Aluninum heat transfer rate.

[sdold]

Re: Aluninum heat transfer rate.

I've been reading some stuff on painting airplane engines, apparently shops deal with this same subject when customers want painted engines instead of alodined engines.

Boiling down what I've read:

There are two main ways of losing heat: Convection and radiation.

Bare aluminum doesn't radiate (or absorb) heat very well, but painted aluminum does (organic paints). So if your part relies on radiating heat, painting it helps. Color doesn't matter as long as it's non-metallic paint since organic paint all looks black in the IR spectrum.

If your part relies on convection (and if it has fins, it probably does), then paint will insulate somewhat (like everyone here has been saying).

But a lot of engines do have painted fins, so maybe it's OK. I always kind of wondered if painting an engine would make it run a little cooler when at idle (no airflow, like on a bike, when radiation cooling might be more of a factor) and a little wamer when at speed (when convection becomes more important). Anyone ever noticed this?

Bzer: Since objects absorb and radiate heat at the same rate (Kirchoff?), I think painted aluminum would absorb external IR and get hot faster than unpainted aluminum.

Steve

[bzer1]

Re: Aluninum heat transfer rate.

Well I guess I'll chime in as well. I did a search on heat transmission and submission of annodized aluminuim. I don't completely understand the science behind what the engineers said but the jist is that paint and powder will in most conditions act like an insulator as will aonodizing. However in most conditions anodizing is preferred because any bare aluminum that is exposed will begin to corrode. The natural corrosion will have much higher insulation properties than even paint will have depending on the thickness. Also the conditions are very important. In some cases it is better to anodize or powder coat, such as in a high IR environment, because the insulating properties will actually help keep temps even. In a convection or conduction environment it can create problems if you heat tolerances are very tight. Also in the examples given, color could also play a role in both methods of coating. This is a very interesting and confusing subject, because you would naturally think that the rules of heat transfer would be consistant, but according to some of the thermal dynamics engineers the rules change with every variable.

[Banditperformance]

Re: Aluninum heat transfer rate.

Like Hvac said, Powder does reduce the heat transfer. Anno does a little too, but not any measureable amount. I have seen alot of heatsinks for various thengs anno's. Heck, all car audio amplifiers are anno'd. My RC car's Nitro engine heatsinks are anno. I have removed the anno before and have seen no measureable effects on the temp of the engine. The engines run at approx 230-260F

[hvac36]

Re: Aluninum heat transfer rate.

In the field of audio power amplifiers, heat is dissipated by the use of huge aluminum heat sinks.

1. Does powder coating alumninum decreases the heat transfer rate when compared to bare aluminum?

2. What about anodizing. Does this also decrease the heat transfer rate when compared to bare aluminum?

The difference in heat transfer rates may be insignificant to be of any concern but I am curious.

Thanks

Yes the Powder Coat does act like an insulator to what degree depends on how thick of a coat is applied. Does it effect how it cools. Yes. Not sure of the rate.
When I Powder Coat lets say a Complete Engine, the temp on the engine will raise about 10 degrees over normal. So what I do drop the T-Stat by 10 degrees to help off set.
How do I come to the above figure? Well run 2 engines of the same size and make and same cond. The PC 1 will heat faster ( Normally staying about 10 degrees ahead of the uncoated one) then the un-coated engine and will run about 10 degrees higher +/- a few degrees.
Not sure of teh Temp rise or ins factor for the heat sink. Also have no answer for the anodizing.. But I'm sure it does as your covering teh bare metals..

Jim S...

[tylerferrari1]

Re: Aluninum heat transfer rate.

I'm curious about this as well.

If I were to anodize a piece of a aluminum whose purpose was to transfer heat (intercooler), would the aluminum's ability to dissipate it decrease because of the coated surface?

I'd assume it would be, but I'd like to know for sure.

Any one in the know, please let me know!

-Tyler

[mcaswell]

Re: Aluninum heat transfer rate.

Sorry - don't have any information about that.

[levi]

In the field of audio power amplifiers, heat is dissipated by the use of huge aluminum heat sinks.

1. Does powder coating alumninum decreases the heat transfer rate when compared to bare aluminum?

2. What about anodizing. Does this also decrease the heat transfer rate when compared to bare aluminum?

The difference in heat transfer rates may be insignificant to be of any concern but I am curious.

Thanks