[sdold]

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