Thermal conductivity of Aluminum vs. Aluminum anodized

[MEngr3239]

The thermal conductivity of AL5052 and AL6061 is 138 and 167 W/(m*K) respectively. What would be the thermal conductivity for those materials as it black-anodized?

 

[IRstuff]

Across the anodize? or parallel to?

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[MEngr3239]

I have the part in my hand that is black-anodized, but I don't know what surface type of anodizing is applied. It seems to me the surface was treated with fine sandblasting (mild texturing) and then applied the black anodization on the entire surface. So, I don't know if it should be described as "ACROSS" or "PARALLEL". Can you please provide the value of the anodized AL thermal conductivity for both if the delta is not negligible between across and parallel? Thanks. BTW, I am looking for the anodized AL thermal conductivity at 25 degrees C.

 

[swall]

It would help if you would provide a description of the part and the intended service environment.

 

[WKTaylor]

ME3239... please describe the term 'thermal conductivity' in this example/context...

Still air, water, oil, in a vacuum/space environment, part-to part, daylight, night time, 'in a perfect world' or in the real world. etc. context is very important.

Obviously black anodize will affect emissivity... and may affect conductivity... but may be essential for 'real-world' corrosion/erosion/environmental-resistance/durability.

Regards, Wil Taylor
o Trust - But Verify!
o We believe to be true what we prefer to be true. [Unknown]
o For those who believe, no proof is required; for those who cannot believe, no proof is possible. [variation,Stuart Chase]
o Unfortunately, in science what You 'believe' is irrelevant. ["Orion", Homebuiltairplanes.com forum]

 

[3DDave]

The thickness of the anodizing can normally be neglected in comparison to the bulk conductivity.

Your question about "ACROSS" and "PARALLEL" suggests some sort of software or written procedure - what is the source of that question?

 

[IRstuff]

3D, that was because of my question.

Nevertheless, it's pretty clear that the OP can't even describe how or why they even care about the thermal conductivity

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[3DDave]

OK IR. So what do you mean about those directions? I've seen it for direction of airflow across fins, not bulk material properties.

 

[MEngr3239]

Thank you, WKTaylor. Refer to the JPEG files attached. To run a flow simulation with the SolidWorks Electronics Cooling for the simulation case as described in the attached, I need to know the value of the thermal conductivity that I can punch into the item properties of AL5052 anodized. The SolidWorks simulation software provides the AL5052 thermal conductivity as 138W/m*K from its engineering database, but it is for non-anodized surfaces. The unfinished surface of aluminum can be measured at an emissivity of approximately 0.05, while the emissivity of an anodized aluminum surface can be measured at around 0.85. In this condition, what would be the correct # for the thermal conductivity of AL5052 black-anodized power supply enclosure? As shown in the JPEG picture, the power supply sheet metal box is to be subjected to a thermal chamber at 25 degrees C.

 

[3DDave]

If this is going in to another enclosure then most of the emitted heat will be reflected back.

Conductivity will also not matter much as it doesn't appear that it has any place to conduct the heat to.

This will be a convection cooled item - either forced convection if there is a fan, or free convection if there isn't one.

SolidWorks Electronics Cooling appears to perform thermal distribution for circuit boards and the components on them. You need the SolidWorks Flow Simulation module to get the heat transfer out of the enclosure.

 

[MEngr3239]

Hi 3DDave, thank you for the valuable input. As illustrated in the screenshot, the heat resource is to be conducted to the AL5052 anodized enclosure through Thermal Pad, and I need to simulate the outside touch temperature of the enclosure. It is one of the simulation scenarios in which the power supply will be subjected to the inside of a thermal chamber, that is the case you started as "the most of the emitted heat will be reflected back", however, there is another sim-case with no the thermal chamber that will represent a real-world installation in the airline cabin. With the delta emissivity between unfinished and black-anodized AL5052, I need to know how to deal with the thermal conductivity of AL5052 at 25 degrees C in the SolidWorks Flow Simulation. The engineering database in SolidWorks Flow Simulation provides the thermal conductivity of AL5052, but there are no data for AL5052 "anodized". It would be great if you have any info related to my question in handy that you can share in this forum. Thank you!

 

[MEngr3239]

Instead of dealing with the thermal conductivity value for AL5052 anodized, it might be more appropriate to adjust by defining thermal/contact resistance between the components. In this case, do you have some data in handy on the thermal/contact resistance value of the aluminum anodized material that you can share? Thank you in advance.

 

[WKTaylor]

ME3239...

NOTE1.
AL5052 and AL6061... are poor ways to represent these alloys... AL prefix is typically used by scientists or scholars. Engineers see this terminology as 'incomplete/non-descriptive' for these materials.
Here are more typical engineering representations... 'AL' prefix being unnecessary because of the alloy designations...
5052-O, -H32, -H34, -H38 [-H 'strain-hardened conditions]
6061-T4, -T6, -O [HT to -T42 or -T62] [-T* is OEM or user heat treatments for strength]

NOTE2.
Can we assume that the black-dyed anodic finish is intended to be both functional [for abrasion and corrosion] and decorative [attractive/clean appearance]?

Me-thinks... for thin sheet metal... a film sulfuric anodic coating... 0.0004-to-0.0008-inch thick, dyed black and 'sealed'... will likely have very small [negligible] effect on bare aluminum heat sink performance... in the 'real world'. But do be cautious...

6061-T* and 5052-H* are a bit non-standard to anodize and the vendor has to have experience to control the finish. Reason: 6061-T* and 5052-H* alloys/tempers-conditions have amazing 'natural corrosion resistance'... often are simply 'alodined' [conversion coated]... or left bare relying-on their naturally formed oxide film for protection.

Electrical grounding-bonding will be specifically poorer thru any anodic coating... so MUST remove [abrade-off] the anodic coating to attain bare metal contact, at points as needed.

NOTE3.
In the design situation as described, then suggest you consider the following 'light reading' for background 'smarts'...
ARINC 728-* AVIONICS REFRIGERATION COOLING SYSTEM (ARCS)
SAE AIR64 ELECTRICAL AND ELECTRONIC EQUIPMENT COOLING IN COMMERCIAL TRANSPORTS
SAE AIR1277 COOLING OF MILITARY AVIONIC EQUIPMENT
AIR1957 HEAT SINKS FOR AIRBORNE VEHICLES
ARP987 THE CONTROL OF EXCESS HUMIDITY IN AVIONICS COOLING
DESC-DWG-85136 HEAT SINKS, ELECTRICAL-ELECTRONIC COMPONENT, FIN STOCK, ALUMINUM ALLOY
...and any associated corporate documents You may have privy to.



Regards, Wil Taylor
o Trust - But Verify!
o We believe to be true what we prefer to be true. [Unknown]
o For those who believe, no proof is required; for those who cannot believe, no proof is possible. [variation,Stuart Chase]
o Unfortunately, in science what You 'believe' is irrelevant. ["Orion", Homebuiltairplanes.com forum]

 

[3DDave]

Emissivity cannot be considered by changing conductivity.

Just make a simulator with a resistor in a block of aluminum and the thermal pad.

For further help please consult

https://ahtt.mit.edu

The download link

https://ahtt.mit.edu/wp-content/uploads/2020/08/AHTTv510.pdf

 

[MEngr3239]

Hi WKTaylor, Noted well NOTE1. Thanks. Regarding NOTE2, the purpose of anodization to this particular product is for thermal characteristics solely that reduce its surface touch temperature as run the thermal inputs in an ambient and thermal chamber. No functional or decorative but thermal characteristics only. According to your comment on NOTE2, anodized or non-anodized might be negligible with .050" thick sheet metal case. I need to prove the theory by running a simulation study with the correct material properties, but it seems very hard to find that value impacts a reliable simulation result. I will keep looking at internal docs as well as the docs you listed in NOTE3. Thank you so much for your kind support.

 

[MEngr3239]

Hi 3DDave, thank you so much for the input. As suggested, I will add the simulation input conditions with Contact Resistances between the components and will monitor the simulation results accordingly compared with the actual thermal testing results in the lab. Thank you again for sharing the links.