[Amps] Anodizing aluminum, painting etc.

[K8MLM at aol.com]

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 at 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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