[s-cars] Thermal properties of anodizing Aluminum

[mlp qwest]

Thanks Mike, I did some more hunting on the net, & came across two pdf
publications from a company called R-Theta, apparently a major manufacturer
of heat sinks, among other products, for the electronics industry.  From one
of the r-theta pdf files,

 http://www.r-theta.com/products/extrusion/part1.pdf see beginning @ page 6,
I (& remember I obviously ain't no engineer, ... by a long shot) R-theta

For alloys &/or extrusions (not that I have much choice in this.  The IC's
are built, & I doubt any core mfg is going cater to any particular material
preference I might have as far as core material is concerned), R-Theta looks
at 6063 or 6061.

If given a choice, R-Theta apparently would prefer Aluminum 6063 to 6061.
6063 conducts 15% more heat than 6061; is easily more easily extruded and
worked; and "... Takes a finish very well providing consistent anodizing..."
The pdf file includes two table of heat transfer values, one for transfer
via "conductivity":

	  Thermal Conductives of Some relevant materials at 25 C
		Air (not moving)		  0.026
		Alumina			 31.-
		Aluminum 6061		171.-
		Aluminum 6063           193.-
		Anodize Coating  		  7.-
		.....
		Diamond               2,000.-
		Silver			417.-
		Steal, low Carbon		 46.-
		Stainless			 16.-
		Titanium             ? 8 to 20

2.  Further on in a table on "Emisivity" values on page 7, R-theta lists a
sample of comparative material "emisivity" or radiant heat transfer values
for several Material & Surface Finishes, including:
	  Material / Finish          Normal Emisivity
	Aluminum, polished		0.06
	Aluminum, oxidized		0.10 to 0.33
	Aluminum, chromated		0.10
	Aluminum, irridated		same
	Aluminum, anodized		0.70 to 0.90*

* Note a "maximum value, ? a perfect black body, on the "Emisivity" scale is
1.

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, 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.

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, but then again Ricers don't have any problem with
purple wiper blades or coffee can exhaust pipes, ... if it moves merchandize
either.  On the other hand, they also don't have either a radiator or hot
engine block "emitting" right behind there CPU's either.

Mike "Still Open to suggestions before they pull the big switch on the
Anodizing pond" Pederson
aka Mike "Warden, did the Governor Call?" Pederson

~-----Original Message-----
~From: Michael Bess [mailto:mlbess at optonline.net]
~
~FWIW, just remember that anodizing effectively turns the surface
~to aluminum
~oxide, a ceramic with lower intrinsic thermal conductivity in comparison to
~aluminum (which has a thermal conductivity on the order of 120-160
~BTU/hr/ft^2 depending upon alloy & temperature).  In bulk form I would
~estimate the thermal conductivity to be no more than 10% that of aluminum.
~However, at the thin coatings we are talking about (.1 to 1.0 mils) the
~effect would probably not be as large.  Without going into transport
~equations, and realizing that any interface creates a thermal barrier, the
~effect is there, but to what extent?  Also remember that aluminum will
~naturally oxidize and create a similar thermal barrier.
~
~
~Mike Bess
~'95 S6
~
~
~-----Original Message-----
~From: s-car-list-admin at audifans.com [mailto:s-car-list-admin at audifans.com]
~On Behalf Of mlp qwest
~Sent: Wednesday, February 12, 2003 1:11 PM
~To: s-car-list at audifans.com
~Subject: [s-cars] Thermal properties of anodizing Aluminum
~
~Anyone on the list have any particular knowledge or expertise on
~the thermal
~effects of anodizing aluminum?
~
~I gather there are at least three (3) major types or subcategories
~anodizing, sometimes described or referred to as:
~
~1.	Type 1 - "Chromic Acid" ~> usually leaves very thin deposit
~
~2.	Type 2 - "Sulfuric Acid" ~>  ditto
~
~3.	Type III aka "Hard Coating" ~> a much thicker process, which can be
~done
~in a way to add  very different characteristics to aluminum.  Type III
~anodizing can, and is used to significantly inhibit aluminums
~otherwise high
~thermal heat exchange capabilities, as for example in coating aluminum
~pistons to reject heat etc.
~
~Anyone know how processes 1 or 2 affect aluminums heat transfer
~capabilities?
~'
~I'd like to know what, if any kinds of anodizing are done to ENHANCE heat
~transfer either by conductivity, or for convection transfer purposes.
~
~Thanks
~Mikee "Wondering if there could be a Purple Anodized Radiator in some one's
~future" P.
~
~
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