Cooling things: Difference between revisions
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As in, a little 12V device rated at a few watts, to at most a few dozen watts. | As in, a little 12V device rated at a few watts, to ''at most'' a few dozen watts. | ||
They can eventually pull moisture out of a sealed-enough room. | |||
These are often basically a peltier with two | These are often basically a [[peltier element]] with two heat sinks: | ||
: one large one on the warm side, to drive off heat (just to keep the peltier working), | |||
: one small one to drip condensated water from. | |||
So they will gently heat the air while dehumidifying. | So they will gently heat the air while dehumidifying, but that is an even subtler by-effect | ||
because that will happen at a little less than the watt rating it has. | |||
Revision as of 15:51, 31 January 2024
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.
Sometimes includes adding a fan, to add to the convection.
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.