aluminum heatsink anodizing

[Phil Allison]

"Adrian Tuddenham"

A point not often appreciated is the possible heat gain when a heatsink
is operated in bright sunshine. A surface finish which is a poor
radiator/absorber of radiant heat will work better in those
circumstances.

** Only a complete dope would not find some way to shade the heatsink from
direct sunlight on a hot day.




...... Phil

 

[IanM]

"Adrian Tuddenham"


** Only a complete dope would not find some way to shade the heatsink from
direct sunlight on a hot day.
..... Phil

I think you've just defined a 'roadie'
The only question is what's he doped on?

 

[neon]

alodizing anodizing is for the protection of the metal itself. from corrosionand such.buy thermal heatsink compounds to get a good bound.

 

[John Devereux]

"NoSPAM"
"Eeyore"

** You seem to have seriously MISREAD what he said.




** That is EXACTLY what his post says.

" If the heatsink is fan blown, then the main heat transfer mechanism is
conduction ...."

This refers to the heat energy being conducted into the forced air stream
and removed.




** Terminology often varies from one area of technology to another, one
place to another plus it varies over time as well.

In the world of *audio power amplifiers*, ones that have no fans are called
" convection cooled " while those that have installed fans are often called
" force air cooled " or just " fan cooled ".

If a number of amplifiers * without fans* are fitted into a cabinet (
called a " rack ") then normally several fans are fitted to the lower part
of that rack and force air up and through the amplifiers and out the top .

This is sometimes called " forced convection cooling " or more simply " a
fan cooled rack" .

Blowing an air stream over a hot surface might be called " assisted
convection " in some quarters - but that is no more "correct" than
saying the fast flowing air conducts the heat away.

Wow, it's coming to something when we have to rely on *Phil* to
provide the calm rationality around here

I agree FWIW, it's obviously just a difference in terminology usage.

 

[Rich Grise]

You're talking SHIT ! You're out of your depth. Where insulation is
required, the high tech polymer pads outperform EVERYTHING.

Ooh! A Holy War, that's actually about electronics! ;-)

I've never trusted sil-pads (or any other form of greaseless pad) since
day one.

I'm so enamoured of Dow Corning 340 grease that when I buy a new CPU
and heatsink kit, I clean off the goo that comes with the kit and
use my own personal (lifted from the USAF) DC-340.

Cheers!
Rich

 

[Rich Grise]

Who said mine need any machining ?

If it's extruded, it needs to be machined, especially if you're intending
to use the hard anodize as the insulator.

It's a rubbish way to get a flat
surface.

So you just fill in the imperfections with your crappy pads?

Put on your asbestos underpants and tell that to sci.engr.mech.

Cheers!
Rich

 

[Rich Grise]

No simple answer.

Sure there is!

The thermal resistance of sil-pads is so crappy, the treatment of the
heatsink itself won't make much difference.

If the device makes _good_ thermal contact, then anodized/painted is
better. Plain aluminum has very poor emissivity.

Cheers!
Rich

 

[Rich Grise]

... Obviously Eeyone has never blown air
across a spoonful of hot soup to cool it faster than just letting the
spoon sit in still air!

Not applicable - that's primarily evaporation.

Cheers!
Rich

 

[Eeyore]

If it's extruded, it needs to be machined, especially if you're intending
to use the hard anodize as the insulator.

Who said anything about extrusions ?

Graham

 

[Eeyore]

Not hard anodize. Especially not AlN. Most especially not BeO.

Just when I start to think that maybe you're not an absolute jerk, you
remind me that you are.

Unlike you, I don't have military budgets. My statement is correct for commercial
applications where money counts.

Graham

 

[Eeyore]

Ooh! A Holy War, that's actually about electronics! ;-)

I've never trusted sil-pads (or any other form of greaseless pad) since
day one.

The grey ones ? They're shit. Look elsewhere like AN1040 (link already
given).
http://www.bergquistcompany.com/objects/Thermal_Materials/Sil_Pad/Sil_Pad_Tables/SPComparison2.pdf

With a range of thermal conductivity from 0.9 to 3.5 you can't lump them
all together. And they conform to surfaces brilliantly.

Graham

 

[Eeyore]

You're an idiot. My last large sink product was a 1500W supply for a
CAT scanner for Philips. We used a custom extrusion

Totally unneccessary. And heavy.

Graham

 

[Eeyore]

No insulators at all of course... the heatsink is hot to the load.

Isn't that just what I recommended ?

This is in a 17KW peak-output MRI gradient driver.

And the dissipation in the devices is ?

Graham

 

[Eeyore]

Those are the same type of spring clip hold downs that we used.

I quite like those too but I prefer TO-3. You can run them hotter.

Graham

 

[Eeyore]

No you don't. A fan blowing air across a heatsink provides for greater
heat transfer from the sink to the aiir than does the natural convection
moving the heated air away slowly. Obviously Eeyone has never blown air
across a spoonful of hot soup to cool it faster than just letting the spoon
sit in still air!

Who said anything about blowing ACROSS a heatsink ? That's about the dumbest
thing to do.

Graham

 

[Eeyore]

No you don't.

The 2 kW version of this ran happily with the metal can output devices @ around
100C with
2 x 80mm fans blowing front to back.

http://cgi.ebay.co.uk/Studiomaster-...ryZ14973QQssPageNameZWDVWQQrdZ1QQcmdZViewItem

The one in the pic only needed 1 x 80mm fan (free air rated at 40CFM) and their
reliability is legendary. My local venue has a couple of them, both about 10
years old in daily use and all we've had to do is blow some dust out and
replace a slightly crackly 'volume pot'.

Graham

 

[Eeyore]

Not applicable - that's primarily evaporation.

Very true.

Graham

 

[Eeyore]

The terminology I'm used to here is "forced convection", which is a
transport mechanism. Conduction refers to heat transfer through
materials, like those crappy sil-pads.

So you're saying metal doesn't conduct heat to air are you ?

Better go back to your physics books John.

Graham

 

[Eeyore]

Wow, it's coming to something when we have to rely on *Phil* to
provide the calm rationality around here

I agree FWIW, it's obviously just a difference in terminology usage.

Since when does conduction = convection ? There's an easy proof it's conduction
btw but I don't plan to publicly give away my heatsink designs.

Graham

 

[Eeyore]

"Adrian Tuddenham"

** Only a complete dope would not find some way to shade the heatsink from
direct sunlight on a hot day.

There's no shortage of dopes.

Graham