[s-cars] FW: Anodizing effects on Aluminum thermal heat dissipation Q

[mlp qwest]

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RE: Anodizing effects on Aluminum thermal heat dissipation QFWIW, & for
those who care, I pass on the list following reply from the
aluminum.org/anodizing Guru, i.e Mr Nalewik:

Mike "now newly anodized fat & black, following in Brian B's footsteps" in
Colorado

-----Original Message-----
From: mlp qwest
Sent: Thursday, February 27, 2003 8:34 AM
To: JIM NALEWICK
Subject: RE: Anodizing effects on Aluminum thermal heat dissipation Q


Jim -

Thank you very much for your detailed & thoughtful reply.  In a separate
email I have forwarded to you, I've detailed the results, and my limited
ability to make sense of them, that some further searching on the internet
produced back on the 13th of February on the matter.  FWIW, my current
understanding of the matter is I'm looking at two major heat transfer modes,
convective & emissive.

The very general Rule of Thumb I came up with was that anodizing generally
greatly improves emissive heat transfer of aluminum, and (??) can slightly
impair convective transfer properties (see the quoted rtheta table of values
in the accompanying  February 13th email,)

I've made the leap of faith that the "conductive values" quoted by
R-theta.com of between 171 to 193 for "raw" 6061/6063 aluminum vs. @ 7 for
anodized is more or less worth the (a) gain in emissive values and (b) some
additional surface protection and (c) cosmetic values in the very thin
coating we would be looking at applying.  That in any event, given the
limited thickness of the anodized surface, and that an exposed raw aluminum
surface will, over time, developed a "natural" aluminum oxide surface in any
event, anodizing the convective surface would not (hopefully) have any
significant adverse effect.

Again,
Thanks
Mike Pederson
  -----Original Message-----
  From: JIM NALEWICK
  Sent: Thursday, February 27, 2003 7:52 AM
  To: 'mlped'
  Subject: RE: Anodizing effects on Aluminum thermal heat dissipation Q


  Mike,
  I am sorry that I have taken so long to answer your questions.  When I
came back from my trip, I had a project I was working on take up my time.

  Anodizing air intercoolers should help with the heat transfer.

  When looking as how heat is transfered from materials, you look at it's
Heat Emissivity.

  The book "The Surface Treatment And Finishing Of Aluminum And Its Alloys"
by S. Wernick, R. Pinner, and P.G. Sheasby, Fifth Edition published by ASM
International and Finishing Publications LTD. lists the following
information.

  Radiation numbers of aluminum

  Condition of            Radiation number                        Heat
emissivity
  Aluminum                [K cal/m^2 x h (deg K)^4]       %
  Mirror polished 0.2-0.3                         4.3-4.6
  Etched          0.3-0.4                         6.4-8.5
  Bright Rolled   0.25-0.35                               5.3-7.4
  Matt Rolled             0.4-0.75                                8.5-16
  Aluminum Painted        0.8-1.5                         17-32
  As diecast              0.75-1.2                                16-26
  As sandcast             1.2-1.7                         26-36
  Anodized                1.8-4.3                         38-92
  Black Body              4.70                                    100

  Data given lists that this is a function of film thickness.  Thicker films
radiate heat better then thinner films.
  1 um film (0.039 mils or 0.000039")  30% Heat emissivity
  2 um film (0.078 mils or 0.000078")  60% Heat emissivity
  3 um film (0.118 mils or 0.000118")  70% Heat emissivity

  I think the following quote says it all.  "It should be noted that
anodized aluminum is an excellent radiating surface which approaches to
within 80% of a 'black boy' regardless of its optical colour and there is no
advantage to be derived from dyeing it black."

  I have talked to some of our customers that used anodized aluminum for
heat sinks for chips.  They have found that when they use raw aluminum parts
of the same size the chips over heat and fail.  When they use anodized
parts, the chips stay cooler.

  I have other comments.
  1)  The high temperature of 400 F should be OK for anodized aluminum.  I
would expect that you would see thermal crazing of the parts when they get
hot.  The anodic coating will hold up to very high temperatures.  What
happens is that when the parts are heated, it will expand.  The aluminum
expands at a greater rate than the anodic coating (aluminum oxide).  The
aluminum oxide is a hard crystaline layer on the surface and when the
aluminum expands, cracks or craze lines will form in the coating.  The
coating will still stay attached to the aluminum and should not flake off.

  2) The anodic coating should hold up well to neutral salt spary.  Anodized
parts have been used in exterior automotive parts for years.  A standard
film thickness for automotive parts is 0.3 mils.  Thicker coatings will hold
up even better.  There can be problems if the parts are cleaned with caustic
or acid solutions.  I have seen were solutions used to wash trucks have high
enough pH to remove oils that they will dissolve the anodic coating.

  3)  Coloring the parts black will not change the thermal properties, but
may give you a good look.  You will need to look at how the parts a colored.

  There are two main was to color anodized aluminum black.

  First you can use an organic dye.  There are a number of different
companies that make black dye for use with anodized aluminum.  Each company
make 3 or 4 different black dyes.  Some dyes will hold up well to exposure
to UV light and high heat.  Other dyes will fade quickly when exposed to UV
light or high heat.

  A second method is to use a process called electrolytic two-step.  In this
process either tin or cobalt metal is plated in the pores of the anodic
coating before it is sealed.  These colors do not fade when the parts are
heated or exposed to UV light.  (We sell aluminum anodized with this process
for use in heating plates for Mr Coffee makers.)

  It will be much better than a painted product.



  If you have any more questions, please free to Email me.

  Jim Nalewick


  -----Original Mess-ge-----
  From: mlp qwest
  Sent: Wednesday, February 12, 2003 10:03 AM
  To: jimnalewick
  Subject: Anodizing effects on Aluminum thermal heat dissipation Q



  I am building aluminum air to air intercoolers (IC) for use in an
automotive
  application.  The ICs are used to cool the hot, compressed, incoming
intake
  charge in a turbocharged automotive application.  Operating temperature
can
  run as high as close to 400 F.

  The IC looks, works and is constructed similar to a car radiator (lots of
  thin internal & external aluminum fins.)  The hot, intake air under
pressure
  is run through the IC core.  Heat in the compressed air is supposed to
  transfer "conductively" to the walls of the IC, and then from there, then
  dissipated into the atmosphere, again principally via thermal conduction
  through the IC's external cooling fins.

  The ICs can be left bare, and installed as is.  But I would like to
consider
  anodizing, painting or otherwise coating the ICs at least externally, and
  possibly internally (anodizing my be the only alternative for coating
  internally) to:

  (1) Provide protection from external environmental factors (e.g. road
salts,
  grime etc.) &

  (2) Possibly protect or improve the internal transmsivity of the cores
  internal fins, if that's possible.  Internally, cores can be exposed to
some
  contamination from oil blow at turbocharger bearings;

  (3) Externally, if anodized or painted black, to provide some visual
  cosmetic concealment.

  I'm concerned about adversely affecting the IC's ability to transfer heat.

  Can someone tell me if anodizing aluminum reduces its ability to absorb
then
  transfer heat?  I believe this pertains more to "thermal conductivity"
than
  emissivity.

  Should the loss (or gain) in conductivity &/or emissivity from anodizing
be
  regarded as significant where the goal is to remove heat?  Is there a
  particular anodizing recommendation for this kind (i.e. IC) application?

  My current (obviously limited) understanding is in some cases anodizing
can
  be done to thermally insulate aluminum?  Is this the usual case, or does
  anodizing usually enhance thermal conductivity as I take the above
response
  suggests?  What would be the recommendation for anodizing something that
  works like a cars radiator (i.e. thermal conductivity enhancement)?

  Thanks in advance for any information you can shed on this

  Mike Pederson
  Denver, Colorado
  303-
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