I've been experimenting with radiative cooling lately and in my mind convection is always an enemy (especially forced convection since the modules are outdoors).
Looking at Newton's law of cooling, it doesn't seem to me that it accounts for surfaces made of different materials losing/gaining heat (can be wrong though, not uncommon especially when working with formulas).
Does it matter (much), that surfaces are made from different materials when we talk about convective heat gains/losses?
I'm only saying this because metal cooled more under radiation than a type of plastic I used, and to me that doesn't make much sense as the convective heat gain should, in my mind, be greater in the metal panel and therefore it shouldn't cool more than the plastic one (both had similar emissivity because of a very thin paint coating).
My experiments tell me that I'm most likely wrong in assuming the convective heat gains/losses will be greater in metals, but I thought it's most likely better to check with those who actually know what they're talking about, it may be some weird fluke in the tests.
Best Answer
I'd expect metals to cool faster through convection because of a related heat property of theirs: conduction. Metals are generally good heat conductors so as heat energy is removed from the surface of the metal by air, internal heat energy in the metal can quickly flow to the surface.
The rate heat flows between two systems is dependent on their temperature difference. When air removes heat via convection, the surface of the object is cooler than the central portion of the object. If heat in the object flows slowly from the center to the surface like in many plastics then the surface stays closer to air temperature and heat transfers to the surrounding air more slowly. If the object is a metal, the heat removed at the surface is easily replaced by heat flowing from the center to the surface and the temperature delta between the surface and the air is greater so the object cools faster.