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Cooling CPU with passive heatsink?

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Anonymous
a b B Homebuilt system
a b à CPUs
September 5, 2004 9:30:25 PM

Archived from groups: alt.comp.hardware.pc-homebuilt,uk.comp.homebuilt (More info?)

Hi,

I'm currently getting some parts together to build a second PC, and I have a
question regarding cooling.

A bit of background.... I also have a Dell Dimension 8300, which doesn't use
the 'normal' cooling setup for the CPU of a heatsink with fan mounted on it,
but instead has a large heatsink on the CPU, and a 120mm case fan with a
duct to draw air across and away from the CPU heatsink.
It seems to work well, at least the PC hasn't gone into meltdown yet, and is
pretty quiet.

I am using an Antec case for the second PC, which has a large 120mm case
mounted fan at the back. I am considering setting up the same config. as my
Dell to cool the CPU. I would have to make a duct to attach to the case fan
to make it draw air across the CPU heatsink, but that shouldn't be too
difficult.

I've read up on this a bit and the ducted fan arrangement seems, in theory
to be better than a heatsink mounted fan, because..
a) It is bigger and can move more air
b) Being bigger it can run a little slower and therefore be quieter
c) A heatsink fan has a deadspot in the middle, where the motor hub is,
leading to inefficient cooling.

So, what do you think?

Any recommendations re. heatsinks and places to get them? (in the UK)

Oh yes, the system in question will be running an Athlon XP2500 or XP2800,
probably not overclocked.

Regards, John

More about : cooling cpu passive heatsink

Anonymous
a b B Homebuilt system
a b à CPUs
September 5, 2004 9:30:26 PM

Archived from groups: alt.comp.hardware.pc-homebuilt,uk.comp.homebuilt (More info?)

"John Fryatt" <jrf1> wrote in message
news:R2I_c.402$rO5.35@newsfe3-win.ntli.net...
> Hi,
>
> I'm currently getting some parts together to build a second PC, and I have
a
> question regarding cooling.
>
> A bit of background.... I also have a Dell Dimension 8300, which doesn't
use
> the 'normal' cooling setup for the CPU of a heatsink with fan mounted on
it,
> but instead has a large heatsink on the CPU, and a 120mm case fan with a
> duct to draw air across and away from the CPU heatsink.
> It seems to work well, at least the PC hasn't gone into meltdown yet, and
is
> pretty quiet.
>
> I am using an Antec case for the second PC, which has a large 120mm case
> mounted fan at the back. I am considering setting up the same config. as
my
> Dell to cool the CPU. I would have to make a duct to attach to the case
fan
> to make it draw air across the CPU heatsink, but that shouldn't be too
> difficult.
>
> I've read up on this a bit and the ducted fan arrangement seems, in theory
> to be better than a heatsink mounted fan, because..
> a) It is bigger and can move more air
> b) Being bigger it can run a little slower and therefore be quieter
> c) A heatsink fan has a deadspot in the middle, where the motor hub is,
> leading to inefficient cooling.
>
> So, what do you think?
>
> Any recommendations re. heatsinks and places to get them? (in the UK)
>
> Oh yes, the system in question will be running an Athlon XP2500 or XP2800,
> probably not overclocked.
>
> Regards, John
>

For the time, effort, and (possibly money) involved, it might be better to
look into watercooling. -Dave
Anonymous
a b B Homebuilt system
a b à CPUs
September 6, 2004 12:39:16 AM

Archived from groups: alt.comp.hardware.pc-homebuilt,uk.comp.homebuilt (More info?)

John Fryatt wrote:
>
> Hi,
>
> I'm currently getting some parts together to build a second PC, and I have a
> question regarding cooling.
>
> A bit of background.... I also have a Dell Dimension 8300, which doesn't use
> the 'normal' cooling setup for the CPU of a heatsink with fan mounted on it,
> but instead has a large heatsink on the CPU, and a 120mm case fan with a
> duct to draw air across and away from the CPU heatsink.
> It seems to work well, at least the PC hasn't gone into meltdown yet, and is
> pretty quiet.
>
> I am using an Antec case for the second PC, which has a large 120mm case
> mounted fan at the back. I am considering setting up the same config. as my
> Dell to cool the CPU. I would have to make a duct to attach to the case fan
> to make it draw air across the CPU heatsink, but that shouldn't be too
> difficult.
>
> I've read up on this a bit and the ducted fan arrangement seems, in theory
> to be better than a heatsink mounted fan, because..
> a) It is bigger and can move more air
> b) Being bigger it can run a little slower and therefore be quieter
> c) A heatsink fan has a deadspot in the middle, where the motor hub is,
> leading to inefficient cooling.
>
> So, what do you think?

Im' using a ducted fan for a P4 Northwood build. You could use a huge
gigantic heatsink and it could possibly be passive. The problem is
attaching a large weight to the CPU and make the installation stable.
Intel specifies a weight limit on HS+fan of 450 gr. The Zalman duct
fan that I use is 500 gr with fan, so it's just about the limit. I know
that you'll be running an AMD processor, but similar considerations may
apply.
Related resources
Anonymous
a b B Homebuilt system
a b à CPUs
September 6, 2004 1:31:15 AM

Archived from groups: alt.comp.hardware.pc-homebuilt,uk.comp.homebuilt (More info?)

["Followup-To:" header set to uk.comp.homebuilt.]
John Fryatt was seen penning the following ode to ... whatever:
> Hi,
>
> I'm currently getting some parts together to build a second PC, and I have a
> question regarding cooling.
>
> A bit of background.... I also have a Dell Dimension 8300, which doesn't use
> the 'normal' cooling setup for the CPU of a heatsink with fan mounted on it,
> but instead has a large heatsink on the CPU, and a 120mm case fan with a
> duct to draw air across and away from the CPU heatsink.
> It seems to work well, at least the PC hasn't gone into meltdown yet, and is
> pretty quiet.

Compaq at least used to use similar arrangements in their SFF (small
form factor) machines, and they tend to be fairly quiet.

> I am using an Antec case for the second PC, which has a large 120mm case
> mounted fan at the back. I am considering setting up the same config. as my
> Dell to cool the CPU. I would have to make a duct to attach to the case fan
> to make it draw air across the CPU heatsink, but that shouldn't be too
> difficult.
>
> I've read up on this a bit and the ducted fan arrangement seems, in theory
> to be better than a heatsink mounted fan, because..
> a) It is bigger and can move more air
> b) Being bigger it can run a little slower and therefore be quieter

(a) and (b) of course are somewhat exclusive. How far away is the fan
from the CPU?

> c) A heatsink fan has a deadspot in the middle, where the motor hub is,
> leading to inefficient cooling.

Yes, but that's mostly becoming an issue if you absolutely need to
squeeze the last drop of cooling ability out of your HSF.

> So, what do you think?
>
> Any recommendations re. heatsinks and places to get them? (in the UK)

Depends on the orientation of the heatsink re the fan - you'd want
something with as much surface area as possible. Something like a
Zalman flower cooler maybe, but you'd need to make sure that air gets
drawn through the fins, not over the cooler.
--
My quiet computing page:
http://www.unixconsult.co.uk/computing/quiet-pc-howto.h...
Anonymous
a b B Homebuilt system
a b à CPUs
September 6, 2004 2:35:45 AM

Archived from groups: alt.comp.hardware.pc-homebuilt,uk.comp.homebuilt (More info?)

"John Fryatt" <jrf1@ntlworld.com> wrote:

>A bit of background.... I also have a Dell Dimension 8300, which doesn't use
>the 'normal' cooling setup for the CPU of a heatsink with fan mounted on it,
>but instead has a large heatsink on the CPU, and a 120mm case fan with a
>duct to draw air across and away from the CPU heatsink.
>It seems to work well, at least the PC hasn't gone into meltdown yet, and is
>pretty quiet.

<snip>

>I've read up on this a bit and the ducted fan arrangement seems, in theory
>to be better than a heatsink mounted fan, because..
>a) It is bigger and can move more air
>b) Being bigger it can run a little slower and therefore be quieter
>c) A heatsink fan has a deadspot in the middle, where the motor hub is,
>leading to inefficient cooling.

>So, what do you think?

Very common in machines built by larger OEMs, such as Dell, HP/Compaq
etc. Generally very effective and much quieter than the "let's stick
this bloody aircraft turbine on this cheap nasty metal block" approach
favoured by retail and after-market coolers.

>Any recommendations re. heatsinks and places to get them? (in the UK)

I believe Dell use Coolermaster heat sinks in some of their machines
coupled with a custom duct designs. AFAIK the same solutions aren't
available retail as they need to be integrated with the case to work
properly. You could probably pick suitable OEM parts from spares
stockists or eBay, although they tend to be for P4 chips as they're
dominant in the "branded" market.

>Oh yes, the system in question will be running an Athlon XP2500 or XP2800,
>probably not overclocked.

Only ever seen these solutions used on Intel chips which, as a general
rule, don't require quite as much cooling. That said, now Prescott is
with us the OEMs will almost certainly of had to re-design their
cooling solution to cope. I've not taken a recent machine apart to
see if they're still using the same fan/duct approach.

The only OEM machine I came across using an AMD chip used the more
"conventional" cooler which might imply they couldn't get sufficient
cooling using the kind of solution you're looking to use but that's
not to say it can't be done.


--
>iv< Paul >iv<
Anonymous
a b B Homebuilt system
a b à CPUs
September 6, 2004 2:50:13 AM

Archived from groups: alt.comp.hardware.pc-homebuilt,uk.comp.homebuilt (More info?)

John Fryatt wrote:
> Hi,
>
> I'm currently getting some parts together to build a second PC, and I
> have a question regarding cooling.
<...>
> I am using an Antec case for the second PC, which has a large 120mm
> case mounted fan at the back. I am considering setting up the same
> config. as my Dell to cool the CPU. I would have to make a duct to
> attach to the case fan to make it draw air across the CPU heatsink,
> but that shouldn't be too difficult.
>
> I've read up on this a bit and the ducted fan arrangement seems, in
> theory to be better than a heatsink mounted fan, because..
> a) It is bigger and can move more air
> b) Being bigger it can run a little slower and therefore be quieter
> c) A heatsink fan has a deadspot in the middle, where the motor hub
> is, leading to inefficient cooling.
>
> So, what do you think?

I am a duct enthusiast (I couldn't say fan, could I?) and I wrote up an
article on my website in the 'Miscellanea' section about 'Recent
xp1800+ build' as it was at the time. [It's now a xp3200+ !]

>
> Oh yes, the system in question will be running an Athlon XP2500 or
> XP2800, probably not overclocked.

Get the mobile XP-M2500+ which runs cooler and is unlocked.

HTH
--
Graham W http://www.gcw.org.uk/ PGM-FI page updated, Graphics Tutorial
WIMBORNE http://www.wessex-astro-society.freeserve.co.uk/ Wessex
Dorset UK Astro Society's Web pages, Info, Meeting Dates, Sites & Maps
Change 'news' to 'sewn' in my Reply address to avoid my spam filter.
Anonymous
a b B Homebuilt system
a b à CPUs
September 6, 2004 2:33:15 PM

Archived from groups: alt.comp.hardware.pc-homebuilt,uk.comp.homebuilt (More info?)

"Paul Hopwood" <paul@hopwood.org.uk> wrote in message
news:ar0nj01e44k0b4n3b1g93plvv4sqdqmqri@4ax.com...
> "John Fryatt" <jrf1@ntlworld.com> wrote:
> >A bit of background.... I also have a Dell Dimension 8300, which doesn't
> >use the 'normal' cooling setup for the CPU of a heatsink with fan mounted
> >on it, but instead has a large heatsink on the CPU, and a 120mm case fan
> >with a duct to draw air across and away from the CPU heatsink.
[snip]
> Only ever seen these solutions used on Intel chips which, as a general
> rule, don't require quite as much cooling.

Now come on Paul, you know better than that. The difference between AMD and
Intel's mainstream chips (in processing power vs dissipated power) became
pretty small when the P4 first appeared, and has certainly been small enough
to be ignored for a couple of years.

Alex
Anonymous
a b B Homebuilt system
a b à CPUs
September 6, 2004 3:44:10 PM

Archived from groups: alt.comp.hardware.pc-homebuilt,uk.comp.homebuilt (More info?)

> Only ever seen these solutions used on Intel chips which, as a general
> rule, don't require quite as much cooling. That said, now Prescott is
> with us the OEMs will almost certainly of had to re-design their
> cooling solution to cope. I've not taken a recent machine apart to
> see if they're still using the same fan/duct approach.

My Dell machine, which is the ducted cooling machine referred to earlier,
uses a Prescott.
Anonymous
a b B Homebuilt system
a b à CPUs
September 6, 2004 3:47:55 PM

Archived from groups: alt.comp.hardware.pc-homebuilt,uk.comp.homebuilt (More info?)

Hi Graham,

Took a look at your Web page. Excellent, and it reinforced my plan to go the
duct route.
I am not obsessive about it but the idea of lots of roaring fans is not a
good thing, for me.

I saw a PC for sale on eBay recently which purported to have 12 fans! The
thing must sound like a Bell Jetranger when it starts up! :-(

Regards, John


"Graham W" <graham@his.com.puter.INVALID> wrote in message
news:413b8eb8$0$75650$ed2e19e4@ptn-nntp-reader04.plus.net...
> John Fryatt wrote:
> > Hi,
> >
> > I'm currently getting some parts together to build a second PC, and I
> > have a question regarding cooling.
> <...>
> > I am using an Antec case for the second PC, which has a large 120mm
> > case mounted fan at the back. I am considering setting up the same
> > config. as my Dell to cool the CPU. I would have to make a duct to
> > attach to the case fan to make it draw air across the CPU heatsink,
> > but that shouldn't be too difficult.
> >
> > I've read up on this a bit and the ducted fan arrangement seems, in
> > theory to be better than a heatsink mounted fan, because..
> > a) It is bigger and can move more air
> > b) Being bigger it can run a little slower and therefore be quieter
> > c) A heatsink fan has a deadspot in the middle, where the motor hub
> > is, leading to inefficient cooling.
> >
> > So, what do you think?
>
> I am a duct enthusiast (I couldn't say fan, could I?) and I wrote up an
> article on my website in the 'Miscellanea' section about 'Recent
> xp1800+ build' as it was at the time. [It's now a xp3200+ !]
>
> >
> > Oh yes, the system in question will be running an Athlon XP2500 or
> > XP2800, probably not overclocked.
>
> Get the mobile XP-M2500+ which runs cooler and is unlocked.
>
> HTH
> --
> Graham W http://www.gcw.org.uk/ PGM-FI page updated, Graphics Tutorial
> WIMBORNE http://www.wessex-astro-society.freeserve.co.uk/ Wessex
> Dorset UK Astro Society's Web pages, Info, Meeting Dates, Sites & Maps
> Change 'news' to 'sewn' in my Reply address to avoid my spam filter.
Anonymous
a b B Homebuilt system
a b à CPUs
September 6, 2004 3:54:59 PM

Archived from groups: alt.comp.hardware.pc-homebuilt,uk.comp.homebuilt (More info?)

Thanks all for the advice. I kind of expected to get replies saying "don't
be stupid, use the fan/heatsink", so I am quite gratified to see some
positive remarks.
I think I'll give the duct and passive heatsink a try. I like my new Dell
for its relative quietness, and I'll try to get similar levels from the
second machine. Unfortunatley I've ended up with a Radeon graphics card*
which does have a small fan. Can't win 'em all I suppose. ;-)
Maybe I'll try taking off the fan and attaching a larger heatsink, but
that's one for the future, once I get the box up and working.

John

* - not an issue with the Dell as it isn't a gaming box so I'm using a
Matrox card which doesn't need a fan.


"John Fryatt" <jrf1@ntlworld.com> wrote in message
news:R2I_c.402$rO5.35@newsfe3-win.ntli.net...
> Hi,
>
> I'm currently getting some parts together to build a second PC, and I have
a
> question regarding cooling.
>
> A bit of background.... I also have a Dell Dimension 8300, which doesn't
use
> the 'normal' cooling setup for the CPU of a heatsink with fan mounted on
it,
> but instead has a large heatsink on the CPU, and a 120mm case fan with a
> duct to draw air across and away from the CPU heatsink.
> It seems to work well, at least the PC hasn't gone into meltdown yet, and
is
> pretty quiet.
>
> I am using an Antec case for the second PC, which has a large 120mm case
> mounted fan at the back. I am considering setting up the same config. as
my
> Dell to cool the CPU. I would have to make a duct to attach to the case
fan
> to make it draw air across the CPU heatsink, but that shouldn't be too
> difficult.
>
> I've read up on this a bit and the ducted fan arrangement seems, in theory
> to be better than a heatsink mounted fan, because..
> a) It is bigger and can move more air
> b) Being bigger it can run a little slower and therefore be quieter
> c) A heatsink fan has a deadspot in the middle, where the motor hub is,
> leading to inefficient cooling.
>
> So, what do you think?
Anonymous
a b B Homebuilt system
a b à CPUs
September 6, 2004 3:55:00 PM

Archived from groups: alt.comp.hardware.pc-homebuilt,uk.comp.homebuilt (More info?)

John Fryatt wrote:

> Thanks all for the advice. I kind of expected to get replies saying "don't
> be stupid, use the fan/heatsink", so I am quite gratified to see some
> positive remarks.
> I think I'll give the duct and passive heatsink a try. I like my new Dell
> for its relative quietness, and I'll try to get similar levels from the
> second machine.

The secret to the thing is getting the air to flow where it needs to, which
sounds simpler than it is.

For example, blowing air down onto a heatsink forces the air in that
direction (an obvious observation) but pulling air over it means the air
will follow the path of least resistance which, left to it's own
predilection, is almost never through the heatsink; hence the duct and it's
particular configuration. That also impacts the physical design of the heat
sink.

In a nutshell, a typical ducting arrangement will have some 'inlet' to the
heatsink with the heatsink shrouded by the duct to force the air to flow
along it's surfaces.

Problems include flow resistance from the duct itself (walls), and the
distance the air must flow through this 'pipe'; plus, axial fans are better
at 'blowing' than 'pulling' air. Those two often offset any 'improvement'
one envisions may result from not having fan 'dead spots' and the like.

Something people don't always think of, off the top of their head, is that
the shape of the duct also impacts noise. A round hose, typical for home
builders because it's easy, lends an amplified hollow 'rushing' sound
that's quite noticeable, and familiar if you think about it: turn on your
car heater blower. A rectangular duct helps break up internal resonances
and dampen sound reflections, as do bends and internal baffles. They also
add more flow resistance.

From a noise aspect the best place for the fan would be in the 'middle'
somewhere so it's inlet and outlet are both baffled from the outside world,
but there just isn't the room in a normal ATX case for that. Apple does it
that way in at least one of their machines though, and for that reason:
dern near silent.


> Unfortunatley I've ended up with a Radeon graphics card*
> which does have a small fan. Can't win 'em all I suppose. ;-)
> Maybe I'll try taking off the fan and attaching a larger heatsink, but
> that's one for the future, once I get the box up and working.
>
> John
>
> * - not an issue with the Dell as it isn't a gaming box so I'm using a
> Matrox card which doesn't need a fan.
>
>
Anonymous
a b B Homebuilt system
a b à CPUs
September 6, 2004 6:43:29 PM

Archived from groups: alt.comp.hardware.pc-homebuilt,uk.comp.homebuilt (More info?)

John Fryatt wrote:
[...]
> Unfortunatley I've ended up with a Radeon
> graphics card which does have a small fan. Can't win 'em all I
> suppose. ;-)
> Maybe I'll try taking off the fan and attaching a larger heatsink, but
> that's one for the future, once I get the box up and working.

If the Radeon has a thin plate (with a large hole in the middle to let air
in) covering the heatsink fins secured with some tiny cross-headed
screws, take it off!

The edge of the hole is probably too close to the tips of the fan's blades
and is generating high-frequency zizzing from the tip vortices. You'll
likely
find that the plate is mainly decorative rather than a necessary element
in the air flow design. I did this with my GF4 - Ti and it made a very
acceptable improvement.


--
Graham W http://www.gcw.org.uk/ PGM-FI page updated, Graphics Tutorial
WIMBORNE http://www.wessex-astro-society.freeserve.co.uk/ Wessex
Dorset UK Astro Society's Web pages, Info, Meeting Dates, Sites & Maps
Change 'news' to 'sewn' in my Reply address to avoid my spam filter.
Anonymous
a b B Homebuilt system
a b à CPUs
September 6, 2004 8:20:43 PM

Archived from groups: alt.comp.hardware.pc-homebuilt,uk.comp.homebuilt (More info?)

"David Maynard" <dNOTmayn@ev1.net> wrote in message
news:10jp1jpr9te0v88@corp.supernews.com...
> John Fryatt wrote:
>
> > Thanks all for the advice. I kind of expected to get replies saying
"don't
> > be stupid, use the fan/heatsink", so I am quite gratified to see some
> > positive remarks.
> > I think I'll give the duct and passive heatsink a try. I like my new
Dell
> > for its relative quietness, and I'll try to get similar levels from the
> > second machine.
>
> The secret to the thing is getting the air to flow where it needs to,
which
> sounds simpler than it is.
>
> For example, blowing air down onto a heatsink forces the air in that
> direction (an obvious observation) but pulling air over it means the air
> will follow the path of least resistance which, left to it's own
> predilection, is almost never through the heatsink; hence the duct and
it's
> particular configuration. That also impacts the physical design of the
heat
> sink.
>
> In a nutshell, a typical ducting arrangement will have some 'inlet' to the
> heatsink with the heatsink shrouded by the duct to force the air to flow
> along it's surfaces.

Yes, my Dell is like that. The duct goes right over the heatsink.

> Problems include flow resistance from the duct itself (walls), and the
> distance the air must flow through this 'pipe'; plus, axial fans are
better
> at 'blowing' than 'pulling' air. Those two often offset any 'improvement'
> one envisions may result from not having fan 'dead spots' and the like.
>
> Something people don't always think of, off the top of their head, is that
> the shape of the duct also impacts noise. A round hose, typical for home
> builders because it's easy, lends an amplified hollow 'rushing' sound
> that's quite noticeable, and familiar if you think about it: turn on your
> car heater blower. A rectangular duct helps break up internal resonances
> and dampen sound reflections, as do bends and internal baffles. They also
> add more flow resistance.

Again, the Dell has a rectangular duct. I am planning to use that as a
guide.
Thinking off the top of my head (not finalised yet) I'd probably make the
duct from plastic sheet, folded appropriately and joined.
That's a good point though re. sound effects of different shapes.
Anonymous
a b B Homebuilt system
a b à CPUs
September 7, 2004 1:54:30 AM

Archived from groups: alt.comp.hardware.pc-homebuilt,uk.comp.homebuilt (More info?)

John Fryatt wrote:

> "David Maynard" <dNOTmayn@ev1.net> wrote in message
> news:10jp1jpr9te0v88@corp.supernews.com...
>
>>John Fryatt wrote:
>>
>>
>>>Thanks all for the advice. I kind of expected to get replies saying
>
> "don't
>
>>>be stupid, use the fan/heatsink", so I am quite gratified to see some
>>>positive remarks.
>>>I think I'll give the duct and passive heatsink a try. I like my new
>
> Dell
>
>>>for its relative quietness, and I'll try to get similar levels from the
>>>second machine.
>>
>>The secret to the thing is getting the air to flow where it needs to,
>
> which
>
>>sounds simpler than it is.
>>
>>For example, blowing air down onto a heatsink forces the air in that
>>direction (an obvious observation) but pulling air over it means the air
>>will follow the path of least resistance which, left to it's own
>>predilection, is almost never through the heatsink; hence the duct and
>
> it's
>
>>particular configuration. That also impacts the physical design of the
>
> heat
>
>>sink.
>>
>>In a nutshell, a typical ducting arrangement will have some 'inlet' to the
>>heatsink with the heatsink shrouded by the duct to force the air to flow
>>along it's surfaces.
>
>
> Yes, my Dell is like that. The duct goes right over the heatsink.

Yeah, I've seen a few of the Dell internals. Nice and simple.

The Compaq AP550 dual P-III is an interesting whole system ducting setup
(completely custom) from front PSU inlet, across the dual CPUs, through the
drives, into the Mobo area, and then out the back. Can barely tell it's on
even in a dead silent room.


>>Problems include flow resistance from the duct itself (walls), and the
>>distance the air must flow through this 'pipe'; plus, axial fans are
>
> better
>
>>at 'blowing' than 'pulling' air. Those two often offset any 'improvement'
>>one envisions may result from not having fan 'dead spots' and the like.
>>
>>Something people don't always think of, off the top of their head, is that
>>the shape of the duct also impacts noise. A round hose, typical for home
>>builders because it's easy, lends an amplified hollow 'rushing' sound
>>that's quite noticeable, and familiar if you think about it: turn on your
>>car heater blower. A rectangular duct helps break up internal resonances
>>and dampen sound reflections, as do bends and internal baffles. They also
>>add more flow resistance.
>
>
> Again, the Dell has a rectangular duct. I am planning to use that as a
> guide.
> Thinking off the top of my head (not finalised yet) I'd probably make the
> duct from plastic sheet, folded appropriately and joined.
> That's a good point though re. sound effects of different shapes.

Why not plain old paperboard? Probably doesn't reflect sound as well as the
plastic and even easier to work with.
Anonymous
a b B Homebuilt system
a b à CPUs
September 7, 2004 9:30:19 PM

Archived from groups: alt.comp.hardware.pc-homebuilt,uk.comp.homebuilt (More info?)

Passive cooling is not difficult. But firsto learn the
'simple multiplication' formulas and relationships. Learn the
"degrees C per watt" rating for a heatsink. Serious heatsink
manufacturers should provide a chart that related that "degree
C per watt" number to an LFM number - the speed that air moves
through that CPU. More LFM lowers the "degree C per watt"
parameter. An exponential relationship exists between
heatsink thermal resistance and airflow speed.

Yes, a ducted fan with more CFMs can increase the LFM across
the heatsink. But as charts will demonstrate, the "degree C
per watt" parameter will decrease less as more air is moved.

This is the point: first do simple theoretical (arithmetic)
analysis. Then confirm that design with a real world example
and measurement devices (ie thermometer). When done, the room
can be at 38 degrees C and still processor does not exceed
manufacturer temperature limits. Better with a 5 degree
safety margin.

Manufacturers who want professional customers and therefore
provide those numbers, the charts, and tutorials on heatsink
design:
http://www.wakefield.com
http://www.aavidthermalloy.com

Manufacturer of fans who provides numbers and charts so help
select a fan or determine what currently exists:
http://www.comairrotron.com

Lastly - I applaud you for doing what every computer builder
should do - learn the whys and hows of computer design and
assembly. Design using the numbers rather than just echo
traditional beliefs.

John Fryatt wrote:
> ...
> Yes, my Dell is like that. The duct goes right over the heatsink.
>
>> Problems include flow resistance from the duct itself (walls),
>> and the distance the air must flow through this 'pipe'; plus,
>> axial fans are better at 'blowing' than 'pulling' air. Those
>> two often offset any 'improvement' one envisions may result
>> from not having fan 'dead spots' and the like.
>>
>> Something people don't always think of, off the top of their
>> head, is that the shape of the duct also impacts noise. A round
>> hose, typical for home builders because it's easy, lends an
>> amplified hollow 'rushing' sound that's quite noticeable, and
>> familiar if you think about it: turn on your car heater blower.
>> A rectangular duct helps break up internal resonances and dampen
>> sound reflections, as do bends and internal baffles. They also
>> add more flow resistance.
>
> Again, the Dell has a rectangular duct. I am planning to use that
> as a guide. Thinking off the top of my head (not finalised yet)
> I'd probably make the duct from plastic sheet, folded appropriately
> and joined. That's a good point though re. sound effects of
> different shapes.
September 8, 2004 2:53:21 PM

Archived from groups: alt.comp.hardware.pc-homebuilt (More info?)

On Sun, 05 Sep 2004 17:30:25 GMT, "John Fryatt" <jrf1@ntlworld.com>
wrote:

>I'm currently getting some parts together to build a second PC, and I have a
>question regarding cooling. ...

> Dell Dimension 8300, which doesn't use
>the 'normal' cooling setup for the CPU of a heatsink with fan mounted on it,
>but instead has a large heatsink on the CPU, and a 120mm case fan with a
>duct to draw air across and away from the CPU heatsink.
>..... is pretty quiet....
>
> make a duct to attach to the case fan
>to make it draw air across the CPU heatsink, but that shouldn't be too
>difficult.....
>
>I've read up on this a bit and the ducted fan arrangement seems, in theory
>to be better than a heatsink mounted fan, because..
>a) It is bigger and can move more air
>b) Being bigger it can run a little slower and therefore be quieter
>c) A heatsink fan has a deadspot in the middle, where the motor hub is,
>leading to inefficient cooling.
>
>So, what do you think?

>Oh yes, the system in question will be running an Athlon XP2500 or XP2800,
>probably not overclocked.

Thermal Power dissipation of that CPUs : around 60-70W
/maybe getting a mobile version of that Cpu for having a third less
power consumption would be a good idea even if they are a bit pricier/

Big companies like Dell have an equipe of staff
to engineer & design an efficiently AirFlow thru case /different types
& setups/ and cooling arrangements, because of doing that good is
quite a time consuming job for an individual & a lot of
experimenting!!!

You can believe me, because I have made it by myself thru time for my
setup running 7 fans in total, but all of them running around 5V &
silent! & in my case there is practically no difference with
temperatures if I have the case opened or closed (believe it or not &
it means excelent air flow!); but my setup has only half of Thermal
Power dissipation than your planned! ...

In your place I would mount together the PC using also bigger HS with
bigger & slower fans & run them on reduced voltage + a quality
designed case with a god probably (overrated) 2-fan PSU with regulated
fan RPMs & self thermocontroled too ...

Full "ducting" in really not necessary; some hard cardBoard paper may
be useful to make some "flaps type" air directors to enhance fluid
airFlow thru the case & reducing fan speeds @ 2/3 (7V!) IMHO would be
enough for your setup!

There are a lot of different mods explained to silence down PCs on the
Web; a lot of times there is no need for much extra spending but
instead a lot of using "common sense" with a bit of thinking before
starting a job! Expensive & cheap does not mean always best & worst!

You can also browse thru my site & DL it for later viewing & studying
a bit; IMHO you can get some ideas there ... / I know, I know, I did
not updated it for awhile & is not completed like it should be/...

IMHO with these days "powerfull" CPUs, I do not recommend trying
making a fanless air Cpu cooling at home; running minimum a bigger fan
@ 5V on its bigger HS is a better solution. (see the temps-my
experiment under Comp/benches ...)

good luck!
--
Regards, SPAJKY ®
& visit my site @ http://www.spajky.vze.com
"Tualatin OC-ed / BX-Slot1 / inaudible setup!"
E-mail AntiSpam: remove ##
Anonymous
a b B Homebuilt system
a b à CPUs
September 8, 2004 5:33:01 PM

Archived from groups: alt.comp.hardware.pc-homebuilt (More info?)

> In your place I would mount together the PC using also bigger HS with
> bigger & slower fans & run them on reduced voltage + a quality
> designed case with a god probably (overrated) 2-fan PSU with regulated
> fan RPMs & self thermocontroled too ...
>
> Full "ducting" in really not necessary; some hard cardBoard paper may
> be useful to make some "flaps type" air directors to enhance fluid
> airFlow thru the case & reducing fan speeds @ 2/3 (7V!) IMHO would be
> enough for your setup!

> IMHO with these days "powerfull" CPUs, I do not recommend trying
> making a fanless air Cpu cooling at home; running minimum a bigger fan
> @ 5V on its bigger HS is a better solution. (see the temps-my
> experiment under Comp/benches ...)

Thanks for the advice. I'll certainly look at your site.

As I see it I am not proposing fanless cooling for the CPU, but rather a
setup where the fan is not mounted directly on top of the heat sink. That
way, as you say, it can be bigger and run slower. The duct is to connect the
fan to the heat sink, in effect. Also, the remote fan will dump the warmed
air outside the cas, rahter than just circulate it inside, and also double
up as general ventialtion device for the whole PC.

I think this whole issue is not that simple, and needs a bit of thinking
about, including doing a few calculations, as w_tom suggested.
Plan A is to get the PC built and running using the supplied heatsink fan
from AMD. Plan B will then be to look at the ducting etc. as discussed here.

Interestingly, my Dell started to acclerate it's fan a couple of times the
other day, making me think about that.
I'm tempted to see what I can do there to improve cooling. Initial thoughts
are to...
1) lap the heatsink and put it back on with good thermal compund (e.g.
'Arctic Silver')
2) make an extra vents in the front of the case (this is a Dell Dimension
8300, and the new 8400 has the same case design except for an additional
vent in the front for "improved cooling" - admittedly for faster 3.4GHz
CPUs)

Thanks for all your advice everyone, it's been illuminating.

Regards, John
Anonymous
a b B Homebuilt system
a b à CPUs
September 8, 2004 6:12:09 PM

Archived from groups: alt.comp.hardware.pc-homebuilt,uk.comp.homebuilt (More info?)

w_tom wrote:
> Passive cooling is not difficult. But firsto learn the
> 'simple multiplication' formulas and relationships. Learn the
> "degrees C per watt" rating for a heatsink. Serious heatsink
> manufacturers should provide a chart that related that "degree
> C per watt" number to an LFM number - the speed that air moves
> through that CPU.

Ari doesn't move through a CPU, electricity does. Did you mean heatsink?


> More LFM lowers the "degree C per watt"
> parameter. An exponential relationship exists between
> heatsink thermal resistance and airflow speed.
>
> Yes, a ducted fan with more CFMs can increase the LFM across
> the heatsink. But as charts will demonstrate, the "degree C
> per watt" parameter will decrease less as more air is moved.
>
> This is the point: first do simple theoretical (arithmetic)
> analysis. Then confirm that design with a real world example
> and measurement devices (ie thermometer). When done, the room
> can be at 38 degrees C and still processor does not exceed
> manufacturer temperature limits. Better with a 5 degree
> safety margin.
>
> Manufacturers who want professional customers and therefore
> provide those numbers, the charts, and tutorials on heatsink
> design:
> http://www.wakefield.com
> http://www.aavidthermalloy.com
>
> Manufacturer of fans who provides numbers and charts so help
> select a fan or determine what currently exists:
> http://www.comairrotron.com
>
> Lastly - I applaud you for doing what every computer builder
> should do - learn the whys and hows of computer design and
> assembly. Design using the numbers rather than just echo
> traditional beliefs.
>
> John Fryatt wrote:
>
>>...
>>Yes, my Dell is like that. The duct goes right over the heatsink.
>>
>>
>>>Problems include flow resistance from the duct itself (walls),
>>>and the distance the air must flow through this 'pipe'; plus,
>>>axial fans are better at 'blowing' than 'pulling' air. Those
>>>two often offset any 'improvement' one envisions may result
>>>from not having fan 'dead spots' and the like.
>>>
>>>Something people don't always think of, off the top of their
>>>head, is that the shape of the duct also impacts noise. A round
>>>hose, typical for home builders because it's easy, lends an
>>>amplified hollow 'rushing' sound that's quite noticeable, and
>>>familiar if you think about it: turn on your car heater blower.
>>>A rectangular duct helps break up internal resonances and dampen
>>>sound reflections, as do bends and internal baffles. They also
>>>add more flow resistance.
>>
>>Again, the Dell has a rectangular duct. I am planning to use that
>>as a guide. Thinking off the top of my head (not finalised yet)
>>I'd probably make the duct from plastic sheet, folded appropriately
>>and joined. That's a good point though re. sound effects of
>>different shapes.


--
spammage trappage: replace fishies_ with yahoo
Anonymous
a b B Homebuilt system
a b à CPUs
September 8, 2004 6:12:10 PM

Archived from groups: alt.comp.hardware.pc-homebuilt,uk.comp.homebuilt (More info?)

"spodosaurus" <spodosaurus@_yahoo_.com> wrote in message
news:413ea38c$1@quokka.wn.com.au...
> w_tom wrote:
> > Passive cooling is not difficult. But firsto learn the
> > 'simple multiplication' formulas and relationships. Learn the
> > "degrees C per watt" rating for a heatsink. Serious heatsink
> > manufacturers should provide a chart that related that "degree
> > C per watt" number to an LFM number - the speed that air moves
> > through that CPU.
>
> Ari doesn't move through a CPU, electricity does. Did you mean heatsink?

Best to clarify I suppose, but I think the answer is fairly obvious.
Anonymous
a b B Homebuilt system
a b à CPUs
September 8, 2004 8:23:29 PM

Archived from groups: alt.comp.hardware.pc-homebuilt,uk.comp.homebuilt (More info?)

Sentence should have read "CPU heatsink". My mistake
properly noted and therefore corrected here.

spodosaurus wrote:
> w_tom wrote:
>> Passive cooling is not difficult. But firsto learn the
>> 'simple multiplication' formulas and relationships. Learn the
>> "degrees C per watt" rating for a heatsink. Serious heatsink
>> manufacturers should provide a chart that related that "degree
>> C per watt" number to an LFM number - the speed that air moves
>> through that CPU.
>
> Ari doesn't move through a CPU, electricity does. Did you mean heatsink?
Anonymous
a b B Homebuilt system
a b à CPUs
September 8, 2004 11:21:37 PM

Archived from groups: alt.comp.hardware.pc-homebuilt (More info?)

John Fryatt wrote:

>>In your place I would mount together the PC using also bigger HS with
>>bigger & slower fans & run them on reduced voltage + a quality
>>designed case with a god probably (overrated) 2-fan PSU with regulated
>>fan RPMs & self thermocontroled too ...
>>
>>Full "ducting" in really not necessary; some hard cardBoard paper may
>>be useful to make some "flaps type" air directors to enhance fluid
>>airFlow thru the case & reducing fan speeds @ 2/3 (7V!) IMHO would be
>>enough for your setup!
>
>
>>IMHO with these days "powerfull" CPUs, I do not recommend trying
>>making a fanless air Cpu cooling at home; running minimum a bigger fan
>>@ 5V on its bigger HS is a better solution. (see the temps-my
>>experiment under Comp/benches ...)
>
>
> Thanks for the advice. I'll certainly look at your site.
>
> As I see it I am not proposing fanless cooling for the CPU, but rather a
> setup where the fan is not mounted directly on top of the heat sink. That
> way, as you say, it can be bigger and run slower. The duct is to connect the
> fan to the heat sink, in effect. Also, the remote fan will dump the warmed
> air outside the cas, rahter than just circulate it inside, and also double
> up as general ventialtion device for the whole PC.
>
> I think this whole issue is not that simple, and needs a bit of thinking
> about, including doing a few calculations, as w_tom suggested.
> Plan A is to get the PC built and running using the supplied heatsink fan
> from AMD. Plan B will then be to look at the ducting etc. as discussed here.
>
> Interestingly, my Dell started to acclerate it's fan a couple of times the
> other day, making me think about that.
> I'm tempted to see what I can do there to improve cooling. Initial thoughts
> are to...
> 1) lap the heatsink and put it back on with good thermal compund (e.g.
> 'Arctic Silver')

Assuming the fan's speed is adjusted by a thermal sensor at the fan's
intake, improving the CPU/heatsink thermal interface may improve the CPU
temperature a bit but it won't alter when the ducted fan accelerates
because the overall CPU watts is not altered. It would simply improve the
heatsink's transfer of heat to the air a bit, which would get hot, which
causes the fan to speed up.

> 2) make an extra vents in the front of the case (this is a Dell Dimension
> 8300, and the new 8400 has the same case design except for an additional
> vent in the front for "improved cooling" - admittedly for faster 3.4GHz
> CPUs)

Does the 8400 have exactly the same duct and fan?

The thing to keep in mind is that 'extra' vents will alter the internal
airflow. As an extreme, but illustrative, example imagine you remove the CD
drives and front panel covers on the top 5 1/4 inch drive bays so they
become a 'big vent'. Virtually all air pulled in by the rear fan will come
through that large upper 'vent' with very little induced through the bottom
intake, leaving little airflow across the lower half of the motherboard,
PCI slots, and hard drive area.


> Thanks for all your advice everyone, it's been illuminating.
>
> Regards, John
>
>
>
>
Anonymous
a b B Homebuilt system
a b à CPUs
September 9, 2004 8:30:42 AM

Archived from groups: alt.comp.hardware.pc-homebuilt,uk.comp.homebuilt (More info?)

John Fryatt wrote:
> "spodosaurus" <spodosaurus@_yahoo_.com> wrote in message
> news:413ea38c$1@quokka.wn.com.au...
>
>>w_tom wrote:
>>
>>> Passive cooling is not difficult. But firsto learn the
>>>'simple multiplication' formulas and relationships. Learn the
>>>"degrees C per watt" rating for a heatsink. Serious heatsink
>>>manufacturers should provide a chart that related that "degree
>>>C per watt" number to an LFM number - the speed that air moves
>>>through that CPU.
>>
>>Ari doesn't move through a CPU, electricity does. Did you mean heatsink?
>
>
> Best to clarify I suppose, but I think the answer is fairly obvious.
>
>

He could've merged two thoughts: air over the CPU (beneath the heatsink)
and air through the heatsink. While *I* know (99% sure) what he meant, a
newbie might get confused.

--
spammage trappage: replace fishies_ with yahoo
Anonymous
a b B Homebuilt system
a b à CPUs
September 9, 2004 9:34:04 PM

Archived from groups: alt.comp.hardware.pc-homebuilt,uk.comp.homebuilt (More info?)

w_tom wrote:
> Sentence should have read "CPU heatsink". My mistake
> properly noted and therefore corrected here.
>
> spodosaurus wrote:
>
>>w_tom wrote:
>>
>>> Passive cooling is not difficult. But firsto learn the
>>>'simple multiplication' formulas and relationships. Learn the
>>>"degrees C per watt" rating for a heatsink. Serious heatsink
>>>manufacturers should provide a chart that related that "degree
>>>C per watt" number to an LFM number - the speed that air moves
>>>through that CPU.
>>
>>Ari doesn't move through a CPU, electricity does. Did you mean heatsink?

^^^^^ ahaha I meant air...Ari is my first name hehe

--
spammage trappage: replace fishies_ with yahoo
Anonymous
a b B Homebuilt system
a b à CPUs
September 9, 2004 10:32:35 PM

Archived from groups: alt.comp.hardware.pc-homebuilt (More info?)

> > Interestingly, my Dell started to acclerate it's fan a couple of times
the
> > other day, making me think about that.
> > I'm tempted to see what I can do there to improve cooling. Initial
thoughts
> > are to...
> > 1) lap the heatsink and put it back on with good thermal compund (e.g.
> > 'Arctic Silver')
>
> Assuming the fan's speed is adjusted by a thermal sensor at the fan's
> intake, improving the CPU/heatsink thermal interface may improve the CPU
> temperature a bit but it won't alter when the ducted fan accelerates
> because the overall CPU watts is not altered. It would simply improve the
> heatsink's transfer of heat to the air a bit, which would get hot, which
> causes the fan to speed up.

Yes, I see your point. I'll have to find out where the sensor is. I was
assuming that the fan responded to the actual CPU's temperature, in which
case better heat trtansfer to the heatsink would delay acceleration of the
fan, yes? Assumptions are dangerous though - better to find out the facts.

> > 2) make an extra vents in the front of the case (this is a Dell
Dimension
> > 8300, and the new 8400 has the same case design except for an additional
> > vent in the front for "improved cooling" - admittedly for faster 3.4GHz
> > CPUs)
>
> Does the 8400 have exactly the same duct and fan?

I believe so, but I'd check before getting out the drill and saw. ;-)

> The thing to keep in mind is that 'extra' vents will alter the internal
> airflow. As an extreme, but illustrative, example imagine you remove the
CD
> drives and front panel covers on the top 5 1/4 inch drive bays so they
> become a 'big vent'. Virtually all air pulled in by the rear fan will come
> through that large upper 'vent' with very little induced through the
bottom
> intake, leaving little airflow across the lower half of the motherboard,
> PCI slots, and hard drive area.

Absolutely. I remeber having a discussion some time ago about cooling and
someone thought cooling would be better with the case lid completely off.
That's pretty much always *not* the case though as the airflow is totally
messed up with the lid.

If I did make extra vents I'd probably be thinking in terms of making the
extra intake air flow over the hard disk(s). By default I'll do nothing
though, and only wield the tools once I feel happy I a good idea of what's
happening.

John
Anonymous
a b B Homebuilt system
a b à CPUs
September 9, 2004 10:51:22 PM

Archived from groups: alt.comp.hardware.pc-homebuilt (More info?)

John Fryatt wrote:

>>>Interestingly, my Dell started to acclerate it's fan a couple of times
>
> the
>
>>>other day, making me think about that.
>>>I'm tempted to see what I can do there to improve cooling. Initial
>
> thoughts
>
>>>are to...
>>>1) lap the heatsink and put it back on with good thermal compund (e.g.
>>>'Arctic Silver')
>>
>>Assuming the fan's speed is adjusted by a thermal sensor at the fan's
>>intake, improving the CPU/heatsink thermal interface may improve the CPU
>>temperature a bit but it won't alter when the ducted fan accelerates
>>because the overall CPU watts is not altered. It would simply improve the
>>heatsink's transfer of heat to the air a bit, which would get hot, which
>>causes the fan to speed up.
>
>
> Yes, I see your point. I'll have to find out where the sensor is. I was
> assuming that the fan responded to the actual CPU's temperature, in which
> case better heat trtansfer to the heatsink would delay acceleration of the
> fan, yes?

One would think so.

> Assumptions are dangerous though - better to find out the facts.

You bet, which is why I made a point of what my assumption was. I guessing
as I've not dissected that model but self contained thermal control fans
are just so 'dime a dozen' cheap and easy. Slap it in: no 'special' BIOS,
wires to the heatsink, or anything else needed.


>>>2) make an extra vents in the front of the case (this is a Dell
>
> Dimension
>
>>>8300, and the new 8400 has the same case design except for an additional
>>>vent in the front for "improved cooling" - admittedly for faster 3.4GHz
>>>CPUs)
>>
>>Does the 8400 have exactly the same duct and fan?
>
>
> I believe so, but I'd check before getting out the drill and saw. ;-)
>
>
>>The thing to keep in mind is that 'extra' vents will alter the internal
>>airflow. As an extreme, but illustrative, example imagine you remove the
>
> CD
>
>>drives and front panel covers on the top 5 1/4 inch drive bays so they
>>become a 'big vent'. Virtually all air pulled in by the rear fan will come
>>through that large upper 'vent' with very little induced through the
>
> bottom
>
>>intake, leaving little airflow across the lower half of the motherboard,
>>PCI slots, and hard drive area.
>
>
> Absolutely. I remeber having a discussion some time ago about cooling and
> someone thought cooling would be better with the case lid completely off.
> That's pretty much always *not* the case though as the airflow is totally
> messed up with the lid.

Yeah. That's true if the case depends on specific airflow paths but not
necessarily so with the swiss cheese, vent holes all over the place, models.

>
> If I did make extra vents I'd probably be thinking in terms of making the
> extra intake air flow over the hard disk(s).

That makes good sense and you could always 'fine tune' it with tape if needed.

> By default I'll do nothing
> though, and only wield the tools once I feel happy I a good idea of what's
> happening.
>
> John
>
>
!