To Anodize or Not...

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Hi Everyone,

After a long delay and many interim projects, its time to finish building my set of 100w Aleph-X amps for my basement theater (I am building 5 monoblocks). I have everything I need now except for the heat sinks. I have chosen to use this sink from MM Metals:http://www.mmmetals.com/extrusions/drawings/MM11645.JPG

Each monoblock will produce 100w and will need to dissipate 300w. The MM11645 is rated to 0.8c/w per 3" length, so I am planning on using four 10" lengths per chassis to achieve approx 0.06c/w per completed chassis.

So my question is this: should I have the extrusions black anodized or should I leave them a raw aluminum? How much radiative capacity do I lose if I leave then raw? I'm wondering if the cost of anodizing them is worth it...

Thanks,
Eric
 
dunno if the "black body" is worth that much % wise, check some heatsink mfrs sites to see what they say about it.

IF you get it anodized you want to make sure that it is "nickel sealed" or an equivalent process - tell the anodizer that it is going to get hot[/i]. Most straight dyes used in anodizing will turn color(s) over time - black notoriously turns purple.

Also you have to use the mfr's engineering data to derate heatsinks WRT length when used with natural convection.

FYI

_-_-bear
 
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I have both types of Heat sinks... the same M&M profile used on Aleph 2's.

I had to "arrange" the heat sinks to hide anodizing flaws but it worked out.
The cut edges are RAZOR sharp.

The power coating on the Conrad's that I also have for an Aleph J project look nicer,
and the corners are rounded a bit so I won't cut myself like I did while constructing,
and moving around the Aleph 2's.

Unfortunately Conrad doesn't make a tall profile and depending on how your output
devices are mounted, you may not be able to use two horizontally stacked pieces,
and I'm not sure that is the best way to use heat sinks.

I'm pretty sure the Conrads are cast and not extruded,
the back plate is thicker than the M&M sink. (2 to 3 mm's)
1004_c.JPG


I used 2 sections of M&M per side 9" tall on the Aleph 2's.
 

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5 channels of class A

Eric,
I built an Aleph 4, and am in the process of building 2 Aleph 30's to run the 2 front speakers in my stereo/surround system. Let me warn you about the heat generated by one Aleph 4. I use a fan in the room next door, and route the air under the amp which lives in a purpose built wooden rack. The blower is a 220 volt running on 110 to slow it down and make it quieter. The heat from the one amp eventually warms my 16 x 19 foot basement. I figure with the additional 2 Aleph 30's, I will have to close off the furnace grates that feed the room when I have the amps on. With 5 amps, you will have to actively manage the heat or it will run you out of the room. I am near Chicago so I get 7 months of cold weather and the basement is always cool, until I turn on the Aleph!
Good luck
Don
 
Nope, they specifically say it's "powder coated". In other words, covered in paint!

Black anodizing should result in about a 15 - 20% more efficient heatsink than plain aluminium :)

I don't think so. Check out this link.

Emissivity Coefficients of some common Materials

Black paint has a greater emissivity than anodized Al. Sprayed Al does also.

Another factor to consider is where the radiated energy goes. The fins of the heat sink are parallel and closely spaced.
 
I don't think so. Check out this link.

Emissivity Coefficients of some common Materials

Black paint has a greater emissivity than anodized Al. Sprayed Al does also.

Another factor to consider is where the radiated energy goes. The fins of the heat sink are parallel and closely spaced.
Cheers for the link Steve ;) That's a bit of a shock tbh, i'd honestly have expected a matt black anodized heatsink to radiate better than a painted one!

Not meaning to get in the least bit arguementative but i did notice it's "surface" emissivity that was shown in the table. How well is the heat transfered from the aluminium under the paint & consequently through the paint to the surface? :confused:

I might well be clutching at straws, but it might well add another factor to the situation.

Bests to you, & have a cracking 2010 :) Mark
 
Not meaning to get in the least bit arguementative but i did notice it's "surface" emissivity that was shown in the table. How well is the heat transfered from the aluminium under the paint & consequently through the paint to the surface?

I might well be clutching at straws, but it might well add another factor to the situation.

As is often the case, the answers can be less than absolute. Anodizing emissivity is effected by the thickness of the oxide layer and the coloring compound used. I am only discussing black, but several different pigments can be used, depending on the "shade" of black desired. The same is true for paint or powder coat. With either surface treatment, the real issue is that most of the radiated energy is radiated back to the adjacent parallel fins.

Black anodizing should result in about a 15 - 20% more efficient heatsink than plain aluminium

That is true for flat surfaces or curved surfaces that do not radiate back at themselves. For a typical heat sink, it is more like 1% to 2%.
 
Make sure you account for length and temperature correction factors.

See here
Technical Information - Length and Temperature Correction Considerations

Also see here for effects of anodization
Effects of Anodization on Radiational Heat Transfer

If you note how heat sinks are tested to arrive at those numbers, you will find they do not apply accurately to real world amps. The test is run with one thermal source in the center of the extrusion. If you distribute the same thermal input over several points, the results are different. Most amps are built with more than one source of thermal input to the heat sink.
 
I'd expect that the binder in most paints is not a good thermal conductor at all. The thicker the coating the more so, I would expect. Most of the powdercoat materials that I am familiar with are plastics, like nylon and polyesters, etc. Not good thermal conductors at all. Unless there is some sort of powedercoating material that is known to be "transparent" at infrared, I think I'd stay away from that idea. I dunno, maybe there is such a thing.

The spacing between fins and the depth of the fins plays a very big role in the efficacy of a given extrusion in natural convection service.

The thickness of the rear "plate" plays a large role in the ability of the heat to transfer effectively to the fins at some distance from the heat source(s).

Bottom line is that for high heat amplifiers using natural convection, imho, use the biggest heatsink you can manage to get ur hands on. Too big is better than just a wee bit too small, by a very very wide margin.

Remember to design for the hottest day that you are going to run those beasts! Not for the best case, middle of the winter!!

I'd go to Aavid or Wakefield (do they both still exist?) and use their engineering text for design...
 
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I'd go to Aavid or Wakefield (do they both still exist?) and use their engineering text for design...

They still exist.

Aavid Thermalloy / The world leader in the design, development, and production of thermal management systems.

Wakefield Thermal Solutions

There is a very large difference in the thermal properties of paint. Some paint is designed to insulate, some paint is designed to conduct heat. Filled epoxy powder coat in thickness under 5 mils (5 mils is the maximum thickness) can be as thermally conductive as anodized Al with an organic dye coloring.

Once again, the thickness of either surface treatment will effect the thermal conductivity.
 
Thanks to all for the continued discussion - this has been very helpful! I've been looking around at various heat sinks and it seems that the ones I selected are pretty price competitive. Some time ago, I found some very nice sinks from Seifert, but they were VERY expensive.

The completed chassis will be very close to a total of 0.06 c/w - the same as that spec'd for an Aleph 2, so I'm not worried about not having enough heat sinking available. Yes, I'm sure they will warm the room quite nicely. The basement theater is 13' wide by 24' long with an 8' ceiling and the room is cool all year round.

I'll give all of the links that have been posted a read.

Cheers to a Happy 2010!

Eric
 
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