[s-cars] Thermal properties of anodizing Aluminum

[MLP]

At 27 to 30 psi of boost, on a 60 ~ 80F F ambient temperature day,
Depending on your turbo, I believe one can see IC inlet temps of 400 F+.

While I believe one can actually "spec" or target a thickness,
I believe typical Type II anodizing results in an aluminum oxide layer of
approximately 3 mils or less thick, i.e., from although
http://www.anodizing.org/reference_guide.html seems to indicate Type II can
go quite a bit thicker:

Mil Spec 8625 F
Type IA Conventional coatings produced from chromic acid bath  Thickness
0.5µ-7.6µ

Type IB Low voltage chromic acid anodizing (20 volts)
Used for 7xxx series alloys  Thickness  0.5µ-7.6µ

Type II Conventional coatings produced from
	Sulfuric acid bath ~  1.8µ-25.4µ

Type III Hard coat (Uniform anodic coatings)
       12.7µ-115µ

A Loctite reference says Type II coatings can be varied from @ 0.0001" to
0.001" (0.0025 to 0.025mm); others seem to imply the 0.0001 would be very
thin, and something more like .0005" would be a more likely minimum value.
I need to ask the local anodizer what thet plan on dialing in for as a
deposit goal (see, new reservation/question about amount of current required
vs. fin thickness, below.)

As for overall "dimensions" well, the "gross" IC core sizes vary, but the
basic overall dimensions are roughly
24" long x 10" high x 3" to (Hapersized) 4" thick.

I suspect however this isn't the "key" dimension you are asking for.  For
thermal transfer purposes, I'm guessing what you would want is something
approximating the overall convoluted surface area formed of hundreds, if not
thousands of tinny, tiny aluminum radiator fins, both EXTERNAL, AND, if one
wants to allow the anodizing solution to fill, and coat the inside of the
radiator or intercooler when the current is applied, INTERNALLY as well.

In any event, I appreciate your input Jonathan.  Hum, I see there is also
information about additional processes to "seal" the application as well,
and a warning about minimum material thicknesses vis-à-vis the amount of
electrical current that needs to be applied.  Hum, I think I'm going to see
if I can get the anodizer to run a small piece of left over scrap core as a
test.

mike

-----Original Message-----
From: J. Khang [mailto:jhlk99 at yahoo.com]

> Message: 12
> From: "mlp qwest" <mlped at qwest.net>

> I'm open to suggestion as to how one assess the
> merits of Anodizing, apparently some loss, no idea
> how much, of thermal conductivity as a result of
> covering the 6061 or 6063 core with a TEM value of
> 7, vs. the base materials natural value of 171 to
> 193

Easy, do the sums. It depends on the thickness of the
'lagging' and the dimensions of the object being
insulated. For thin tubes, you can actually cause an
increase in heat transfer but unlikely in this case.

>, against the "gain" in thermal emisvity of going
> from @ 0.10 to 0.33 (NE of naturally Oxidized
> Aluminum) a Natural Emisivity value of 0.70 to 0.9
> for Anodized Aluminum.

At what temperature? Sums easily performed again.

> Apparently, FWIW the computer heat sink makers don't
> seem to have a lot of worries about the adverse
> effects of anodizing on conductivity heat transfer
> values for CPU heat sinks

They wouldn't, the oxide layer is negligibly thin.

Jonathan
'96 S6