Paul,
The black color only has to do with infrared radiation, the same as white, and
nothing to do with the heat transfer from the device to the heatsink. The black
absorbs this radiation and white reflects it. Anodizing is an electro-chemical
coating which uses a die for the color. The surface is etched, then dipped in
the electro-chemical bath containing the die which is a similar process to
plating. This forms a skin on the aluminum about 1 mil or so thick similar to
the way they make the anode foil in an electrolytic capacitor. That forms an
insulator which combined with the electrolyte acts similar to a diode in
function (unless it's a non-polarized type of cap). The term insulator is the
key word here (electrical or heat) where I think it can actually impede the
thermal transfer between the device and heatsink by some amount. I would rather
have that junction be bare aluminum, but the rest could be colored. Most
heatsinks though used to mount power RF devices have a series of
tall fins which really should be fan cooled where they're spaced close
together. Ones for other power devices (regulators, pass transistors, etc) are
made to dissapate heat into the air by the fin design.
Best,
Will
*********** REPLY SEPARATOR ***********
On 7/22/06 at 4:28 PM Paul Christensen wrote:
>> It could be that they think the same as I do. Any time you anodize
>> aluminum, there is actually a coating formed 1-2 mils deep on the
>> aluminum.
>
>Anodizing aluminum increases themicity and results in a substantially
>better
>heat radiator over that of bare aluminum. The vast majority of heat-sinks
>are anodized, usually black or gold. The anodizing process is a job best
>left for the experts. There should be someone in your area that
>specializes in the procedure.
>
>Paul, W9AC
>
>_______________________________________________
>Amps mailing list
>Amps@contesting.com
>http://lists.contesting.com/mailman/listinfo/amps
_______________________________________________
Amps mailing list
Amps@contesting.com
http://lists.contesting.com/mailman/listinfo/amps
|