| Author |
Message |
Montie
Guest
|
 Posted:
Mon Nov 28, 2005 5:35 pm Post subject:
Painted Heat Sinks |
|
|
Morning,
Have you had any experience with painted heat sinks? I have a customer
who would like a painted finish and I'm having a hard time finding the
thermal conductivity of paint so I can calculate what the thermal
effect would be.
Any suggestions?
Thanks,
Montie
montie@montie.com
Montie Design
www.montie.com
|
|
| Back to top |
|
 |
John Larkin
Guest
|
| Posted:
Mon Nov 28, 2005 5:35 pm Post subject:
Re: Painted Heat Sinks |
|
|
On 28 Nov 2005 08:34:49 -0800, "Montie" <montie@montie.com> wrote:
| Quote: | Morning,
Have you had any experience with painted heat sinks? I have a customer
who would like a painted finish and I'm having a hard time finding the
thermal conductivity of paint so I can calculate what the thermal
effect would be.
|
It's huge compared to the thermal conductivity of still air, so it
won't change things much. The only interesting case would be with
high-velocity forced air flow, where it may be worth doing the math.
Why not anodize? That's probably easier than painting.
John |
|
| Back to top |
|
|
w_tom
Guest
|
| Posted:
Mon Nov 28, 2005 5:35 pm Post subject:
Re: Painted Heat Sinks |
|
|
With each change of medium is an increase in thermal
resistance. CPU to thermal compound to heatsink has higher
thermal resistance (conducts less heat) than CPU direct to
heatsink. Thermal resistance increased due to medium changes.
Yes, you can paint the heatsink. Probably matters little
the type of paint used. Medium is heatsink, through paint,
then to air (3 mediums) instead of heat direct to air (2
mediums). The third medium causes thermal resistance
increase. Then there is this thing called black body
radiators which also would be lost in painting.
Up front number is 'degrees C per watt' which includes
thermal resistance of those medium changes. That number is
what heatsink manufacturers (the responsible ones) and you
both worry about. Painting will only adversely increase that
number.
Would not worry about paint's thermal conductivity number.
A medium change will increase thermal resistance anyway.
Montie wrote:
| Quote: | Have you had any experience with painted heat sinks? I have a customer
who would like a painted finish and I'm having a hard time finding the
thermal conductivity of paint so I can calculate what the thermal
effect would be. |
|
|
| Back to top |
|
|
Ignoramus4324
Guest
|
| Posted:
Mon Nov 28, 2005 11:38 pm Post subject:
Re: Painted Heat Sinks |
|
|
I suspect that using black paint can actually improve heat
dissipation, due to increased radiation of heat as opposed to a shiny
reflective surface.
i
On Mon, 28 Nov 2005 12:32:37 -0500, w_tom <w_tom1@hotmail.com> wrote:
| Quote: | With each change of medium is an increase in thermal
resistance. CPU to thermal compound to heatsink has higher
thermal resistance (conducts less heat) than CPU direct to
heatsink. Thermal resistance increased due to medium changes.
Yes, you can paint the heatsink. Probably matters little
the type of paint used. Medium is heatsink, through paint,
then to air (3 mediums) instead of heat direct to air (2
mediums). The third medium causes thermal resistance
increase. Then there is this thing called black body
radiators which also would be lost in painting.
Up front number is 'degrees C per watt' which includes
thermal resistance of those medium changes. That number is
what heatsink manufacturers (the responsible ones) and you
both worry about. Painting will only adversely increase that
number.
Would not worry about paint's thermal conductivity number.
A medium change will increase thermal resistance anyway.
Montie wrote:
Have you had any experience with painted heat sinks? I have a customer
who would like a painted finish and I'm having a hard time finding the
thermal conductivity of paint so I can calculate what the thermal
effect would be.
|
-- |
|
| Back to top |
|
|
GregS
Guest
|
| Posted:
Mon Nov 28, 2005 11:44 pm Post subject:
Re: Painted Heat Sinks |
|
|
In article <k3emo150mtk5jssclindf2p5k1sv5cc7t7@4ax.com>, John Larkin <jjlarkin@highNOTlandTHIStechnologyPART.com> wrote:
| Quote: | On 28 Nov 2005 08:34:49 -0800, "Montie" <montie@montie.com> wrote:
Morning,
Have you had any experience with painted heat sinks? I have a customer
who would like a painted finish and I'm having a hard time finding the
thermal conductivity of paint so I can calculate what the thermal
effect would be.
It's huge compared to the thermal conductivity of still air, so it
won't change things much. The only interesting case would be with
high-velocity forced air flow, where it may be worth doing the math.
Why not anodize? That's probably easier than painting.
John
|
Powder coat is probably thicker than standard paint, which may hinder things.
greg |
|
| Back to top |
|
|
John Larkin
Guest
|
| Posted:
Tue Nov 29, 2005 1:18 am Post subject:
Re: Painted Heat Sinks |
|
|
On Mon, 28 Nov 2005 17:38:49 GMT, Ignoramus4324
<ignoramus4324@NOSPAM.4324.invalid> wrote:
| Quote: | I suspect that using black paint can actually improve heat
dissipation, due to increased radiation of heat as opposed to a shiny
reflective surface.
|
Radiation effect is tiny at the temperatures seen on ordinary heat
sinks. The paint's thermal resistance will likely make things worse
than any increase in radiation.
John |
|
| Back to top |
|
|
Spehro Pefhany
Guest
|
| Posted:
Tue Nov 29, 2005 1:36 am Post subject:
Re: Painted Heat Sinks |
|
|
On Mon, 28 Nov 2005 11:18:56 -0800, the renowned John Larkin
<jjlarkin@highNOTlandTHIStechnologyPART.com> wrote:
| Quote: | On Mon, 28 Nov 2005 17:38:49 GMT, Ignoramus4324
ignoramus4324@NOSPAM.4324.invalid> wrote:
I suspect that using black paint can actually improve heat
dissipation, due to increased radiation of heat as opposed to a shiny
reflective surface.
Radiation effect is tiny at the temperatures seen on ordinary heat
sinks. The paint's thermal resistance will likely make things worse
than any increase in radiation.
John
|
Radiation works both ways, though, and if you've got hot stuff nearby
(such as those thermionic devices or some kind of space-based
thermonuclear reactor) you could get the HS 'seeing' the hot stuff
rather than reflecting the IR off. So maybe they should be black on
the cold side and shiny on side that sees the sun or whatever.
Best regards,
Spehro Pefhany
--
"it's the network..." "The Journey is the reward"
speff@interlog.com Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog Info for designers: http://www.speff.com |
|
| Back to top |
|
|
Dave
Guest
|
|
| Back to top |
|
|
John Larkin
Guest
|
| Posted:
Tue Nov 29, 2005 1:36 am Post subject:
Re: Painted Heat Sinks |
|
|
On Mon, 28 Nov 2005 22:27:04 GMT, Gandalf
<Spam_Bin@ourwonderful.sytes.net> wrote:
| Quote: | On 28 Nov 2005 08:34:49 -0800, "Montie" <montie@montie.com> wrote:
Morning,
Have you had any experience with painted heat sinks? I have a customer
who would like a painted finish and I'm having a hard time finding the
thermal conductivity of paint so I can calculate what the thermal
effect would be.
Any suggestions?
Thanks,
Montie
montie@montie.com
Montie Design
www.montie.com
If you're using convective cooling and have cool surroundings to radiate to,
glossy black oil based enamel will considerably boost the cooling over bare
aluminum. Anodizing doesn't seem to do anything for the long wavelength infrared
radiation needed for the lower heatsink surface temps.
On one project, I needed .35C/W cooling but the best aluminum extrusion I could
buy would only give .5C/watt. By painting with black oil enamel, I got my
.35C/W.
If you're using forced air on a relatively cool (less than 100C) aluminum
heatsink, anodizing would be the simplest way to get color without affecting
performance.
|
According to the little prog I have, a heatsink of 100 sq cm area, 50
C above ambient, emissivity = 1.0, radiates a tad under 4 watts.
That's about 12.5 c/watt, and a 50C rise is pretty radical in most
apps. For a 30C rise, more reasonable maybe, it's more like 2 watts.
If it's inside a non-black box, some of its radiation will be
reflected back. Similarly, parallel fins mostly just radiate at each
other, which can defeat most of the radiative cooling effect.
John |
|
| Back to top |
|
|
Keith Williams
Guest
|
| Posted:
Tue Nov 29, 2005 1:36 am Post subject:
Re: Painted Heat Sinks |
|
|
In article <ikqmo1tmj0fd7t931hg8q0eloftkju7bsl@4ax.com>,
speffSNIP@interlogDOTyou.knowwhat says...
| Quote: | On Mon, 28 Nov 2005 11:18:56 -0800, the renowned John Larkin
jjlarkin@highNOTlandTHIStechnologyPART.com> wrote:
On Mon, 28 Nov 2005 17:38:49 GMT, Ignoramus4324
ignoramus4324@NOSPAM.4324.invalid> wrote:
I suspect that using black paint can actually improve heat
dissipation, due to increased radiation of heat as opposed to a shiny
reflective surface.
Radiation effect is tiny at the temperatures seen on ordinary heat
sinks. The paint's thermal resistance will likely make things worse
than any increase in radiation.
John
Radiation works both ways, though, and if you've got hot stuff nearby
(such as those thermionic devices or some kind of space-based
thermonuclear reactor) you could get the HS 'seeing' the hot stuff
rather than reflecting the IR off. So maybe they should be black on
the cold side and shiny on side that sees the sun or whatever.
|
The "color" in visible light is irrelevant, unless the HS is
radiating in the visible spectrum. I suggest this is usually
badness in this bidness. ;-)
--
Keith |
|
| Back to top |
|
|
Spehro Pefhany
Guest
|
| Posted:
Tue Nov 29, 2005 1:36 am Post subject:
Re: Painted Heat Sinks |
|
|
On Mon, 28 Nov 2005 15:46:03 -0500, the renowned Keith Williams
<krw@att.bizzzz> wrote:
| Quote: | In article <ikqmo1tmj0fd7t931hg8q0eloftkju7bsl@4ax.com>,
speffSNIP@interlogDOTyou.knowwhat says...
On Mon, 28 Nov 2005 11:18:56 -0800, the renowned John Larkin
jjlarkin@highNOTlandTHIStechnologyPART.com> wrote:
On Mon, 28 Nov 2005 17:38:49 GMT, Ignoramus4324
ignoramus4324@NOSPAM.4324.invalid> wrote:
I suspect that using black paint can actually improve heat
dissipation, due to increased radiation of heat as opposed to a shiny
reflective surface.
Radiation effect is tiny at the temperatures seen on ordinary heat
sinks. The paint's thermal resistance will likely make things worse
than any increase in radiation.
John
Radiation works both ways, though, and if you've got hot stuff nearby
(such as those thermionic devices or some kind of space-based
thermonuclear reactor) you could get the HS 'seeing' the hot stuff
rather than reflecting the IR off. So maybe they should be black on
the cold side and shiny on side that sees the sun or whatever.
The "color" in visible light is irrelevant, unless the HS is
radiating in the visible spectrum. I suggest this is usually
badness in this bidness. ;-)
|
Black and shiny are not colors.
Best regards,
Spehro Pefhany
--
"it's the network..." "The Journey is the reward"
speff@interlog.com Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog Info for designers: http://www.speff.com |
|
| Back to top |
|
|
John Larkin
Guest
|
| Posted:
Tue Nov 29, 2005 1:36 am Post subject:
Re: Painted Heat Sinks |
|
|
On Mon, 28 Nov 2005 20:31:01 GMT, "Dave" <dave@nospam.com> wrote:
His example 2 is just silly. If you glop on tons of silicone grease
and apply even modest mounting pressure, it oozes down to under 100
microinches.
John |
|
| Back to top |
|
|
w_tom
Guest
|
| Posted:
Tue Nov 29, 2005 1:36 am Post subject:
Re: Painted Heat Sinks |
|
|
John's post adds details to this previously posted sentence:
| Quote: | Then there is this thing called black body radiators
which also would be lost in painting.
|
Heat sinks are colored dull black so that the minor
additional cooling from radiation will decrease the important
number - 'degrees C per watt'. But as John notes, the
additional cooling by radiation is minor.
John Larkin wrote:
| Quote: | Radiation effect is tiny at the temperatures seen on ordinary heat
sinks. The paint's thermal resistance will likely make things worse
than any increase in radiation. |
|
|
| Back to top |
|
|
Gandalf
Guest
|
| Posted:
Tue Nov 29, 2005 1:36 am Post subject:
Re: Painted Heat Sinks |
|
|
On 28 Nov 2005 08:34:49 -0800, "Montie" <montie@montie.com> wrote:
| Quote: | Morning,
Have you had any experience with painted heat sinks? I have a customer
who would like a painted finish and I'm having a hard time finding the
thermal conductivity of paint so I can calculate what the thermal
effect would be.
Any suggestions?
Thanks,
Montie
montie@montie.com
Montie Design
www.montie.com
|
If you're using convective cooling and have cool surroundings to radiate to,
glossy black oil based enamel will considerably boost the cooling over bare
aluminum. Anodizing doesn't seem to do anything for the long wavelength infrared
radiation needed for the lower heatsink surface temps.
On one project, I needed .35C/W cooling but the best aluminum extrusion I could
buy would only give .5C/watt. By painting with black oil enamel, I got my
..35C/W.
If you're using forced air on a relatively cool (less than 100C) aluminum
heatsink, anodizing would be the simplest way to get color without affecting
performance. |
|
| Back to top |
|
|
Adrian Tuddenham
Guest
|
| Posted:
Tue Nov 29, 2005 5:35 pm Post subject:
Re: Painted Heat Sinks |
|
|
w_tom <w_tom1@hotmail.com> wrote:
| Quote: | John's post adds details to this previously posted sentence:
Then there is this thing called black body radiators
which also would be lost in painting.
Heat sinks are colored dull black so that the minor
additional cooling from radiation will decrease the important
number - 'degrees C per watt'. But as John notes, the
additional cooling by radiation is minor.
|
That may be good for the written specification, but it is not what you
want for outdoor P.A. gear which may be used in strong sunshine; it will
absorb more radiant energy because of it.
I'm not sure that all polished metals reflect infra-red wavelengths
well, either. I have recollections of 'reflective' car tools getting
very hot when left lying around in the sunshine.
--
~ Adrian Tuddenham ~
(Remove the ".invalid"s and add ".co.uk" to reply)
www.poppyrecords.co.uk |
|
| Back to top |
|
|
|
|
|
|
FAQ
Memberlist
Register
Profile
Log in to check your private messages
Log in