air hits the warm stuff inside the case it will get warmer
and the relative humidity of that air will drop. If you had cold stuff in
the case and you were pumping warm outside air onto it then you might have
a condensation problem, as can occur with some extreme phase-change type
coolers.

--
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"Mitch Crane" -three wrote in message
.. .
"Ron Krebs" wrote in
news:GglRg.1011$fl2.452@trnddc02:

I was under the impression that you just want the hot air drawn off
the components. I'm not so sure I'd want cool air pumped over my
CPU.
What happens when a cold front hits a warm front? I'm not
suggesting
it would rain inside my case, but wouldn't condensation come into
play? My box will be in an AC environment and sometimes that cool
air
is actually cold. Now maybe the hot components stay hot enough to
evaporate that, but just to make sure, I'll throw a couple of
silicon
packs in the bottom of my case. Think that'll help? : )

When the cool air hits the warm stuff inside the case it will get
warmer
and the relative humidity of that air will drop. If you had cold
stuff in
the case and you were pumping warm outside air onto it then you
might have
a condensation problem, as can occur with some extreme phase-change
type
coolers.


Guess Ron forgot that the air is *dryer* in winter when the air is
colder hence the higher sales of humidifiers in winter. Silicon packs
are useless when air is moving. They are used in sealed containers to
remove what moisture is there and would be *trapped* there.