There are 3 modes of heat transfer;
-radiation,
-conduction and
-convection ... where a moving fluid (air) carries the heat away.
The convection mode of heat transfer comes into play for the heatsink to get
rid of heat to the air by conducting the heat to the air.
A black anodized heatsink will radiate more heat than a silver one will as
long as it is not "in view" of another radiant heat source... like next to the
glowing red anode of a big glass tube.
Regarding conduction (transfer from the heat source to the heatsink and from
the heatsink to the air), the Back Anodizing won't make much difference.
The insulating quality (elimination heat transfer by conduction) of Back
Anodizing is for all practical purposes, nil.
Regarding convection; it won't make any difference. The thing of most
importance is air or fluid flow.... so keep the heatsink clean and free of
dust.
I actually like Red or Blue Anodizing on my heatsinks. My XYL likes pink.
Bob
K8MLM
In a message dated 8/16/2006 12:38:56 A.M. Eastern Daylight Time,
craxd1@verizon.net writes:
Peter,
I agree on the math. The problem I see on using a black heatsink is that
even
though all heat is infrared, and there's a concentrated heat transfer from
the device
to the heatsink, using black supposedly helps this transfer. The problem
arises in
the day time, or around any source of infrared radiation in that the
heatsink would
absorb this radiation becoming hotter than would a silver surface which
would reflect
it off of it. The heatsink though would still radiate it's heat if silver.
To my opinion,
using a good thermal heatsink compound with a silver heatsink works probably
better
or just as good. If black works like they say for the device, why not make a
black
silicone grease for the thermal compound? Most I've seen is gray or white!
That then
is in between the black heatsink, or an insulator is used which Is generally
not black
either. On top of that, to my opinion the anodizing creates a surface
insulation the
same way it does on the foil of an electrolytic capacitor. I just don't
think anodizing a
heatsink is as good as some make it out to be when you start picking it
apart and
investagating it with reason. The best place to run a black heatsink would
be in the
dark away from any infrared sources that it could absorb heat from. I place
more faith
in the mass of the heatsink and the way the fins are designed rather than
its color.
That's just my opinion on it.
Best,
Will
*********** REPLY SEPARATOR ***********
On 8/15/06 at 8:21 AM Peter Chadwick wrote:
>If you had a heat sink of zero mass, infinite conductivity and zero
>thermal resistance btween sink and air, it would work perfectly, no matter
>what size it was. So mass itself doesn't matter: the implication is that
>greater mass equates to greater area and lower thermal resistance. After
>all, which is going to give best results - 500 grams (OK, 1 pound in the
>US!) of depleted uranium or 500 grams (1 pound) of aluminium? The
>aluminium obviously has a greater volume, and thus a greater surface area.
>In this imperfect world, the mass times the specific heat tells you how
>many calories are needed to raise the sink temperature above ambient by
>some amount. The power being dissipated at 4.2 Joules/calorie tells you
>how long it takes to do it. The Theta sink-to-air tells you how much heat
>the sink is losing. The complication then occurs because the sink is not
>generally at equal temperature all over. In any case, all you're really
>interested in at the end of the day is Theta-junction-to-ambient. From
>memory, you can end up with set of simultaneous second order differential
>equations trying to work it all out from first principles, and those are
>things that I avoid!
>
>73
>Peter G3RZP
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>Amps@contesting.com
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