# Physical mechanics of cooling

## Passive cooling

Passive cooling tends to mean 'what happens with no moving parts'.

...so whatever amount of conduction, radiation, and/or convection would happen anyway.

You're stirring the air better than just convection would, so heat transfer goes a faster than if warm air just sits around - but the difference is rarely much -- convection always does this at least a little when there is temperature difference (if you're in gravity; this is about density differences).

And you could argue that's technically active cooling (because you're adding work, so using energy), but intuitively it feels like it hardly qualifies.

On the technical side

This tends to mean

• conduction - a good conductor spreading heat throughout
if any cooling happens, conduction's spreading brings the whole down
• radiation - thermal radiation means movement of charges in materials (anything above 0 K) is radiated as EM at the surface
(black-body radiation can be seen as a "thermal radiation's real-world math becomes easier if we make some assumptions like that it's not really interacting in other ways")
• convection - fluid flow, in this context often
air,
flow caused by heat changing temperatures and densities
that flow assisting better heat interchange with that fluid, because warmer air moving up tends to draws in colder air from the sides (which technically is an effect that needs gravity)

In practice there's more than one of these happening, but often one that counts for most exchange.